Electrical Question

[348tripower]

My gauges change when I turn on the headlights. The temperatue gauge shows hotter. Is this a ground problem?

[enjenjo]

probably. You have a dedicated ground on the guages?

[wayne petty]

got a digital volt meter with clips on the ends of the test leads..

lets spend 3 minutes and do some voltage drop tests on the ground side ...

set digital volt meter to 20 Volts DC..

start the motor...   turn on the head lights...

test from the negative battery terminal to the engine block.. 0.04 volts is good..

test from the negative battery terminal to the body..   0.02 volts is good..

test from the engine block to the body.. 0.02 volts is good..


that should have taken perhaps 2 minutes..

another 2 minutes... under the dash board...

test from the dash board to the body...    you should have almost no reading.. 0.02.. maybe 0.01...  

test from the gauge ground  to the body.. 0.02... or 0.01...

why.. ben franklin got it wrong.. electrons flow from negative to positive..   so if you have a bad ground somewhere..  you will not have enough electons to work the circuit..    

the build up of electrons is what voltage is..

these voltage drop tests can tell you where the gremlins are ...  in seconds...

best of luck...

oh.. and remember.. the headlight switch is usually grounded.. through the mounting screw to the dash board... some cars.. mount it through plastic.. and have a thin steel plate... this has to be properly grounded. for instrument cluster resistor to properly work.. (the big ceramic thing with the coil spring embedded in it... mounted towards the front of the headlight switch..)_..       if you can get a clip onto the metal frame of the  headlight switch.. turn the switch on.. twist the dash lights to full brightness.. while the other test lead is grounded to the body... you should have again.. 0.02 volts..

why such a small reading..   if you have more.. you have a ground problem...  dirty connections.. loose connections..  missing connections..

when you have gauges that move when you turn on the lights.. it is always a ground problem somewhere ..

feel fee to ask questions.. i am full of it...

[WZ JUNK]

I had the same problem many years ago on the old truck.  Skip Readio told me that it was a ground problem.  I added a large ground strap from the engine to the frame and another from the frame to the body.  It cured the gauge fluctuation.  I vote that you have a ground problem.

John

[38HAULR]

As well as proper grounding, make sure you have  a correctly operating voltage reg for the gauges,these maintain a constant voltage  of 5volts..

This is a design feature for the gauges stay to  constant regardless of voltage fluctuations in the system .
Two or three yrs ago on a hot summers day in traffic I noticed my Mustang temp gauge just about peaking, I pulled over and found no actual boiling I then also noticed the fuel gauge giving more fuel than I figured I should have had,and the oil gauge up higher..
The reg had crapped out.
These are a bimetallic device that actually pulse giving an average voltage of 5volts.
I replaced this with a pair of 3 leg, 5 volt 1amp regs from an electronics store wired in parallel,total cost was around $3.
Frank.

[OldSub]

You have a voltage drop problem.  It can be caused by a number of things most of which I think have been listed.  I'd start with Wayne's trouble-shooting and figure out just what is causing the problem before trying to fix it.

[348tripower]

Thanks for all the suggestions. I have been spending all of my time block sanding the COE. I will be on vacation the week after the 4th and I will do the testing and add ground straps. I will report back then.
Don

[papastoyss]

I used to work at a Porsche dealership. When they came out w/POS 924 in the late 70's the dash grounding was so poor the temp gauge would wiggle in unison with the turn signal flasher clicking.Running a ground wire to the battery cured the problem.