Electrical Issue Help Needed

I just finished putting the dash in on my 69 rebuild and I am having an electrical issue that not sure what is going on, but it is not good. The car starts and runs fine, everything seems to work on the electrics, except the temp gauge. So I check the sender and it is dead. It was OK when I put it in as it is also the sender for the Spal fans. When I put the ohm meter on, it's completely dead. So I get my old stock sender which works fine and put that in. Start the car and the temp gauge starts out fine, but when I rev the engine, it spins like the devil took it over!

So I disconnect the sender wire and actually pull it as far away from the HEI and other harnesses just in case it was cross talking with other wires. I have the sender on the right side not the left as standard, but that is another story. Well even disconnected the temp gauge spins wildly when I rev the engine.

Well I play around a little, it turns out the temp gauge spinning and also the lights dim only happens when the clutch is in (clutch safety switch engaged). The gauge spinning happens with or without the car running. The lights don't seem to dim when it is not running.

So I'm rather perplexed now as not sure why this is happening and why the draw on the system when the safety switch is engaged.

Maybe the (not used with a manual car) neutral safety switch wires grounding out as they are in the same circuit?

Any thoughts?

Maybe a bad ground at the gauge? I'd sure look at the clutch switch wires. If they are getting to the temp gauge wire and feeding it that could be a problem.
As far as the dimming lights, the alternator should pick up enough to cover that, but it's not dimming the lights when it's not running? Maybe a mixed wire in the charging and temp circuits.
Start unhooking one thing at a time and see what you have to cut loose before stuff starts working correctly.

Get a good solid piece of 10 ga wire, and connect from the engine itself, maybe on the back of the alt at the ground boss, and the frame of the bird cage....

clean all metal to ensure a GOOD connection....

I still have my suspicions over my car having a bunch of crazy buzzy electrical problems just recently...got to scratching my ass as Bird mentioned grounds which I though I been all OVER ....but you know, there was ONE left, bird cage to engine/frame.....methinks after 40 years the conductivity of some bolts is rather suspect....

I have not proved the point yet, that IS going to take some time....but the thing runs SO much better now...

:bonkers::flash:

Thanks for the suggestions.

Well, I think I've tracked it down. I was using the Spal sending unit and trying to run the water temp gauge and fans off the same sender.... I separated the two signal wires and ran just the water temp gauge on the original sender and that seemed to fix it. The Spal will run direct to ground with no issues, so I need to put in two senders. I found that the fans were also running when I pressed the clutch pedal, thus the dimming lights. can't explain everything yet, but at least I'm making progress.

I think I will add a few grounds as it is easy for me to do right now and I have certainly found on some other electrical issues how important a good ground is in these cars.

RobRace10 said:

Thanks for the suggestions.

Well, I think I've tracked it down. I was using the Spal sending unit and trying to run the water temp gauge and fans off the same sender.... I separated the two signal wires and ran just the water temp gauge on the original sender and that seemed to fix it. The Spal will run direct to ground with no issues, so I need to put in two senders. I found that the fans were also running when I pressed the clutch pedal, thus the dimming lights. can't explain everything yet, but at least I'm making progress.

I think I will add a few grounds as it is easy for me to do right now and I have certainly found on some other electrical issues how important a good ground is in these cars.

Click to expand...

The spal sender is a "switch", the temp sensor for the gauge is an RTD. You CANNOT combine them. You were sending 12VDC to your temp gauge.
The clutch interlock is another matter.