Do you drive by any abandoned nuclear test sites on your way to work?
Some unusual happenings occur on the instrument panel of my 1987 Mercury Topaz. The red battery light intermittently comes on while driving. This can occur for a short second or two, or for two or three days, and then weeks can go by before it happens again. I've been averaging a new battery every two years. Also, the tachometer occasionally goes in reverse (the needle actually goes counterclockwise), and both the gas and temperature gauges periodically move to the far right past the "full" and "hot" marks respectively. Your expertise would be appreciated.
RAY: Gee, Al, these ARE strange occurrences. The first thing I want to know is whether you drive by any abandoned nuclear test sites on your way to work.
TOM: Actually, Al, I don't think it's that dire. My guess is that your alternator is overcharging intermittently (which is different from what we do down at our garage...we overcharge ALL the time).
RAY: Seriously, if the alternator is overcharging only sometimes, it may be hard to diagnose. But I would suspect a bad voltage regulator; the regulator controls the amount of electricity produced by the charging system. If too much is being produced, you could get voltage surges, which could explain all of the symptoms you describe, except the tachometer going backwards.
RAY: Yeah. We have no idea what that's about. I'd have your mechanic start by replacing the voltage regulator. And if the tachometer still goes backwards, I'd ask the Department of Defense for an advisory opinion. Good luck, Al.