WTF is wrong with my electrical system?

lyonsd · 03-02-2001, 07:53 AM

Everything has been working fine for the past few days since I got my '88 Mustang back from the shop.

It's equipped with a 130A alternator from Pep Boys and under-drive pulleys.

If you've ever run under-drive pulleys, you probably already know that the voltage drops at idle, but works OK when the revs are up. And that's the way it's been with my car...until last night.

I open it up on an on-ramp to the freeway. About halfway through it, I notice the "AMP" light come on, as if the car had died. But it didn't die. It was still running just fine. It was only on for a second or two.

On the freeway, I notice my voltage was down, about where it is when the car is idling. The AMP light doesn't know whether to come on of stay off.

With some playing around, I found the following:

The voltage is down at idle.
At 1200-2000 rpm it picks up and looks "normal".
As the rpm goes above 2000, it starts coming down again and the AMP light comes on.

Those are the symptoms. What is the problem?

Bad alternator? Voltage regulator? Something come disconnected? WTF?

Capri306 · 03-02-2001, 03:33 PM

Assuming this is a 3G conversion alternator, check the stator wire (the one all by itself) for a good connection. Then check your grounds. I think a leaky diode can cause the same problem, if I'm not mistaken. I'd take it somewhere to have it checked. Most places will do it for free now, anyway.

------------------
Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch

03-02-2001, 07:53 AM	#1
lyonsd Registered Member Join Date: Dec 1999 Location: Flowery Branch, GA Posts: 236	WTF is wrong with my electrical system? Everything has been working fine for the past few days since I got my '88 Mustang back from the shop. It's equipped with a 130A alternator from Pep Boys and under-drive pulleys. If you've ever run under-drive pulleys, you probably already know that the voltage drops at idle, but works OK when the revs are up. And that's the way it's been with my car...until last night. I open it up on an on-ramp to the freeway. About halfway through it, I notice the "AMP" light come on, as if the car had died. But it didn't die. It was still running just fine. It was only on for a second or two. On the freeway, I notice my voltage was down, about where it is when the car is idling. The AMP light doesn't know whether to come on of stay off. With some playing around, I found the following: The voltage is down at idle. At 1200-2000 rpm it picks up and looks "normal". As the rpm goes above 2000, it starts coming down again and the AMP light comes on. Those are the symptoms. What is the problem? Bad alternator? Voltage regulator? Something come disconnected? WTF?

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Electrical system going crazy?	Nixon1	Windsor Power	3	07-29-2003 08:17 PM
Electrical Surge/Drop	viper5150	Windsor Power	2	08-29-2001 02:16 AM
Cartech/Aeromotive fuel system owners please read!!!!	Black306	Windsor Power	4	06-18-2001 03:39 PM
Electrical Fuel System Prolems. Stumped Please Help!!	89LX50Coupe	Windsor Power	9	06-10-2001 01:01 AM
I have a short in my electrical system, help!	8850	Windsor Power	5	01-14-2001 11:47 PM

03-02-2001, 03:33 PM	#2
Capri306 Moderator Join Date: Sep 1998 Location: Grand Rapids, Michigan, USA Posts: 1,001	Assuming this is a 3G conversion alternator, check the stator wire (the one all by itself) for a good connection. Then check your grounds. I think a leaky diode can cause the same problem, if I'm not mistaken. I'd take it somewhere to have it checked. Most places will do it for free now, anyway. ------------------ Capri306, Moderator, The Mustang Works Online 1979 Mercury Capri, 5.0L -- C4 -- 2.73 1987 Mustang LX Notch