If you are using the factory tach, it's "in-series" with the ignition power.
So, the wiring should go ignition switch ---->tach---->HEI.
Most guys splice into the large 10 ga red ignition wire, near the firewall connector, to power the HEI. That way, you don't have to change the factory tach wiring,
If you are using the factory tach, it's "in-series" with the ignition power.
So, the wiring should go ignition switch ---->tach---->HEI.
Most guys splice into the large 10 ga red ignition wire, near the firewall connector, to power the HEI. That way, you don't have to change factory the tach wiring,
I just went through this last week on my CJ5!
As soon as I put the HEI distributor in, I immediately connected my tach to the "TACH" terminals. Who needs instructions!??
Not only did the tach not work, it wouldn't run!!
Eventually, I realized it was the tach preventing the HEI from working.
I next temporarily supplied the HEI with power directly from my battery...worked great!
Then, I ran to this forum to read about the factory tach wiring (I added an old OEM tach a while ago)
Since my OEM tach already was tied into keyed power, I wired it in series with the HEI.
Then it would only start when I released the ignition key from "start" to the run position.
Whatever wire I had supplying the tach, didn't supply 12V while in "start".
So, being the brilliant engineer that I am, I simply added a jumper from my starter solenoid to the HEI, so I would have 12V while starting.
Well, needless to say (or maybe not!), I ended up backfeeding the solenoid, so it wouldn't disengage the starter!!
Phew!!
I finally found the correct 12V power to run through the tach, but it took me an hour or so of dicking around.
So it's working great now, and thanks to you guys, I have it wired ignition switch------ tach------ HEI.
Its really not is that difficult. The Painless harness will have a main power wire from the ignition switch to the ignition module/ HEI. The factory tach needs to be wired "in series" with that wire.
Ignore any wires that reference "tach" on the harness or HEI. Those are intended for a different style of tach.
Matt
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