Author Topic: tach problems  (Read 1430 times)

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Offline toqwik

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tach problems
« on: December 12, 2007, 05:35:18 PM »
Anyone have any idea why my tach works in the crank position, but once the key is let go to the run position, it goes dead....

Offline brian c

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Re: tach problems
« Reply #1 on: December 12, 2007, 06:31:13 PM »
Did you take the cluster out at any time? If so you might be missing a ground. Try grounding the case of the gauge pod to see if that fixes it - did on mine. It's worth a shot.

1978 Y88, '70 455 HO block bored 0.060, TH350, 3.42:1 gears...Oct '08 Fbodywarehouse Calendar - Woot!
1980 Firebird - no engine/tranny... to be pacecar clone

Offline toqwik

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Re: tach problems
« Reply #2 on: December 12, 2007, 09:58:00 PM »
From the looks of it, it's been out a few times.  What holds it in anyways?  All my bezels are missing, and someone mounted guages in the a/c holes ::) ::)

Offline brian c

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Re: tach problems
« Reply #3 on: December 13, 2007, 07:17:05 AM »
A few screws hold the gauge pod to the dash structure. Since the dash is mostly plastic you're not getting a ground from that. Just for testing purposes you could take a test lead while the car is running, ground one end to the metal dash and touch the other end to the gauge pod. If the tach suddenly starts working then you know its a ground issue.

If that's the case I'd pull the gauge pod and check the wiring harness. There's probably a solid black wire with a ring terminal on it flapping in the breeze. Try connecting that to a good ground, putting the pod back in and retesting. It may solve the problem.

Then again as a last resort if you look at the back of the gauge pod you should see a couple of posts marked GROUND. You could make up your own ground wire with ring terminals and connect it there and a good ground under the dash - again a good metal ground.

Since you mentioned aftermarket gauges, you might also want to inspect your wiring harness to see if its been hacked into.

One final thought...the tach harness is a two pin connector (pink and white wires). If that's not connected to the back of the tach you're not going to get a signal.

Good luck and let us know how you make out.

1978 Y88, '70 455 HO block bored 0.060, TH350, 3.42:1 gears...Oct '08 Fbodywarehouse Calendar - Woot!
1980 Firebird - no engine/tranny... to be pacecar clone

Offline toqwik

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Re: tach problems
« Reply #4 on: December 13, 2007, 11:43:15 PM »
It just doesn't make sense that it works while the motor is cranking, and not running.  Definately gonna pull the dash and check the ground.  What exactly holds the dash in place?  I lnow mine is loose, but what holds it in?  Also, what holds the plastic bezels in that go around all the guages? my bezels are all missing......

Offline ta78w72

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Re: tach problems
« Reply #5 on: December 14, 2007, 10:01:50 AM »
Little fasteners hold the plastic bezel in place.  You don't need to pull the dash to fix the tach.  First check the pink wire that goes to the tach.  That wire can sometimes have a fuse holder in it.  Check that fuse.  With your volt meter and with the car running, check the pink wire for 12 volt.  There are only two wires that go to the tach.  The pink one with 12 volts, and the brown one that picks up the pulse from the distributor.  The tach gets its ground from the cluster housing, so you could run a temporary ground from the nut above the connector terminals (that's where the tach is actually grounded) to somewhere on the body of the car.  However, first check that fuse.  I have a document on how to remove the dash, if you want it send me your email address.  It will tell you where the dash is connected.  I also have a document on how to pull that cluster if you can't figure it out. 

On the ground, if your cluster lights work, you're grounded.  However, it's always possible that the ground circuit could have broken before it hit that ground screw and nut for the tach.