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post #1 of (permalink) Old 09-22-2005, 11:01 PM Thread Starter
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CJ7 factory tach wiring

My friend has an 86 CJ7 that came with an auto. It now has a NV4500/D300 and is in desperate need of a tachometer (258 doesn't like going to 6k like my SBC, that's for sure). He found a factory I6 tach but the wires are cut off. Two go to the bulb and two go to the tach. The tach part has a red wire and a red wire with a white tracer (someone cut the socket off).

I tried making it work like all aftermarket and factory Chevy tachs and it just kills the motor. I think we managed to cook the points (PO went to points and condensor instead of just disabling the crackpot AMC emissions wreck of Ford's trusty Duraspark). So, we converted it to HEI using a bunch of Chevy and Chrysler parts. It still kills the motor.

Anyone got any ideas or know where these wires are supposed to go to?
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post #2 of (permalink) Old 09-22-2005, 11:06 PM
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Re: CJ7 factory tach wiring

There are two wires in the loom....real heavy gauge....matching connectors....the tach goes between these wires....same connectors...

If you take the tach out, you connect the two wires in the loom together...put the tach in, and the two wires go to the tach.

I have a tach that I no longer need (doing an SBC swap)....$10 + shipping and it's yours....You can also buy a new one from Krage....I think it is about $50 or so.
post #3 of (permalink) Old 09-23-2005, 03:47 AM
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Re: CJ7 factory tach wiring

It goes right here in the harness:

Or in a little more detail:

What you do is to seperate the plug and insert the tach wires. THis is because the CJ tach is a SERIES tach meaning it goes in series with the device.

Batt---Ign Switch----Tach---Coil(+)^^^^^Coil(-)----Points

Unlike aftermarket tachs.

Batt----Ign Switch-----Coil(+)^^^^Coil(-)----Pints

And yes, since it acts as a wire, it will kill the engine right away it you try to hook it up the conventional way.

In your case it will be:

Batt-------Ign Switch-----Tach------GM HEI (+12V)
Or the one side of the tach will go from your ignition switch and the otherside will go to whatever terminal supplies power to the distributor. DON'T hook it to the "Tach" terminal.
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post #4 of (permalink) Old 09-23-2005, 06:32 AM Thread Starter
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Re: CJ7 factory tach wiring

WOOHOO. Thanks. I was wondering if it needed to be in series or not. We found those wires under the dash a couple weeks ago but I couldn't figure out what was going on so I was doing all the stuff out at the distributor.

I was wondering if it was some kind of inductive tach that got its signal from the power wire. It makes a lot more sense now. Thanks very much.
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