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Discussion Starter · #1 · (Edited)
charge/brake/tail lights come on, voltmeter pegged [solved]

I have an '87 NA A/T, about 128k miles.

On Saturday I pressure washed the engine bay, didn't get too crazy with it but I wanted to get all the dust out of there. I've also had to jump a car that I aquired over the weekend a couple times. I'm thinking on of those things has let to my problem. I've also been using my A/C this weekend and I haven't before.

Last night I was driving in the city and all 3 lights, charge/brake/tail light out, came on and I also noticed the voltmeter was pegged up at 18 volts. So I let off the gas and as the voltmeter dropped down the lights turned back off. I normally get the tail light out indicator going on and off periodically (how do I fix that? <- secondary question) but this is freaking me out. If I shut the car off for a few minutes, I can drive for a few minutes without symptoms. I won't do it when idling, only when I hit the gas. Voltmeter pegs out and all those lights come on. All that red on the dash is cause for concern.

My thoughts were, something with the voltage regulator in the alternator, the alternator itself, or the battery or terminal connections to the battery. The battery is pretty old, and the connections are corroded. I just bought the car about a month ago and haven't had a chance to do that yet.

Sorry for the long post. My car is sitting at my girlfriends right now as I don't dare to drive it. Please help! :bowdown:

EDIT: I tried searching but search appears to be broken.
 

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I'll bet you fried your voltage regulator in the alternator. Grab a multimeter and test the voltages at idle and at 2000+ rpms. If it's not around 13 at idle and 14-15 at 2000+, you've probably got a bad alternator.
 

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Discussion Starter · #3 ·
Nocheez said:
I'll bet you fried your voltage regulator in the alternator. Grab a multimeter and test the voltages at idle and at 2000+ rpms. If it's not around 13 at idle and 14-15 at 2000+, you've probably got a bad alternator.
I'll try that when I get home, thanks.

Is there any way to replace just the regulator? Or is it an all or nothing deal?
 

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apexGrin said:
I'll try that when I get home, thanks.

Is there any way to replace just the regulator? Or is it an all or nothing deal?
I think there is, but it's probably better to let someone who knows what they are doing fix it, or buy a new/used one.
 

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Discussion Starter · #5 ·
Nocheez said:
I think there is, but it's probably better to let someone who knows what they are doing fix it, or buy a new/used one.
Autozone lists the regulator separate from the alternator, and I do all right fixing my own cars. I'll probably give that a try and replace the terminals/clean the battery terminals at the same time. Thanks
 

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Discussion Starter · #7 ·
Is there an online service manual that describes where the voltage regulator is? I was looking for it last night, since that's what I suspected, but couldn't find anything separate from the alternator. I remember seeing a service manual online in the past but can't remember the address now. I'm not driving the car. Thanks
 

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Discussion Starter · #10 ·
Nocheez said:
Well I'm surprised, I didn't realize the Supra had an external voltage regulator.
I'm not so sure it does.

http://www.cygnusx1.net/supra/library/TSRM/ch/CH_06.html

There is something called an "IC Regulator" that appears to be internal, is that the voltage regulator? I can't find anything else that resembles or is labelled as a voltage regulator.
 

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Discussion Starter · #13 ·
Yeah, looks like it's just under the rear cover, nothing I can't handle.

Thanks for the help guys, I'll report back with results later today.
 

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Discussion Starter · #14 ·
apexGrin said:
Thanks for the help guys, I'll report back with results later today.
Alright, so I replaced the IC Regulator inside the alternator and that solved my over-voltage issues. Gauge is stable at 11.5-12.5 volts now in all driving conditions.

However, when I hooked the battery back up, it was dead. :ugh2: I jumped it and drove across town, and it started up fine before coming back. It sat again for maybe 3 hours and again, started fine. This morning though, after sitting about 8 hours, I try to start the car and it's completely dead. While I was replacing the regulator I replaced the connectors for the battery terminals, and I'm pretty sure I did a good job since the car will start fine when it hasn't sit there for too long.

Can over-voltage kill a battery?
 

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apexGrin said:
Can over-voltage kill a battery?
Absolutely. I would change it quickly, before you tax your charging system too much and you get stuck in a loop of "alternator kills battery kills alternator."
 

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Discussion Starter · #18 ·
Bah!

So, the voltmeter in my car is apparantly dyslexic. :wtflol: Even though it was showing an overvoltage, it was actually not supplying enough power. After putting a new battery in, my problem came back. So I replaced the alternator, and now it's fixed. :sadance:

Now I hope the $65 regulator I put in is returnable.
 
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