Installed this gauge a few years back (using tips posted here on Brickboard) and have enjoyed monitoring my charging system until recently, when the needle started creeping up ever higher. Now, its all the way on the east side of the high red zone. I checked the voltage with a handheld meter; at the battery 12.something with engine off and 14.something running while running, which seems normal. My question is: is this a normal failure mode for the gauge? (its a junkyard volvo part.)

FYI: I've had multiple used stock Volvo voltmeters give improper readings.

VDO still makes a voltmeter in the same size as used on the 240 and is available from Summit.

https://www.summitracing.com/parts/vdo-332041/overview/

I'm guessing it isn't a common failure, or I'd have seen something about it before posted here in the past 18 years. The gauge has a device inside to create the expanded scale which uses a voltage reference diode (zener), so if that device became electrically leaky (or the circuitry got moist) the gauge could start reading high.

They're such nice gauges I've never taken one apart. I'd figure they were pretty well sealed against moisture, but there is the lamp opening. Water follows wiring. Best be on the lookout for a replacement; they are useful gauges. If you've got a w/s leak make sure to leave a drip loop in everything you wire yourself.
--
Art Benstein near Baltimore

"Stop spinning your wheels in the quagmire of the subjunctive" -Phuc Tran

Thanks for the input. I will start looking around for a replacement.

Is this a Volvo of aftermarket?

It is displaying hi voltage so it is not a connection somewhere.
--
Paul NW Indiana '90 745 turbo 145 K

It is the volvo gauge.