Temp Gauge & tach jump - why?????
 

Hello, having some elec gremlins and could use direction/suggestions...

71 Lemans Sport, 350, stock harness.

Thought car was running hot and didn't trust just the warning light in the dash so I installed aftermarket electrical (numbered) temp gauge. Every time I step on brake, hit turn sig, lights, heater blower fan,etc - the gauge jumps up. Noticed yesterday that it appears in the tach as well but it usually drops or bounces around. Happens on both gauges when I hit/use any of the above mentioned items( brake, signals, lights,etc).

Battery does not drain when the car sits.

Any suggestions?

Could this be a short to graound on a main power wire feeding the fuse box? If so what color is that wire and where should I start traceing it from?

Any help/suggeatins are greatly appreciated. :confused:

It's a voltage supply problem. Turning on accessories is using up most of what's availble in the circuit you're tied into for power. Could be that you're using a low amp small wire circuit or charging system isn't up to par.
It is something that you see quite a bit of on these cars. Worse on some than others. More prevalant on cars with external voltage regulators.
Might want to try taping into a stronger power source. Like the larger ignition & accessory wires coming from the ignition switch.
It'ld still be a good idea to do a voltage check and see how well the charging system is working.

Check the grounds too. May want to load test and voltage drop the power and ground circuits. :)

thanks for the replies. Did not have time to mess with this over the wknd, however I have been reading through the other posts here as well to learn as much as I can.

Just an FYI. The only things non stock I have plugged into my fuse box are the switched power for my (Alpine) stereo, and switched power for the temp gauge.

Battery has top and side terminals, so I went from the side terminal connection through a fuse block back to the trunk to power 2 amps. Not big amps though.

My alt is old and a bit noisy. I think my first plan of action will be to disconnect all stereo equip, and pull the alt and get it tested. Then reconnect the alt but no stereo and see what happens w/the gauges. I don't know how to do a voltage check, but I do have a meter so if I can figure it out I'll do that too.

Thanks again, I'll let you know what happens next.

Progress!
 

So, last night I replaced my alternator with one that I had tested and was good. Also fixed a few iffy connections and the 30amp fuse behind the alternator. I pulled my ground wire from the battery to the engine and cleaned the connection. Also ran another ground that I made with a spare neg battery cable, from the same grounding point on the engine to the body of the car at the front inner fender well/battery tray.
Started it up and flipped switches/brakes/signals. No fluctuation on the tach. Hooked my temp gauge back up at the fuse box and tried again, it did not move either.

Still have to hook my stereo and all back up but I want to do this in steps so I can isolate the problem if it still exists.

I am going to drive it aroud some today and see how it does. I quit right then last night while it seemed to be working so I could go to bed feeling like I accomplished something:)