This is a 1983 era tach.
The red wires(one has a red stripe) are a loop that goes to the coil and (I believe) through the ingition module.
This is an old question on this board and an adequite answer has never been posted. The wireing diagrams are vague as to where the red wire goes after it leaves the coil and how the ingniton module handles the pulses made by the coil.
The last time this question was posed, Larry Van Every gave it a crack.
Here is his take on it if this will help though this particular application may not corrispond to the two-red-wire syle tach as there are several other wiring schemes both prior and after this one.
Needless to say, you chose a very difficult style to try to convert to your system.
On the bright side, There are plenty of CJ folks that would love to have this two wire unit, probably bad enough that they would pay you the price of a new, universally comptatble AutoMeter.
Just post it in the For Sale section of Off-Road classifieds an you will see what I mean.
Posted by LEVE
Posted on Wed Nov 3 22:53:55 1999
Well, if no one else will tackle this problem I will give it a try. I just installed a GM HEI two weeks ago with my Howell EFI System.... and it seems to be working fine. So, let's look at the TAC…
A TAC is driven by current. The current is supplied by the pulse from the ignition module. The ignition module differs in VOLTAGE levels from manufacture to manufacture, however the job the module does is the same. In fact, in a pinch, if you know all the connections of each of the OME modules, GM, FOMOCO, and DODGE, you could make up a set of swap connectors and connect a GM ignition module into a FOMOCO system and vice-versa. Things will work just fine.
Now the rub….if the pulse produced by the module is insufficient in width, duration or amplitude, the TAC may not work…
If you want to make sure the OEM TAC works with the GM HEI distributor, run the two modules in parallel. Here's what I mean….
Leave the OEM FOMOCO ignition module in place, connected to the harness, but with the FOMOCO Coil out of the circuit..
Now run a spade lug/wire connector from the GM HEI TAC connector down to the COIL TAC pigtail and connect the two together. Start the Jeep, the OEM TAC work.
Now turn off the Jeep and then unplug the OEM FOMOCO ignition module…
I'd bet the tack will still work… however unless you did the Nutter Bypass, the OEM Computer will be brain dead!
Let me know how it works.