[ET48]

I have the original tachometer in my jeep and it reads rpm but about 1,000rpms too high. When I start the jeep the tach stays at zero until I tap on the glass. The tach also moves very erratic. Up and down and not steady with the engine rpms.

I have checked the ground and the wires to the tach and they look fine. There are four wires that go to the back.

Black-ground. Orange-power for backlight. Red-Ignition? Red with white stripe-Coil or computer?

When the key is on I have full power at both red wires, and the same when started. If I unplug the red wires or just one of them the engine shuts off. Can someone please give me some suggestions?

[SirGCal]

Engine dies from unplugging the TAC? That's not right... But I'd have to see it to know where to look. Sounds like something is going THROUGH the tach which shouldn't be happening. It should just be getting a pulse signal through the coil or wherever.

[ET48]

Someone else said the factory tachs were wired in series with the ignition system. The tach measures the volts going through the ignition and not from the coil. All cj jeeps were like this I guess from the factory. All newer tachs and aftermarket tachs plug into the coil. I ordered a new tach so I will see how that goes. Thanks.