I have probably owned this accessory since the early 90s. After making a faint-hearted attempt at using it at the time and failing, it has been stored in the original box in the interim and just came out of retirement. The multiple languages operating manual for its use may be downloaded from http://machineknittingetc.com/brother-ka7100-ka8300-transfer-carriage-user-guide.html. There several video tutorials available on Youtube as well, generally illustrating simple transfers across an entire row in structures such as ribs used for bands and cuffs.
The tool is designed for the standard gauge, transfers only from the ribber up to the main bed. It is best to use yarn that has some stretch. The recommendation in the manual and in youtube videos is to perform the transfers with the pitch set to H. My own ribber is balanced, I found I had problems with transfers in that position, several carriage jams, and to get things to work properly in half-pitch I had to use the racking handle to move the ribber needles slightly more to the left for the transfers. The needles containing stitches to be moved, need to be slightly to the right of the needles with which they will share yarn, that spot may turn out to also be just wide enough to allow for the pattern to be worked without changing the ribber pitch. The yarn used is a 2/18 Merino, knit at tensions 3/5. 
In terms of positioning the carriage, a wire that is akin to that found on Passap strippers is on its underneath. In positioning the carriage on the beds, check visually that it is indeed lying between the gate pegs of both beds prior to attempting to travel with it to the opposite side 
If any carriage jam occurs, it takes cautious wriggling to release the wire and carriage. Upon completion of the transfers, simply lift up to remove it from the beds.
Generally, the ribber tension used needs to be set on 4 at the minimum. The last row just prior to transfers will likely need to be knit at a looser tension than the remaining rib. If the stitches are too small they will not be picked up for the transfer. Folks familiar with lace knitting are aware that just the right amount of weight can make a difference in forming proper transfers. With these fabrics, too little weight may result in loops forming on gate pegs, too much weight, and stitches may remain over closed latches on the ribber needles and not share their yarn for transfers. Again, the transfer carriage operates only from right to left.
Studio instructions for their version of the accessory actually offer some different and more specific recommendations. When knitting full needle rib all the needles or pattern segments the machine generally will be in Half Pitch. Though there are needles in work on both beds, the ribber should be set to full pitch, aka P position, “point to point” prior to transfers, bringing them in close alignment in order to facilitate the process. 
Passap machines accomplish the same by changing the angle of the racking handle to other than the full, up placement in order to achieve the necessary alignment.
The Brother accessory and its parts, has clear imprinted illustrations for use
The change lever has only 2 positions, up and down respectively 
Its position is determined by the number of needles on the ribber one wishes to transfer.
The carriage manual recommends its use after knitting a last ribbed row to the left, but it is possible to use it with both knitting carriages on either side, as long as there is generous space to clear all stitches when the accessory is placed on the bed, moved to the opposite side, and removed. An extension rail may be needed to achieve that amount of clearance.
Operating slowly, one can watch the process of transfers while moving from right to left. Though skeptical, I found the transfers happened easily, with occasional skips. I worked with hand-selection of needles on the ribber to create a pattern, first with hand-selection, then with racking the ribber position to change the relationship of needles on one bed to the other, initially transferred after every 2 rows knit. The knit carriage was set to knit both ways, the ribber to knit in one direction, creating loops on the selected needles, and securing them in the other, allowing for the loops on the ribber needles to be transferred up to the main bed, before working 2 more rows. The “errors” in patterning were operator errors in needle selection as stitches were dropped, and not all the required needles were then returned to work position. Not a technique I would use for all-over fabric, but good practice.
When the transfer occurs properly, the ribber needles will have yarn placed over closed latches, ready to be dropped, the yarn is shared and looped over stitches on the main bed, akin to tuck loops, outlined in the photo with the black oval. The first image is from the manual for the accessory, while in the photo, one improperly transferred stitch is outlined in red. To prevent dropped stitches from happening, any such locations will require a hand transfer to the opposite bed before dropping the remaining ribber bed shared stitches 
For my test I used EON needles on the ribber, planned alternating selection for each new transfer. This could be done by selecting dashes and blank spots on needle tape ie. dash in the above photo, blank spaces below 
It was faster to achieve the effect by changing the ribber relationship to the main bed using racking by one position ie 10, 9, 10, 9, etc. prior to picking up the subsequent set of loops. The errors in the test swatch were from failing to bring all the needles back up to work after dropping their stitches. Using a tool ie. a ribber comb placed over the out-of-work needles prior to dropping stitches made the racking process far less error-prone, will keep the appropriate needles from being accidentally taken out of work. 
My first attempt at creating shapes includes a band at the bottom where the EON transfers as above were made, but every row. Simply bringing needles into work on the opposite bed creates an eyelet. They can be eliminated by sharing stitch “bumps” on the opposite bed, but for the moment they are a design feature. The texture created appears in the areas involved on both sides of the knit 
It is possible to transfer single needles at sides of shapes ie 
or whole rows, but the change lever needs to be set to position accordingly.
Many knitters have one of these tools in their stash, they are sometimes referred to as “jaws”, intended to facilitate transferring between both beds, and patterning was intended for Studio punchcard machines. 
The enclosed punchcards: 
Studio machines select and knit in single pass rows. Brother preselects for the next row of knitting while knitting any one row in pattern as well, so transferring in pattern from the top bed down with such a tool would be problematic to maintain proper pattern needle selection. However, that brings to mind the possibility of having patterning on the top bed to help track patterning on the ribber in some way. This was my start, with the first draft of electronic repeats. 
I stopped when I began to have some tension issues, loops on gate pegs, and a distracted brain.
Transfers of stitch groups, whether by hand or using the accessories are made on rows where no needle preselection occurs on the main bed 
This series is a proof of concept for my approach to developing electronic cues
The original repeats were modified to include 2 blank rows between segments that allow for transfers between beds not hampered by needle preselection on the top bed. The motifs are color reversed, but not the blank rows between them. 
The knit carriage is set to select needles KC I or II, end needle selection does not matter. All needles on the top bed knit every stitch, every row, whether or not those design rows contain black pixels. No cam buttons are pushed in. Blank areas between black ones indicate the number of needles that actually need to pick up loops on the ribber to create shapes, filling in spaces between selected needles until an all-blank row is reached for making transfers. The chart on the far right illustrates a shape where the easiest method becomes one where stitches on the ribber are manually transferred to the top bed in order to reverse the shape and maintain every row preselection. The selected needle corresponding to the black square marked with the top of the red arrows is pushed back, the ribber stitch below is transferred onto it, the needle with the couples stitches is brought to E position, moving across the bed in proper locations prior to knitting the next row. 
In this repeat, the side vertical panels of ribbed stitches are added. The knit stitches on each side of them roll nicely to the purl side, creating what in some fabrics can actually be planned as an edging. 
My takeaway is to test the accessory with some patience, sort out the sweet spot for the ribber needles in relation to main bed ones in terms of handling transfers and yarn thickness, use colors that allow for easy recognition of proper stitch formation, keep good notes, and “go for it”.
A closer look 
with my color changer in this threading sequence throughout
where normally each color in each design row knits twice. Because selection occurs for pairs of rows, the first preselection row is from right to left. To decrease the backing rows, the ribber is set for birdseye. I prefer to have an end needle on each end on the ribber, keeping in mind that the total number of needles in use there needs to be even. The machine provides reminders as to which color should be knitting. My samples are knit using KCI on the top bed. Because the preselection happens twice, it is easy enough to knit in pattern from left to right, 
when the carriages have reached the right side, simply use a ribber comb to push all needles back to B. 
Speeding things up with color separation, beginning with the method that will have each color, each design row knitting twice. The repeat is 10 rows high, so it is expanded X6 to 10 by 60 rows. In the final result, the second row for each color in the separation is in turn erased. The red was added to make all 3 colors visible while working the separation, avoiding confusion with the white ground. The knittable result as usual is in a black and white png 
The img2track settings are for now for 2 color knitting, the prompts for the color changes are lost.
The ribber can also be set to knit every row, resulting in elongation on the knit side, while creating an interesting striper backing
Comparing this version to the birdseye backed one for repeat height 
Comparisons: HoP, pushing back needles to B, and color separation results. In the latter, the design is likely elongated in part due to a change in the distribution of thinner yarns to larger design areas with no tension adjustments 
The Ayab lettering as opposed to numbers move from right to left. The manual states that the color separation order is: white C, grey B, black A with their sequence = C (3), B (2), A(1). If the prompts for changing colors as given are followed it provides a very valuable in tracking them, but if out of habit one knits in the usual 1,2,3 sequence, the color placement occurs in an unexpected order and may result in errors. The on-screen letter prompt corresponding to the anticipated color change sometimes occurs with the knit carriage on the right, sometimes as it approaches the changer, and the size of the font was hard for me to see since the screen was not close enough for easy visibility.
If the png is copied from the post it is likely to appear in RGB mode and it will require conversion to 3 color bitmapped. Its grey color map entry is seen below 
The small file makes for a quick test of proper color selection for each of the three colors used 
Having some idea of stitch counts for each color in the design in the first few rows can help identify proper, planned color placement errors 
My first swatch using the heart of Pluto separation and a greyscale motif 
My tested color change sequence is #1, #2, #3 colors throughout, I disregarded the prompts for color changes at the bottom of the Ayab screen. Some things to ponder: in pieces that require color changes, starting with waste knitting in the same colors can help assess the best tension, whether each color will be picked up properly, and if the colors work well together. Looking at these 3 small tests, it appears that a choice should be made when casting on about using color 1 or 2 for the preselection and cast on rows. If the setting to slip is forgotten for the first move to the left, the color in the feeder will knit every stitch rather than a pattern selection. Always check settings when on the right, making certain lili buttons are set as well. This pattern does not contain 3 colors on every row. In addition to that, when working DBJ with other color separations one is likely used to seeing knit bed needle selections on every row. That is not true here, is a function of the technique, not a patterning error. On rows that have colors missing, when that color is in use, the main bed slips, the ribber works every other needle, first in one direction, then the other, adding to the row count on the purl side of the knit. 
The mess at the bottom was due to the green yarn getting caught on the needle bed and not knitting the necessary stitches on the ribber, so dropped stitches were formed 
The assumption is that if the C, B, A rotation and prompts are to be followed, the middle color 2 can stay in place, and the placement of 1 and 3 can be exchanged.
For a similar effect on Brother machines, begin with all stitches in work on the ribber, with the settings: opposite tuck buttons, the main bed knits to left, ribber knits to right anchoring loops formed on the previous row 
the loops, formed on every needle on both beds with the move to the left 
anchored in place on the ribber needles as the only the ribber knits as it returns to the right 
while the carriage is on the right, drop all stitches on the main bed, 
making certain no loops are stuck on gate pegs on the main bed, 
Knitting was smoother with a change in yarn. An extra needle on each side of the knit on the ribber is brought out to hold manually to ensure their stitches knit with every pass of the ribber carriage. I prefer the all-over pile with its loops formed on the top bed. There were nearly no incidences of loops catching on gate pegs on the main bed. One of the drawbacks, the main bed needles need to be dropped and brought back to the B position manually, bald spots will result where any needles are not returned to proper work position, so they would not pick up loops. 
and this is likely my last try at the single pile in a pattern using every other needle tuck on the ribber with the release of stitches every 4 rows. I actually like the elongated stitches in the ground but found the stitches planned for loops simply did not release easily or at all, 
Using the method described in other posts, this was the screengrab imported into Gimp. The grey line is a reference point. Cropping the image to content will allow the last blank row to be preserved by having the grey one there. After the crop, it can be bucket filled with white, or when the image is, in turn, bitmapped to B/W, you may find it disappears. Image scale is then used to reduce the repeat for knitting. 
plaiting with yarns swapped in feeders for reversible striped effect 
A mock plaiting effect may also be obtained without a special feeder by locking the pattern on any all blank row, the standard yarn feeder with A and B yarn placement, and the fair isle setting. Results are not as consistent in color distribution.
Canceling end needle selection applies in any situation is used in a tuck or slip stitch settings if there are needles out of work on the main bed for any reason to maintain proper patterning in needles in work. Electronic knitters have the KCII option in the change knob.
More random, ancient swatches: stocking stitch using equal weight yarns in a single bed tuck stitch 
double bed every needle rib tuck stitch using the same pattern repeat 
When working on large pieces especially, the yarn in the front feeder especially may have a tendency to slip out. This is one option for helping to prevent that when the ribber is in use 
The suitable dbj separation is the one where each color in each row knits for 2 rows, whether performed by hand, using the 3 colors per row separation in img2track or the default separation in Passap. The Ayab HOP separation is awesome, works for any 3 color design with as little elongation as possible, but is not suited for this purpose. How-tos for DIY separations and their automated versions by programs for knitting more than 2 colors per row have been discussed in other posts.
A similar process on the Passap allows for playing easily with both racked colors because of the possible arrow and pusher settings on the back bed, but on Brother, this would require hand selection on the ribber on every row or a specific color separation for needle selection on the top bed
Seeking automation, keeping things simple, here is a basic zigzag pattern in a repeat also executable on punchcard machines. The ribber is now set to knit throughout (N/N), the main bed to slip in both directions. End needle selection must be canceled when using the slip setting selectively or when working patterning with needles completely out of work 
The process using 3 colors: the patterning color will be knit on needles preselected on the top bed. As shaping is about to begin, in this pattern, one needle preselected out indicates the location for an “increase”, one preselected back to B position a decrease 
To perform the decrease, using a double eye tool to transfer the B position stitch down onto the ribber needle adjacent to the first needle in D position on the top bed
The repeat and the knit shown on both sides: 
Comparing the 2 color and 3 color versions: aside from the obvious increase in length, note that the slipped segments in red on the 3 color swatch are now composed of longer stitches since they are held for 2 additional rows, and the overall fabric is more puckered than the 2 color version. The curling at the sides is the nature of edge stitches, especially if the yarn used is wool. At times that may be used intentionally, as a decorative edge.
Using the same color separation as for the simple zig-zag shape, the design is expanded to include knit bed rows that will be skipped completely, resulting in the ribber alone knitting in the second color for those rows. It is now twice as long as the original, 24X64
The planned proof of concept added a 4 stitch border on the right for a 28 stitch swatch centered with 14 stitches either side of 0. Tiling the repeat X2 again in height made it easier for me to plan how to manage transfers to expose the varying stripes in the ground. Visual comparison to the movement in the inspiration knit: 
As the number of needles in work on either of the 2 beds is increased, it is likely tension or yarn changes may be required. The first preselection row is from the right, toward the color changer. The stitches on the non selected needles are transferred to the bottom bed 
with the color change, only preselected needles will knit on both the top and bottom beds moving to the right 
and will do so again on the return to the left while preselecting an all blank row 
on the next pass to the right only the ribber knits in the ground color; 
Back to the drawing board in order to reduce the number of hand manipulations involved, with a shift in the center transition, the repeat in my spreadsheet is now 24 stitches wide, plus an additional 4 stitch border, and gets marked up with colors. I prefer to program the width of my knitting as opposed to a single repeat for all over patterning 
The choice can be made based upon the preference of moving stitch groups to the right or to the left with the horizontal direction of the repeat adjusted for your KM model or software used. 
I planned the transfers in this swatch toward the color changer after picking up the proper color, white, and before knitting the next row using it. The 930 png: 
The preselection row is from right to the left, toward the color changer. End needle selection is canceled. All stitches not selected on the main bed are moved down onto ribber needles beneath them. Needle selection takes care of the increasing angle in the surface yarn (white), as less of the striped ground becomes exposed. At this point, row 34 on the 930 counter, the single elongated slipped stitch is moved down onto the ribber. 
When the top of the repeat is reached, row 68, the only needles selected will be those of the 4 stitch vertical columns and the design repeat will return to its start
My proof of concept swatch is 3.75 inches wide 
The inspiration sweater was knit using a wider repeat and significantly thicker yarn, reflected here in the small number of repeats composing the sweater body front 
The off white yarn used here was the same thickness but not fiber content as in the previous swatch, 2/18 wool-silk vs Australian wool in the former. It is not as smoothly spun. The result shows an interesting similarity in length, though there are 16 additional rows in the pattern repeat. This time I programmed my repeat for stitch transfers on the knit bed to move away from the color changer. 
Eliminating the border on one side, a double repeat (30 stitches) measure 4 inches in width. To put the difference in scale to the sweater in perspective, an oversize garment with 40 inches in chest diameter would require 20 inches in width for the front piece. Ten single repeats, as opposed to the inspiration’s sweater 4, bring the total required the number of stitches to 150. With the added border of 5 stitches for matching side edges, the fabric is in the realm of possibility for producing a garment on the home knitting machine. My tension was set at 3/3 for all the swatches, with some teasing required on occasion to encourage stitches on the main bed to knit off properly. Ribber height adjustment can also have an effect on those numbers. I tend to do all my knitting with the slide lever in the center position. The double 30X84 repeat with no added border
There have previous posts on automated lace edging on Brother machines, ie 
Here the same pattern was executed on the same number of stitches with the white wool used above, but the elastic was plied with a 2/24 acrylic yarn and knit as DBJ with the blue, stretchy combination creating the solid color backing. 
The same pattern repeat knit with striper backing is far less interesting 
to this, 
The appearance of the fabric when stretched and weighted, still between the beds 
and off 
Going the far more traditional route of traditional dbj with use of the color changer, striper backing with the ribber set to N/N yields a wider, flatter fabric with an interesting purl side 
The birdseye version had more of a bent on
I found the fabric attractive on the purl side, but I was having issues with dropped stitches I could not explain that would need sorting out if producing larger swatches. 
Adding a third ply of elastic was disastrous at any tension. Better results occurred simply by increasing the ribber tension by 2 whole numbers, the knit tension by 1, and reverting to the previous yarn usage. There is a single dropped stitch in the elastic, and the result has much more of a 3D effect. 
