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MG MGB Technical - Headlights brighter at certain times

Sometimes when I am driving both my headlights and interior lights will seem to get a little more juice forcing them to get brighter. I assume there is something going out. Has anyone else seen this behavior. This is occuring on a 76B.
Josh

Once the engine is running over about 1500 rpm the lights should be at a constant brightness unless you add some significant electrical load like heated rear window, stop lights, turn signals, which will make them a little dimmer. If your lights are dimming and brightening at a constant load and speed then it indicates bad connections somewhere or the alternator on the way out. Is your ignition warning light working correctly? If not you could be intermittently losing charge and not know about it. I would hook up a multi-meter for a while and watch what is going on.
Paul Hunt

It seems to not be consistent. Sometimes it's at idle and sometimes it's at speed. It doesn't seem to be related to what the rpm is running at. What is the best way to check the alternator with the multimeter?
Josh

Measure the voltage between a brown at the fusebox and a good ground. You should see 12.7 or so with the ignition off and a good battery, a bit lower than that with the ignition on, and 14v + with the engine running at a fast idle and minimal electrical load. With max factory loads (i.e. no mega-stereos) this should not drop below 13v.

BTW, I assume you have checked that the fan belt is correctly tensioned.
Paul Hunt

funny you should say that. I recently replaced my belts on the B and have been having a hard time getting them to adjust correctly. I know I should be between 1/8 and 3/8 in flex but I have had them for about 3 months now and I have had to re-tighten them several times because they start squeeking. For instance last night I went out and tighened them and they were like 1/2 and inch of flex. Bad stuff. So to sum it up they have been tensioned but the belts seem to still be streching every once in awhile.

Josh
Josh

I've always (many cars, even more years) reckoned on about 1/2" but not found it critical anyway. If the old belt was OK I'd say you had a bad one now.
Paul Hunt

This thread was discussed between 27/09/2002 and 01/10/2002

MG MGB Technical index

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