I've got a 1987 F150, 6 cyl. My volt gauge has been reading in the red, down around 9 or 10. I've recently had the battery and alternator replaced. I took the truck to the auto parts store and they checked out the battery and alternator, both registered fine. I also pulled the neg. clamp off the battery then connected a test light between the neg. clamp and the post, light didn't come on so it doesn't look like there's a drain. Anything else I can check before assuming a bad gauge?

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1987 F150 with 67000 original miles.

 

At night when your headlights are on and the gauge is reading low check to see if the lights are bright or dim. When my gauge drops due to the heater, offroad lights, and sound system my headlights get real dim.

Actually, if your gauge is reading 10 volts that means your alternator is not charging and you are drawing down the battery, in which case after 2 hours of driving the truck will stall. Most likely it is just a bad gauge.

-Jon

 

Thanks for your reply Jon. I agree that it's the gauge just from watching the gauge as the truck starts up. It jumps right up to ten then abruptly stops, turnig the lights, heater, etc. on does nothing to the gauge. If I tap on the plastic covering or push in, the gauge will move up to 12 or 13 but then abruptly stop and just sit there.

 

The easiest way to see if it's telling the truth is to take a voltmeter and check. If your cigarette lighter still works, that's an easy spot to check. Then, see if the numbers on the voltmeter corespond to the numbers the gauge is showing you.

 

I've checked with a voltmeter, doesn't match what the gauge is telling me. I'm virtually certain it's the gaguge. Thanks for your reply.