Recently I noticed my dash voltmeter reading low- like under 10 volts!

It was at night with lights on, but not much else, at idle.

I came home immediately thinking I lost the Alt and was running on the battery.

which was not the case, the car continued to run fine with the battery ground disconnected. I took voltage measurements and at idle, all accessory off, Im getting 14.1 volts at the jump post under the hood and off the starter. turning on the AC and the lights, it goes down to about 12. the gauge reads about 10.5-11.

So its consistently about 1.5 V low. Why could this be? I checked ground point directly under the steering wheel- good. I cleaned my engine grounds and main the battery ground. and fuses for the instruments and lights.

I dont think its been this way all the time...nothing electrical has been done/touched lately.

Could it be the contacts on the back of the cluster?

Car: 81 928 58K miles

 

I think there is an adjusting screw on the back of the meter.

 

Warning dont run the engine with the ground strap disconnected,
major damage to the electrical system will result.

That said there is an adjuster inside the gauge pack,
it requires the pod be removed then the gauges removed from the case,
then next to the alt gauge there is a rheostat.

Put a towel down then lay the gauges on it,
then with them connected , run the engine and set the meter .

NOTE use a multi meter to get an accurate voltage reading at the hot post.

Add some deoxit to all of the connections,
your pod will work better and the lights should also be brighter

 

What Stan said - Do not ever disconnect the battery ground when running - on a modern car it is not in any way a meaningful test. You can easily measure voltage with a DMM as you ultimately did to determine if the alternator in generating. This is both quicker to do and more meaningfull, stay away from the shade trees...

Without the battery in circuit the alternator voltage regulation can be horrible, massive voltage spikes are possible - the kind that kill old electronics.

If you really see only 12V with just AC & lights you may need some connection cleaning and/or a new regulator...? It sounds weak.

Alan

 

Hey Mark good luck. I need to pull my pod soon and do a bulb refresh and contact cleaning, fuel gauge adjustment, voltage gauge adjustment, etc. Get some Deoxyit if you don't already have some. Treat all electrical connections.

 

the red dots on edge of the meter are mine, just dividing the space between the 12 and 14 to find 13.75.
attached leads from the output of a battery maintainer to get a known voltage input (Fluke meter inset).
my volt meter read 1 VDC low. use trim pot (circled) to adjust


as close as i felt like getting it. it doesn't need to be *that* exact.

 

Great pictures Dave, thanks for posting them.

 

Thanks, yes a picture is worth a thousand words ,
I just did this adjustment to my 85 Euro it was reading quite low even after the deoxit treatment,

the lamps were very bright though ,
as I added few drops to the rheostat on the bulb illumination controller

 

Ditto

 

Thanks for posting the pics.

 

thanks everyone. didnt know about running the engine without battery was an issue. Learn something new everyday.

 

there was text with those pics that didn't post for some reason...

 

which was?

 

I'm running metric volts, they're smaller so when the gauge runs between 7V and 9V all the time it's ok.