Hey CO Folks,

I am at the tail end of a long restoration of a 69 442 and the last issue I am trying to overcome is a short within the gauge circuitry. The car was originally equipped with the idiot lights and no tach and I chose to add the Rally Pac for the restoration. I also purchased all new factory correct harnesses for the Rally Pac setup. I have made sure to check the pin configuration on the gauge cluster and that is correct. However, as soon as I replace the 10A fuse on the fuse block and turn the key it shorts immediately. Strange thing is the following works between the gauge cluster, speedo and tach/clock: Clock, E-brake light and speedometer. The three gauges read the following;

Fuel - Almost F (actually only has about 2 gals)
Temp - 1/4 mark
Oil Pressure - 1/4 mark

None of the instrument lights are working at this point either. Tach does not work as well.

I went through the wiring diagram in the CSM (for Rally Pac) and I cannot find anything that stand out that would be an issue. If anyone has some recommendations as to how to troubleshoot the issue I would really appreciate the help.

Sean

 

Are you sure that the metal ground straps are in place on the backside of the plastic dash?

 

Joe,

Yes, I double checked all ground straps and wiring and they appear to be in the correct spots. Would a lack of ground cause the fuse to short? Electrical is not my strength.

Thanks
Sean

 

Sorry, I missed the part about a short that blows the fuse. Sounds like a pinched wire.

 

As joe suggested, make sure no wires are pinched. Unplug the gauges, see if the fuse blows. Plug them in one at a time, hopefully the fuse blows. If so, you know the problem is in the gauge. If not, a factory servibe manual will help trace the wires on that fuse.

 

I suggest you double-check you have the correct wires to the correct posts on the tachometer.

I'm trying to get my head around this one >> Fuel gauge reads Full but only 2 gals in the tank, oil & temp read 1/4? Are you saying that is the reading indicated on those gauges WITHOUT a fuse? I'm assuming the answer to this question is a resounding Yes. Because, there should be absolutely zero reading on all those gauges with no fuse. If you have a reading on those gauges with no fuse, then it sounds like you're back-feeding power from some source into the fuse block. Again, check for the correct wiring to the correct terminal posts on the tachometer or remove the tachometer completely and see if the fuse blows.

EDIT: Here's a good thread on Rally Pac setup >> https://classicoldsmobile.com/forums...-wiring-75378/
https://classicoldsmobile.com/forums...uestion-74712/

 

Another tip that I have used before. Use a multi-meter set to ohms, then clip one lead to the load side of the problem fuse holder and the other to a good ground. Than as suggested above disconnect items on the circuit one at a time till you isolate the issue. This will save a bunch of fuses. Mine has an audible setting for a beep when you are alone.

Pat

 

Thanks everyone for the contribution. I will try removing the gauges one by one and see it that helps. I did pull the Ignition Switch which was the original and cleaned it as well but still the same issue. Most likely will just grab a replacement while I am under the dash.

Sean

 

Sean, I think you're wasting money buying a new IGN SW.

"At" the 10A fuse holder. Use a simple test light (or a multi-meter). Measure (Test) each side of the fuse contact terminal receptacle holder (which holds the fuse in place). One side ONLY should have power, the other side should NOT have power. If you have power on both sides of the fuse receptacle holder, that is why you're blowing a fuse - you have power feeding into the fuse from both directions. Eliminate the power source which should NOT be providing power. The power runs in one direction only.

 

While this would work in theory, it most likely will not work in a car. The reason being is if there are lights, relay coils, or similar in the same circuit you will get continuity (ring) to ground. So everything in that circuit would need to be unplugged.

Look at everything you touched/modded. Those are the areas most likely are the cause of your short.

 

Eric, the theory worked well on a short on my 70 A/C circuit. Happened to bump the pull in relay cover on the fender which shorted the coil to ground.
I agree that it may not work well in light circuit.

 

After doing a check on all of the circuit wires and making sure there are no shorted wires I went through and did a step by step check on all sensors and connections (removing then connecting to see whether the fuse would blow). What I found was that the voltage appears to be coming through a short on the gauge pod whereby the GEN signal (brown) was somehow shorting and supplying excess current to the feed on the 10A Gauge-Trans fuse. When unplugging the harness from the gauge pod, no fuse blown. I did buy the gauges second hand and what I am wondering is if anyone has found the circuit boards to be an issue on old units? The next question would be does anyone sell replacement boards for the gauge pod? Ideas?

Sean

 

I sent all 3 of my gauges to Redline and I know that he replaced the circuit board in the tach. The # I have for them is 731 571 0766 and 731 234 3477

https://www.autoyas.com/US/Humboldt/...d-Clock-Repair

 

Thanks Gary!

 

I sent all three gauges off to Redline at the recommendation of the CO community. John received them and found the following to be an issue:

1) Oil Gauge was faulty and causing a short in the circuit (main issue)
2) Pins all need to be replaced
3) Tach has major internal issues that appear to have been caused by someone tampering with the wiring
4) Bulb contact on the tach was broken and causing issues
5) Speedo internals needed to be cleaned and regreased
6) New LEDs to be inserted
7) All housings to be blasted and repainted

I chose to reset the Odometer to zero since this is a full restoration and in reality retaining the original numbers is nothing more than nostalgic.

I should have them back in a couple of weeks and will share the results.

Sean