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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: 84GMCSierra on April 17, 2021, 03:29:11 pm
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I'm trying to install an aftermarket tach in my 84, but can't get anything out of it. I have it grounded to the dash, the red wire is hooked to the only terminal marked "IGN", and the green wire is plugged into the terminal on the cap marked "TACH", but no luck. I was told on another site to tap into the white wire coming out of the tach port on the cap, but that only goes to the plug for my ac compressor. There are 3 other wires coming out behind the white wire: Brown, Black, and Pink/Red. Do I need to tap into one of those to make the tach work? (I can't post a photo of the wires as the photos are to large.)
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Info about my truck
350/TH400, 2wd. All stock
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The TACH terminal on the distributor cap is the correct location to acquire a tach signal. Do not connect to the black, brown, and pink wires, behind.
Use an incandescent test light to verify ignition power at the IGN tap to which you connected. It could have a blown fuse. Then use the test light to verify power and ground at the appropriate terminals on the tach head. Finally, use the test light to verify that there is a tach signal reaching the tach head with the engine running. The test light brightness should increase with increasing engine RPM.
What do you mean that the white tach wire connects to the AC compressor?
Downsize the images to post them or use a third-party hosting service.
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Ok. Update time. Tach is working...kind of. When I start driving, it goes to 3500 rpm. When I start slowing down coming to an intersection, it drops to zero. I'm going to double check my ground as it's on the lower front part of the dash. Any ideas besides possibly a ground issue that I'm not thinking of?
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I had a similar issue. Grounding it to the dash metal was the problem. I ran the wire down to the grounding post at the emergency brake pedal and haven't had a problem since.