I noticed while driving recently in my '75 280Z that periodically the needles in both the oil pressure and water tempurature guages will drop to 0 then after a few moments restore to what I believe is the correct readings. This appears to happen on a regular basis say every 20 seconds or so. Is there a common ground for this instrument? Or could this just be a bad gauge altogether?

As I recall the power to these gauges is regulated by a rather crude voltage regulator that essentially works by turning the voltage on and off peridically, essentially a crude form of pulse width modulation. You can observe this pulsing by putting a voltmeter on the temperature sender connector up near the thermostat.

This pulsing/regulator is done by a little bimetal strip that heats up, breaks connection, and then makes again thus making these pulses. I'm gonna bet that this regulator of yours has a bad connection or is old, or about to break or something like that. Unfortunately, I don't really know where this regualtor is. I suspect somewhere near those gauges and a headache to get at. Probabably can get to it thru the glovebox.

Measure that voltage first. I'm gonna bet you will see zero volts on the sensor when your gauge reads zero as well.

Good luck

Don

Hi,

Spot on wa5ngp. The gauges run on about 7 volts.

I'm 95% sure the regulators are in each of the individual gauges. It's been a while since I last had one apart. Then again, if they're both doing it in unison, that would indicate just the one regulater. Hmm.

Pull a gauge out, there'll be a set of contacts in there that might not be making contact properly or is just plain old. Just be really careful if you open the contacts up to clean them, make sure you don't bend the arms of the contacts as this will affect the spring tension and mess up their voltage setting. I've had success with almost-worn-out emery paper eg. 800 grit. It slides easily between the two contacts and cleans them up really well. Try to get the contact faces as smooth as possible to minimise arcing, which in turn will wear them out faster. Assuming they're not beyond salvation anyway of course. I'll have a look at a couple of gauges I've got here and see which one's got the regulater in it. Watch this space.

Good luck.

Thanks Nacks. I've actually got a replacement guage coming from an eBay purchase. I will though take a close look at those contacts before installing. Is there a testing proceedure for those guages? Maybe with an ohm meter? Or would that be DC voltage?

Does anyone have anymore info on this topic? Is this regulator in the gauge or outside? Also, is there a bench test that can be performed on these gauges?

Sound slike you are getting charging surges. Make certain your engine is grounded and your guage is grounded. Sometimes a weak/low battery will also give your surges.