Tach adapter with Crane HI6S

[whyfeel]

I have a Crane HI6S system installed on my car with the optical trigger conversion in the distributor. It's an '82 n/a s130 with stock EFI. Here is what the wiring looks like.

 

 

It works. I need to get the tachometer working correctly. I couldn't find Crane's 6000-8920 but I got MSD 8920 Tach adapter. I hope they are the same basic piece of equipment or I am wasting my time. I have been trying to get it hooked up with everything. In my above poorly drawn wiring diagram the Tach Adapter isn't going anywhere. I was trying to hook it up however the Crane wiring diagrams show different color wires than the MSD wiring diagrams. So I started messing with it. If it is a sensitive piece of equipment I hope I didn't ruin it.

 

Tach adapter, four wires, black, red, white, and purple. Black is obviously ground. Red I hooked up to coil positive wires. I assume that this is just switched 12v positive for entire system. Then I hooked the white Tach adapter wire up to the coil negative/white trigger wire for the optical and the HI6S. I left out the purple wire. The engine ran and no change to tach. I assume that is because the HI6S, optical trigger and the adapter were all hooked up to coil negative and this circumvented any adapter circuit.

 

Secondly, I ran red to coil positive and black to ground. Then I hooked ONLY the adapter to the Coil negative. Car wouldn't start, assume that is because in this setup the optical trigger went to the HI6S white wire and whatever the white adapter wire fed into Coil - didn't trigger fuel, my HI6S trigger led was blinking so it was working.

 

Thirdly, I ran red to coil + and black to ground. Then I hooked the white adapter wire to the HI6S white wire and optical trigger (still leaving it out of the coil -). Then I put the purple wire to the coil - thinking it might be the signal out after "attenuating" the tach signal or whatever it does. In this mode the car started but ran extremely rough, wouldn't do more than idle sporadically, dying as soon as throttle was applied. This is most likely not the way to set it up.

 

The last try, I put red to coil + and black to ground. Then I put the adapter in between the HI6S and the optical trigger on the white wire coming out of the HI6S. The the white wire on the Hi6S went to the white wire on the adapter, then the purple adapter wire went to the coil - and optical trigger. This filtered out my optical trigger sensor, so my HI6S status led didn't blink and it didn't start.

 

So, I am not doing it correctly. I assume either a) the MSD 8920 box doesn't jive with the Crane Hi6S because it is designed for a different ignition type or I need to go behind the dash and find the wires coming out of the tach, then run the adapter wires red to coil +, black to ground, white tapped into the intact optical trigger/coil -/hi6s white wire to pick up the signal. Then figure out which tach wire is for signal, cut it and send the purple adapter wire directly to the tach.

 

Any help would be greatly appreciated.