Alternator Killer now a Fuse Killer


#1

Here’s the lowdown:

'98 Ford Explorer Sport

Nov. 07 - check engine light comes on, battery not charging sufficiently; alternator replaced

Jan. 08 - check engine light comes on, battery not charging sufficiently; alternator replaced

July 12, 08 - check engine light comes on, ABS light comes on, battery not charging sufficiently; alternator replaced

July 12, 08 - new alternator makes it about 10 miles before the charging light comes on, #$%@!

July 15, 08 - charging light was due to burnt voltage regulator fuse in the power distribution box



The battery tests good on a bench test. When driving, everything is hunky dorry until I turn on the A/C and/or radio. At this point, the voltage regulator fuse burns, and I have to replace it. The voltage regulator itself is located within the alternator. My mechanic suggested it might be a problem with the power control module.



Any suggestions???


#2

I looked at some data that shows how your system is tied together and I don’t see any tie to the PCM.

There may be a problem with the main output lead of the alternator to the battery. Place a voltmeter across the alternator output lead and the positive battery post. With the engine running and a reasonable load on the system see what the meter shows for voltage. If there is a good connection there should be less than 0.2 volts across the connection. Also make sure the regulator fuse connection has very little voltage drop on it. If those things are ok then you may need to replace the alternator again.


#3

Look for a short, ie; melted plug ends, worn through wires, pinched harness etc.


#4

Voltage is sensed from the line the 12V alternator fuse is located on. If some other item is dragging down the voltage on this line, the regulator will try to put out more power from the alternator. This can damage the new alternator. Check the main fuses (over 50A) for signs of heating on the pins. There have been reports of bad connections in the wiring causing voltage loss. The simplest solution is to wire the always on 12V to the regulator directly to the battery. Remember the alternator turns on when 12V is sensed on the alternator light line. This definitely sounds like a wiring problem in the main fuse block to the battery.