[DeTomaso] Temp Gauge Rise

[MikeLDrew at aol.com]

In a message dated 4/27/10 4 05 18, wdemelo at cogeco.ca writes:


> Another fellow on the PI board has reminded me of a similar problem I'm 
> having. My temp gauge rises considerably ( 15-20 deg) when I raise my 
> headlights. I was thinking it was induction in the wiring, but I beleive the 
> headlight switch only carries the current of the relay coil, which is minimal.
> Any suggestions?
> 

We covered that here in the not-too-distant past; I may have even asked the 
question myself.   It's a rather common problem (my Pantera does it too).   
You'll note that all the minor gauges except the ammeter are affected the 
same way, to varying degrees.   Your fuel gauge will go up too, not as much 
as the water temp gauge, and the oil pressure hardly goes up at all.   

And strictly speaking, it's not the headlights that do it; the gauges jump 
when you move the headlight switch to the first position (interior 
lights/marker lights).

Evidently the cause is inadequate grounding of the gauge lighting circuit.  
 There is a single ground wire circuit which runs daisy-chained from one 
gauge to the next to the next, and then eventually finds its way to the single 
ground stud on the back side of the battery ground stud.   Bill Taylor 
suggested that running a second ground wire directly to the chassis might sort 
it out.   I have ambitions of doing that to my car shortly.

It should be fairly easy to cut off the connector at the end of the daisy 
chain, then install a new one with two wires attached, and run that second 
ground wire down to the chassis, drill a hole and secure it with an eyelet 
connector.   Making the wire a few inches longer than needed will enable me to 
pull the panel forward for servicing etc.

I may even try to do this in the next few weeks; I'll let everybody know 
how it works when I'm done.

Mike