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.

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 curcuit?

Any thoughts?

 

Wow.. this is a new one on me!

I think the first thing I would do is pull the plug off the temp gauge and see what you have on it for readings. One should be switched 12 volts the other should be your ohms input.

Test all wires for power.

Also.. just for grins, take a 12 volt test light and touch it to the gauge housing. Make sure you don't have power on the actual housing.


Willcox

 

I had power to the bottom leg on the temp sender (pink wire) until the fuse blew (I'm sure that was my fault). The center black wire is ground, and the top, green signal wire seems ok and has continuity from one end to the other but not to ground or power. I did have a loose gauge bezel light and socket (half way out) and this may have allowed it to be loose enough that it was making some contact to the gauge housing when I revved the engine up causing extra vibration and giving some extra voltage to the old water temp gauge. I'll try again tomorrow night to see if the light socket not touching helps out. The gauge housing doesn't seem to be getting any other stray voltage that I can tell.

One thing for sure, I need to stock up on fuses...... 3 different fuses blown in the last 3 days, but it is install and testing time.


I rebuilt the entire wiring harness during the rebuild and everything was tested, repaired, new shrink tube, soldered, suspect wires replaced, wrapped etc, so I'm pretty confident in the integrity of the wiring harness itself, but at the connectors it can always be a little scary with the old pieces..

 

Definitely sounds like you have a short somewhere in the mix. Maybe a wire got pinched somewhere, and is charging a ground wire. As you are quickly finding out, grounds are very touchy on the Vettes, and getting a GOOD wiring diagram is critical. Here is a link to a bunch of wiring diagrams, and I've found them extremely useful. Good luck, and let us know how it turns out for you!

http://www.nrjvette.com/johdotukset/?C=D;O=D

 

Thanks,

I have that diagram plus a color chart that I refer to often. I'll eventually get it, just don't want to tear the entire harness out to find the issue.

 

You can test the gauge to see if it's the problem by running 12 volts to the gauge, then run a ground to it. With no Signal, the gauge should go to cool. Then ground out the ohms wire and the gauge should peg. I highly doubt the gauge is the problem.

Now you said you keep blowing fuses. This alone tells me there is a horrible short somewhere and you need to find it. One shorted wire can back feed voltage on the system.

You bulb socket is not the problem. The metal of the socket is the ground so unless it was sitting on one of the gauge post, you can eliminate this as your problem.

Willcox

 

Did you put teflon tape on the sender threads? If so, you may have prevented electrical connection between the sender and the engine block. That would cause your problem.

 

The gauge light socket had come apart so the + post could have shorted, but I did eliminated that as the issue. The blown fuses was because I hit the positive side of the temp gauge wire to ground, so that was my fault.

So now when I push the clutch in the Spal fans go on also, which may have been happening but didn't notice and that would explain the dimming of the lights some. All this is going on with the trigger wire disconnected at the sender end. I guess it is time to retrace the trigger wire or run a new one. The fans turn on with the ohms from the trigger wire, so there must be ground or power getting to the trigger wire somewhere.

Update:
So I separated the two trigger wires, the water temp from the Spal fan trigger wire and that seems to have fixed the water temp gauge issue for the most part. I believe the entire issue is I need to run a separate sender for the Spal and the water temp gauge

I would have run another sender to the other head for the fans, but the plug that is in the head has been there for a lot of years and won't budge and I don't want to strip out the head or break the plug or head. I guess I could get the engine warm and try to see if that helps getting it loose.

Well for now I'm going to buy a thermostat housing that has a temp sender hole. There cheap and I think this will fix things for now. Will know as soon as I get a new housing. Any suggestions on getting the head plug out would be welcome.

 

That was the first thing I checked to make sure the sender was grounded, but that was not the issue. The sender it is dead as can be.