Mechanics

ALTERNATOR

1999 Ford Ranger

Electrical problem
1999 Ford Ranger 6 cyl Two Wheel Drive Automatic 220000 miles

i just replaced my alternator and battery I had the alt. Checked and it is good. However, it is still not charging the battery. When I test the alternator by taking the negative off the battery the truck stalls. The alternator should be able to keep the truck running without the battery. What should I check next.
Avatar
D.o.c63
March 11, 2009.



A WARNING!
1) NEVER NEVER EVER REMOVE THE NEGATIVE LEAD WHILE THE ALTERNATOR (ENGINE) IS RUNNING!
2)NEVER NEVER EVER REMOVE THE BATTERY NEG OR POSITIVE WHILE THE ENGINE IS RUNNING!

The reason is that without a load on the alternator, the voltage that it puts out is VERY erratic AND can exceed the 14 volts that ALL YOUR ELECTRONICS ARE RATED FOR!
This includes the radio / car computer(S) (PCM/GEM/ABS/AIRBAG CONTROLLER/PATS/ETC.
YOU CAN VERY EASILY WIPE OUT ALLL THE ELECTRONICS AND HAVE A DEAD TRUCK with LOTS OF REPAIR $$$$$$$$$$$$$$$$

Without a field excitation voltage on the alternator, it will NOT put out anything. It may be able to self excite itself BUT the voltage peaks will destroy electronics!
The battery acts like a BIG filter and capacitor to absorb the nasty alternator's output (even a dead battery has this capacity).
************ DONT DO IT! **************

Tiny
Pomonabill220
Mar 25, 2009.