Sorry for going silent for so long. I've been sick most of the week and haven't done anything, including getting online. I read your posts and saw you're on a good track for getting your cluster wired. When I started reading and first saw your idea you did have the trans harness I was going to point you but saw you got it all figured out.
One note, it should go without mentioning that there are only 2 wires to the VSS. One wire goes to ground and the other to the harness for VSS signal output. Make sure you're tapping into the output leg and not the ground leg. I'd be happy to provide the wiring colors from the factory harness but I only have the '91 and '92 Ford manuals and wouldn't want to lead you astray. Mike (Mustang5L5) may be able to supply you with that.
I noticed you were concerned because you weren't running the EEC but instead had a microsquirt. Have no fear as it' doesn't matter. When the trans harness comes into the car it gets connected behind the left kickpanel. The VSS signal output is divided out at this interior connector. One run goes to the Cruise Control Amplifier and the other goes over to the EEC plug. Neither component is required to be hooked up. You're just using the VSS
output signal. There is no power running from either component to the VSS is simply provides a reference
input signal to those components. You can almost think of the VSS as a signal generator. The signal is not a power input or output but a reference to ground. It wouldn't be though of as voltage but frequency. Without over complicating it any further than I just did, as long as the VSS is installed in the trans and the factory plug is connected to it, you can simply tap your DD controller wire into the factory harness for the needed signal. It's a digital system so you can't necessarily apply "voltage thinking" to it.
Based on earlier comments I imagine you already have much of your wiring done so this may be a little too late. I was an aircraft electrician for over 15 years and am TOTALLY OCD when it comes to wiring and wiring mods. "Pretty" wiring jobs not only look nice, they are more dependable and easier to work on. With that said I really, really wanted to use the same colored wires for wiring to my controller as the factory wires they were being tapped off of. Most folks are happy just going down to the auto parts store and picking up the biggest assortment of colors they can find and they're (I think a large number also don't care and at all and will just wire everything with the same colored wire). Labels are an option but as I said, I'm OCD! After some searching online I found a company that sells automotive grade wiring in different gauges and multiple colors WITH multiple color tracers on them. They sell in single spools of different lengths or "kits with multiple color option in multiple length choices and color choices (e.g. 10ft lengths with 4 color choices). I was able to match up all of the applicable wire/tracer colors that are used in the factory harness and ordered their 10 color kit in 10ft lengths. They specify in the listing what color combinations come in the kits. As soon as you place your order though all you do is immediately shoot them an email with YOUR color choices and that's what they put in the kit instead. it cost me $27.95 (free shipping) and they were really fast and I got exactly what I asked for. The company is :
4rcustomswire. The single thing is that their tracers are marked spiraling down the length of the wires instead of straight (like factory wire). They state they prefer this way in order to more easily locate the tracer on the wire...and that is a valid point.
I know the DD cluster isn't cheap but man! I was blown away by the quality and craftsmanship...in addition to being 100% USA made. If you REALLY want to see how much you really got for your money, go to their factory tour on video Youtube. I bought mine from LMR and couldn't wait to tear that box open when it arrived. Keep us up to date on your progress with the install. Seems not too many people here have pulled the trigger on one. I'm happy I did!!