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Intermittent alternator failure

I have a 91 Explorer. Periodically the alternator gauge shows that it is charging at a low level and the battery icon on the insturment panel lights up. This happens only when I start the engine. I had the alternator replaced but the problem continues. My mechanic thinks there is a loose connector somewhere. My argument against this is that it only happens in cold weather and only when I first start the engine. It never happens when I am driving. If the alternator is working correctly when I start the engine no amount of shake, rattle or roll will cause it to fail. Sometimes restarting the engine will cause the alternator to work. The mechanic tested the new alternator while it was acting up and the tester showed it was not charging correctly. Do I have a loose connection or does my mechanic? If my mechanic has a loose connection what is wrong with my Explorer - aside from 19 years and a 172,000 miles.

If this ONLY happens during cold start conditions, and the battery is being charged correctly (you didn’t say there are any battery problems), then maybe you should just ignore it.

I agree with you, a bad connection should manifest itself while the vehicle is in motion, or at some time other than cold start.

Maybe the gauge in the dashboard is bad, and there’s nothing wrong with the charging system.

Why spend money chasing this if the battery is getting the charge it needs? If the vehicle starts reliably in cold weather, and the battery tests OK (have you had it tested?), ignore the gauge and warning light. C’mon, it has 172K miles. You have to expect some minor annoyances.

I’m fairly certain your particular model uses an external voltage regulator. Maybe it’s possible your mechanic is assuming the alternator he replaced had an integral voltage regulator instead with the latter being far more common.
It seems to me it was the mid 90s before the internal regulator came along.

Nonetheless, when either an alternator or voltage regulator fails both should be replaced as either one is doing, or has done, the other one in.

The Auto Zone Web site says the alternator contains the voltage regulator. Here are the testing instructions for the alternator:

How old is the battery? Could it be a bad battery positive cable causing high resistance and a conseqent big draw at starting, followed by poor charging?

Suggestion: When the car has been running for awhile, turn it off and check the temperature of the positive cable shielding. If it’s hot, it’s rotten. Replace it.

If there’s a loose connection, it shouldn’t be all too hard to find except maybe due to the shortened daylight and cold.

A look at the O’Reilly and Advance site shows an external regulator up to around 93.
This one looks like the one that was on my Mercury Sable.

Advance also shows this one but on the O’Reilly site it refers to that one as “Exc. Explorer”. The Advance site is not so clear.

Might be a good idea to call the Ford dealer parts dept. in the morning and verify this. Alternator offered several different ways. ???
Ford has also been known to use different A/C compressors on the same type vehicles.

It may not be a bad idea to go out and take a look around on the inner fenders. If a regulator is present then it’s possible that could have been the problem all along instead of the alternator.

This page has a link to other vehicle that the alternator fits. All of them are 1991 to later model Fords. I doubt that there is an external voltage regulator.

If the vehicle does not have an external regulator then the problem would likely be a connection;
Alternator plug loose, burnt, or corrdoed; possibly even the field lead making erratic contact.
Corroded fusible link end at the starter solenoid or a link partially burnt inside.

It’s also possible the alternator (reman?) may be goofy at times. I put a reman on my Lincoln some months back and it dropped dead half an hour later.