Alternator/Vreg/Gauge charging question.

[lino]

Hey All,

I have a '95 1078 that is showing some odd symptoms...

To start with, I don't use it much (right now), about 10-15 min every couple weeks. I don't have much time to work/play with it, so I keep usage minimal until I understand all its quirks.

So, starting a month or so ago, I noticed the voltage gauge was holding at 24v... This was after I tilted the cab for the first time (which may have been the first time in years). A little digging suggested I may have shorted a ref line to the regulator when tilting. I drove it little, and charged batts externally thru NATO port just in case.

Then a couple weeks ago (after a second cab tilt), I noticed the volt gauge reading 32v, or pegged on gauge. That's even less ideal, but the batteries can handle that for a short time (minutes), so I finished up and parked.
Yesterday, I had a few minuted to check things out so I started by running truck, which started happily enough, and the gauge pegged, right above 32v. So I got out, left it running, and put a voltmeter right on the NATO port.

It read 28.6v.

That's right where I want it.

So, my question is, is there any other voltage regulation devices on the NATO output, or should voltage gauge and NATO port read the same?
That is, it appears I have a bad volt gauge.

Anyone else have a volt gauge fail?


Thanks

ciao
lino

 

[NDT]

Yes. Tap on it and it will go back to 24 volts.

 

[lino]

Yes. Tap on it and it will go back to 24 volts.

That's the first thing I did. Always tap the gauge...

Didn't work though.

 

[NDT]

Sounds like a hard fail. Maybe double check the connections to the instrument and the case ground if it has one (can't recall) prior to replacing it. I agree it is very nerve wrecking to see it pegged while driving.

 

[Suprman]

The voltage at the nato port is the battery voltage. Its a direct connection. If you measure voltage in the cab it should be about 1/3 of a volt less because cab power goes thru a polarity protection box which is really just some big diodes.

 

[Ronmar]

What does the voltage measure at the X1 and X2 test points along the left side of the power dist panel?

 

[aleigh]

... tap it harder.

 

[lino]

... tap it harder.

I thought about tapping it harder, but I didn't have a hammer within reach, so I tried Ronmar's method. At the test points I got 27.7V and at the NATO port I got 28.8 Seems like all is in order (except gauge). After about a 20 min warmup, the gauge was reading correctly.

Thanks all.