RPM Gauge Wiring

[ThisGuyUKnow]

I still have not found a good schematic for my 85 Laredo . I am chasing down a handful of gauge issues that I am have a fairly good handle on. What I don't have a handle on is the RPM Gauge.

here is the deal, the RPM gauge worked when I first got the jeep. At the time it had an MSD coil and MSD distributor with a holley 4bb carb. Since I have swapped out the system to a GM TPI setup (very similar concept to TBI) and now no RPM gauge.

I know that the CJ RPM gauge is a little unusual in that it reads from the pos side of the coil instead of the negative. However that is where I am confused, essentially the coil for my new setup is electronically similar as before. The wiring harness still hooks to it through the same exact wire, What IS different is that I removed the ignition control module off of the fenderwell. The GM TPI has an ignition module which I installed inside the HEI distributor with the coil.

I can only speculate without a schematic, but does the ignition control module have a role in proper operation of the OEM RPM gauge? If so I may be able to get it to work with some wiring but I cant find anything on google.

 

[gert]

not 100% sure on the actually operation, but I want to say that it uses the voltage fluctuation from the positive side of the coil to trigger the tach I found a link for you. If I remember right you still have HEI? If you do it has a tach source plug in the cap The Jeep CJ Webring

 

[ThisGuyUKnow]

not 100% sure on the actually operation, but I want to say that it uses the voltage fluctuation from the positive side of the coil to trigger the tach I found a link for you. If I remember right you still have HEI? If you do it has a tach source plug in the cap The Jeep CJ Webring

Gert that is also my understanding as to how it works. That is why I really am not sure why it doesnt work now since it worked prior. When I installed the HEI I connected the exact same Pos wire from the original coil to the pos of the HEI coil.

 

[gert]

Gert that is also my understanding as to how it works. That is why I really am not sure why it doesnt work now since it worked prior. When I installed the HEI I connected the exact same Pos wire from the original coil to the pos of the HEI coil.

To the hot on the HEI or to the tach signal on the HEI ? I think they are the same but cant remember right now, nothing from the MSD still in the wiring harness?

 

[gncolli]

I tachometer is pulsing. After much searching I am thinking it might be related to my Ignition Radio Capacitor. Per readings this could be my root cause. I have ordered a replacement since the one on the side of my coil looks really bad. I will report back when I get the part.