Temp gauge/electrical issue

[mbychows]

Hey, everyone...first post. To give a little bit of background, I bought a 94 GT from a salvage yard this past fall, and it's been my project car in my spare time. The previous owner before it went to the scrapyard didn't take particularly good care of it, but there are no major issues with it, only a TON of small ones. It's been really fun going through and cleaning it up and restoring it back to working condition...it's finally drivable now and I'm working out the minor kinks.

One of the problems that I've been thinking about lately is this: the temperature gauge fluctuates a good deal based on how many power-draining accessories are on. For instance, nothing on = temp gauge at 1 o'clock in the normal range, but lights on, defroster + blower fan on, brake lights on = temp gauge nearly in the red. Anything I turn on causes the needle to jump up higher.

So, before I jump under the hood after work with a multimeter, any ideas?

 

[HISSIN50]

A ground issue can cause the gauge to change with regard to load.

 

[RIO5.0]

A ground issue can cause the gauge to change with regard to load.

What he said... I'd start with removing the Neg battery cable and clean that stud it connects to at the block. Also you have a small copper braided line inside some black plastic tube that runs from that stud to your drivers fender, it also can look ok but be crap... 6 bucks @ Napa for a new copper braided line to replace it. Grind down the body good and re-mount.

You have (2) Green bolt grounds by the battery, scope them out as well.

All your gages are electrical so a bad ground messes with them hard.

 

[mbychows]

Awesome, I'll check it out. Thanks, guys.

 

[5.0_GT_kid]

Been having the same issue with my car.

 

[Bullitt95]

Adding an extra ground wire between the upper intake and the firewall will cure the problem.

 

[89BlackGT]

Check the ground strap from the drivers side frame rail to the left side of the engine block. Mine snapped and caused my gauges to go bananas, replaced it with a thicker braided wire and all was resolved.