67 PCB/Tach/ and blown fuses - Team Camaro Tech
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post #1 of 4 (permalink) Old Aug 23rd, 14, 12:41 PM Thread Starter
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Tom
 
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Location: Clarence, NY
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67 PCB/Tach/ and blown fuses

I recently pulled the dash apart to fix a variety of little nagging issues. I installed a new headlight switch and replaced all the dash bulbs and the dry rotted A/C vent ducting. Everything worked except the right turn signal indicator. The turn signals worked as do the hazzards, just no right side indicator on the dash.

Then the factory tach stopped working. It was always slow, so I thought it had finally died. I ordered a new tach and got some new bulbs for the TSI. I put the tach in, replaced the bulb and nothing. I traced the problem back to the printed circuit board and saw that the circuit to the tach feed side had a bad spot or missing spot - near the bad TSI circuit. This has to be new because the old tach worked, just slowly. I replaced the PCB and tested the dash cluster in the car with jumpers from the harness to the tach feed, power and the carrier ground wire. The tach worked nicely. I did the same for the turn signals and both worked. Victory!! Not so fast....

I put it all together and the 10 amp fuse in the Back Up/Gauges and Fused Ign slot, that has my ignition wire to the coil in it, keeps blowing when I turn the key on. I have a points eliminator kit in the distributor and years a go I ran a direct line from the coil to the Ign Fused spade to the right of the Back Up/Gauges fuse. Its worked for years. I tried isolating loads by removing the wire to the coil and the unplugging the console gauges and it continues. As soon as the voltage regulator clicks the fuse vaporizes. I am getting 12+ volts across the fuse terminals when the key is on.

I haven't removed the back up lights yet from the circuit yet . I haven't touched this area, my thoughts are that the problem is in the dash. Is there anything on the PCB/tach feeds that I need to look for? Do I need to run the factory resistor wire? Should I run an additional ground from the new aftermarket tach housing to either the carrier ground or its own?

67 Los 3L/4P L48 M20 with C60

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post #2 of 4 (permalink) Old Aug 23rd, 14, 03:19 PM Thread Starter
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Tom
 
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Re: 67 PCB/Tach/ and blown fuses

Since I posted the above, I pulled the tach and speedo out and disconnected the dash harness and the fuse is fine. Using jumpers, I grounded the high beam lamp ground wire and tested the dash lights and they worked fine. With the car running and the ground in place, I hooked a jumper to the red wire in the dash harness - power to the tach and the brown wire - tach signal. With the red wires jumped to the proper place on the PCB, the motor stumbled and started to die as soon as I touched the tach signal to the PCB circuit. So the problem is the tach signal wire.
I researched the issue and there are several causes identified - none of them seem to fit. My thoughts go back to adding another ground or possibly a tach filter. The distributor has a Crane X-7 points eliminator kit in it - very similar to a Pertronix and I have a Pertronix coil. I couldn't find anything recommending a filter for either of these. Ideas??

67 Los 3L/4P L48 M20 with C60

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post #3 of 4 (permalink) Old Aug 23rd, 14, 07:07 PM Thread Starter
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Tom
 
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Re: 67 PCB/Tach/ and blown fuses

To continue this saga and provide help for anyone with a similar problem...I added a ground from the tach housing up to the ground screw in the ground wire by the high beam indicator. This fixed the short and the car runs fine and everything works. I dont' know what caused the problem, but that is the fix!

67 Los 3L/4P L48 M20 with C60

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post #4 of 4 (permalink) Old Aug 23rd, 14, 08:48 PM
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Re: 67 PCB/Tach/ and blown fuses

The 67, 68 cluster used a weird unreliable ground - that paperclip looking thing. It is common failure point. Adding the true real grounding wire from the cluster to the frame solves the issues 100%.


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