Where to tap in for external Tach? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 02-24-2008, 11:47 AM   #1
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Default Where to tap in for external Tach?

Ok, so I am wanting to verify if the tach in my Bonne is off to determine if I actually ahve a high idle problem, so I have a Sunpro Super tach II laying here that I want to hook up to determine this. Where is the best place to hook it up? I know the white wire on the ICM harness is the tach wire, as I used the same one to tap into on my '94 Century and '96 Ciera. But, is there a easier way than cutting into the wire? TIA!
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Old 02-24-2008, 11:52 AM   #2
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Not an easier way that I know of. You could use a vampire tap (or clamshell splice), under the fusebox cover in the engine compartment. That would be the most protected place that I can think of. Or, backprobe the white wire at the ICM connector with a paperclip.
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Old 02-24-2008, 11:57 AM   #3
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Hmmm....think you can show me the area to tap in under the fusebox cover? It would be appreciated.
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Old 02-24-2008, 12:04 PM   #4
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Not while I am at work...but it should be easy enough to trace if you have a meter that shows you continuity. You will want to place one of those probes where the ICM harness connects to the main harness, and the other will have to be the prober for the white wire going into the firewall harness.
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Old 02-24-2008, 12:16 PM   #5
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Use your scantool to see what your RPM'* really are.
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Old 02-24-2008, 12:42 PM   #6
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I don't get a tach reading on the scantool. :(
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Old 02-24-2008, 03:35 PM   #7
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If you have the CP9110, you do. Look again.
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Old 02-24-2008, 04:05 PM   #8
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Default Re: Where to tap in for external Tach?

Quote:
Originally Posted by Bonneville92V688
I know the white wire on the ICM harness is the tach wire, as I used the same one to tap into on my '94 Century and '96 Ciera. But, is there a easier way than cutting into the wire? TIA!
It'* the same wire. If you want to hook the tach up somewhere more or less permanetly, then trace that wire back as far as it goes in the harness and tap in there. I don't use "vampire" taps. My taste is to take the pin out of the existing connector shell and solder another wire on the same connector (so two wires come out the shell where there used to be just one.) That way I never need worry about the tap cutting the existing lead. When I did the tach on the '90 Bonnie, I didn't even have to do that...the tach wire dead-ended where the ignition wiring met up with the rest of the harness..I had to add the missing pin.

BTW, does your tach have setings for a V6? The tach signal is only going to be 3 pulses per revolution, not the 4 pulses of a V8 (which most aftermarket tachs come configured for.)

If you just want a place to test the tach signal comming out of the ignition, stick a straight pin into shell from the back (parrallel to the wire)...that way you can touch the contacts inside the shell without disturbing the wires.
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