308 QV Instruments go UP when lights turned on

My '84 GTSi has developed an unusual problem. When lights are turned on, the oil pressure, water temp and fuel instruments move up in range about 1/8". The guages on the center console do not change. Engine and battery groiunds are fine. Any ideas before I pull the instrument panel?

Hi Mike, Welcome to Ferrari-Talk !!

Others may share a differing opinion on this, however my take is that the instrument cluster lighting as a whole has insuficient grounding and when the lights are turned on the gauges themselves act as additional ground circuits for the dash light bulbs causing the needles to rise slightly.

As the cars get older and minor corrosion and/or resistance in the wires (ground & hot) builds up it seems to make the problem more noticable.

Regards, JRV

ps: Long Time No See, Hope all is well with you and the family.
pss: for the curious, Mike used to live in Houston 15-20 yrs ago, and I serviced a Beautiful 308B he had back then. Speaking of which...congrats Mike for still retaining the Passion for these finiky but intoxicating machines for all these years !!!...{}

Mike:

If it makes you feel any better, the gauges in my 1985 308QV also register higher when my lights are on. I do not see it as a problem.

This is a most interesting problem...

In the 20 years I've had my BB, the car has always done this. Lights on...oil pressure and water temp rise about a "needles-width" on the gauges. I've had the gauges out a few times...checked and cleaned all the grounds....to no avail.

I suspect that JRV is right on the money with the insufficient ground theory, though I've never been able to pinpoint where the problem really is. I don't believe that the BB or 308 use any sort of voltage regulation for the gauges...If so, that could/would explain the rise in gauge readings...


David

Well thanks folks for the replies...... probably saved me a few hours work to no avail. If I do locate the problem, I'll leave a response.
JRV - good to hear from you and see you are still at the top of your field. Will come by for a visit next time in town.
Regards

Mike

Thanks Mike...

Keep us updated, as this would be yet another small problem to check off the "Ferrari list"

Regards,
David