Mechanics

BURNING THROUGH ALTERNATORS

2002 Mercury Marquis • V8 2WD Automatic • 75,698 miles

2002 mercury grand marquis.

I have burned out 2 reman alternators in 2 days. When driving one would put out 17 volts the other puts out about 13.5 but wont charge a new battery, they both would screech like they are dying and were remans from 2 different manufacturers. I figured a short somewhere could be causing this.
After removing fuses I noticed that when I remove the fuse in my power distribution box that is marked "Generator, Starter control relay, fuses 15 and 18" the alternator will run much quieter, the load on it is quite less. Fuse 15 is my ABS and removing this does not change the noise I can hear of how hard the alternator is running. There is no fuse 18.

Maybe I just had bad luck with reman alternators but I think I have a short in my starter control relay. The car starts fine when I have this fuse in but the alternator is obviously under a much higher load with it.

Where is the starter control relay at? It is not inside my distribution box so I am wondering if it is mounted on the firewall somewhere?
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Coralzombie
August 13, 2011.




O.K. Going to need to do some testing Do you have a Digital Volt Ohm Meter? And bacis knowledge of electronics?


Docfixit
Aug 13, 2011.
Yes and yes. I have tested the alternator. With this fuse out it put out 12 volts when car is off so does battery. When car is on with this fuse off it puts out 13.5 so does battery. When I put this fuse in the alternator acts as if it is under a heavy load. I am sure the current is increased but I dont have an amp clamp. The nearest I can figure is that something on the circuit to my starter relay is causing the alternator to work harder. I can't find this relay by following the wires from my starter I think it may be on the firewall behind the engine not sure though
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Tiny
Coralzombie
Aug 13, 2011.
It may be that I have just had bad luck with alternators but A new one wont be in stock until monday afternoon and they parts place suspects I have a short that is causing my alternator to work harder. They suggested I use an amp clamp on the alternator wire. The amps should drop below 40amps after car has been running for 1 minute with no lights, radio etc. But I do not have an amp clamp.


Tiny
Coralzombie
Aug 13, 2011.
Pull plug on ALT see diagrams one will be yourskey on connect volt meter from TERM "A" to BATT POS does meter read.5v or higher?


Docfixit
Aug 13, 2011.
Forgot pics


Docfixit
Aug 13, 2011.
When running or when car is off?


Tiny
Coralzombie
Aug 13, 2011.
Just key on all fuses installed


Docfixit
Aug 13, 2011.
Reads 3mV .003 Volts DC
Key on all fuses installed.


Tiny
Coralzombie
Aug 13, 2011.
Now OHM chcek from ALT body to engine and NEG BATT terminal what are readings?


Docfixit
Aug 13, 2011.
Starter relay in high current box on left fender behind fuse box and blower motor


Docfixit
Aug 13, 2011.

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