Can't get my stock to work

[gopedal]

I bought an 85 CJ6 cyl. Totally redid it and put a/c in it. When I began to actually run it my tach didn't work. I had to pull the tilt steering wheel back out and I decided to get the tach working. I did a nutter bypass on the jeep early on. I know there are two red wires, one with a white tracer off the ignition switch and the other goes somewhere in the harnass, I think back to the positive side of the coil, that connect to the tach wires; I had them connected. When I put a volt meter on the wires the one with the white tracer shows me battery voltage as it should. The other does nothing. I ran a wire from the positive side of the coil to the plain red wire on the tach and I connected the red wire with a white trace from the tach to the red wire with the white trace from the ignition switch. I saw a faint spark between the wire ends and tach pointer jumped and went back to 0. I've studied all the wiring diagrams and read on several forums trying everything. Aside from the tach in the jeep I have two other OEM tachs laying on the floor that I try everything with as well, they all have done the same thing every time. When I connect the red trace wire from the ignition switch to the other red wire through a voltmeter, (neither wire comes from the tach) I get battery voltage. The only other thing I might try before going to an aftermarket tach is to connect to the Black wire from the ignition module and be certain it has a good ground. Other than that, I've about exhausted everything I know to try. Any suggestions?

 

[Cheepjeep85]

You may have fried your tach. the signal wire from the tach should connect to the negative - side of the coil. And the wire powering the tach should be switched 12 volts. And of course ground to a ground. you should be able find the tach signal wire with a factory wiring diagram. Now if you aren't sure about the factory wire harness you might be better off pulling a new wire from tach to coil.

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[gopedal]

CheepJeep85 - Take a look at this URL and tell me what you think. Thanks.

Jeep CJ Tach Wiring

 

[CJ]

Have you checked continuity from the tach connection to the coil connection? Do this WHITHOUT having the tach wire or the coil wire connected. Also check the tach by bypassing the wireing on the harness completely and run a wire directly to the coil.

Is everything else working correctly on the dash? I believe the tach connection goes through several plugs before it goes to the coil.

 

[Cheepjeep85]

Do what cj said first, but I'll add this, my tach is connected to the negative side of the coil. The positive side is nothing more than a switched 12 volts, the coil gets its signal to fire from the negative side of it. That said I'm running the tfi with gm hei ignition module, and a aftermarket crown factory style tach. Somebody correct me if I'm wrong here, it has been a while since I wired mine.

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[gopedal]

CheepJeep85, I'm sure you're correct about wiring using an aftermarket tach. The only tach I've ever seen that runs to the positive side of the coil is the one in amc CJ. Somehow the tach senses the pulses of the positive flow as the current flows to the positive side of the coil through the tach. I'm not sure if that is better or worse than what I always considered normal tach wiring like you described but it is the way AMC tachs are wired. Yes CJ I tried direct wiring and the tach wouldn't work. Not surprising, neither 6 cylinder tach I have works. When I plugged the ignition switch into the sytem and wired the tachs as per normal wiring, neither worked but when I unplugged either side of the tach the jeep would shut off. I plugged in an 8 cylinder tach I have and it worked. I'm in the process of removing a 6 cylinder tach I have in a jeep with a AMC 304 in order to have a 6 cylinder tach for the 85. I'll put the 8 in the AMC 304 and finally both will be correct. With AC in both jeeps I have to pull the steering columns to get at the tach. Still not an easy task but I'm halfway there. Thanks for the help.