Hi,

I noticed my check battery light on the other day and happened to be in front of a parts store. They suggested I change the alternator. I replaced it, recharged my battery. The light went out for about 4 hours then back on. I then had my battery tested and replaced with the same results? What are the chances of getting a bad alternator off the shelf? The truck is a 1997 F-150 w/6 Cyl. Are there any other components in the electrical system (IE: Fuses that I need to check?) Are there test points on the alternator for field/ignition voltage? Any help is much appreiciated!
Thanks in advance!

Jerry

Jerry.honeycutt@yale.edu

 

Check the battery and alternator wires to make sure they're not corroded.

 

Check your ground connections at the battery and the starter with an ohm meter. You should read direct continuity (as close to zero ohms as possible. Using a voltmeter, check the voltage at the battery with the engine off. You should read around 12 volts DC. With the engine running at idle you should read between 14 and 15 VDC. Turn on headlights and AC or vent fan on high, you should see a drop in the voltage and then a return to about 14 VDC. Have your alternator (assuming you have an internal voltage regulator) checked at PepBoys or somewhere if voltages are not correct. Also check the wiring from the alternator plugs to the starter relay for high resistance. Also check fan belt tension.
I have changed alternators ( 94 f-150 XLT 4.9) 5 times in five years, but I never changed the connectors at the alternator as Ford recommends. This last time I bought a rebuilt motocraft at NAPA with the plug hardwired in. Seems to be working fine.

 

The chances of getting a bad one off the shelf? Better than you might think. Especially if you buy a rebuild. Or if the kid putting it on or taking it off the shelf dropped it and was afraid to tell the manager for fear of getting in trouble. I used to manage an auto parts store. I've got stories...