2002 elctrical help

started having weak battery symptoms a few weeks ago. took van to autozone and had battery and alternator tested. result was bad diodes in alternator, so bought and installed new alternator from starter/alternator distributor. everything seemed to be working great. it wasn't until (according to my girlfriend who almost exclusively drives the vehicle) she turned on the air conditioning (or shortly thereafter), that we realized that something was wrong. car starts and runs fine until right around 3000rpm. then ALL the lights suddenly get really bright, the entire dashboard/instrument cluster goes crazy. of course, at that point we let off the gas and the gauges will go back to normal, but different indicator light will remain lit. so at the battery terminals, it reads exactly as it should at 2000 rpm (14.05v) with lights/ac/etc on. then rev the engine up and every time right at about 3000 rpm the voltage at the battery jumps up to 18v and everything goes crazy. disconnected alternator from charging system and started it and ran it with only the battery. ran it up to and past 3000 rpm and no issues with surging lights or anything like that. so i took the newly installed alternator back and they bench tested it and everything was exactly as it should be. unfortunatley the rpm indicator on the machine wasn't functioning so they couldn't tell me if it tested fine at 3000 rpm or not. anyone ever hear of something like this

The replacement alternator is bad. I'm guessing rebuilt, right? I'd go for new, myself, but either way, take that one back and swap it again. Somehow they didn't bench test it throughly because the voltage regulator on the new unit clearly is malfunctioning when you rev the engine.

Bad rebuilds happen all the time. I swear they're getting worse these days, probably due to low cost new parts from China. (If your wiper motor fails, don't even TRY a rebuilt one.. complete waste of time guaranteed!)

thanks for the response. bad alternator was my conclusion also. i mean that's the only thing that could cause those symptoms, right?

they said (reluctantly) they will exchange for another one tomorrow when they get one in stock (even though there is nothing wrong with it as per their bench test.)

i guess my next question would be:

how likely could it be that the alternator was fine but was damaged by some deeper electrical issue with the van?? guess i'll see how it goes with the replacement.

It's extremely unlikely that anything else is the issue, especially given how the symptoms are based on your RPMs. One other thing you could try is having another shop bench test it for you. I'm pretty sure autozone does it. But honestly, I'd just get a new one.

Rebuilt stuff is hit or miss these days, I'm afraid. Hopefully your next one will be better.

update: i exchanged the alternator for another one, installed it and everything's great. so far.

so it was most likely just a bad (rebuilt) alternator. i hope.

Congrats on the fix. Hopefully this one will work better and last a long time.

with all the crazy electrical issues that these van's are (apparently) prone to have, how likely is it that some electrical issue with the van could have caused the 1st new alternator to go bad in the manner that it did? my girlfriend is convinced that the issue with the surging lights and crazy gauges only began after (and therefor because of) running the air conditioning.

No way to know for sure but my guess is unlikely. Alternators are prone to failure. The newest Windstar in existence is now 12+ years old, so it can't be too surprising. Ultimately, time will tell, though, right? Did you at least get a unit with a lifetime warranty?

Fortunately, they're super easy to swap on these. Other vehicle owners aren't so lucky in that regard!