Last night at a stop sign I noticed my 96 (CTD w/auto) headlights got a little dimmer. Once the rpm got above about 1200 they were bright again. I looked at the voltmeter and at idle (750 rpm) its about 12 volts and as it revs past about 1200 it's just a bit over 14 like normal. I know it's not the grid heaters because those have been disconnected for a couple years now but the voltage swings look similar only based on rpm versus cycling of the heaters. The NAPA guy hooked up his "tester" and it said "charging system problem;" great help.

I guess my question is: Has anybody seen this before and what was the cause?

Other than this the truck runs great.


I'm just hoping it's not the PCM/regulator. A NAPA alternator is 130 bucks plus core.

thanks, cd

 

Funny you should post............ Brownie never did that, but since day one Greenie would do the same thing. I ran that way for about 2 years, it never did not charge the batteries, it just did not keep up. Finally this March, out of the blue, my Alt. light popped on.

Went to Napa, got their best new unit, changed it out, and problem is gone, no dimming, etc.

Bet your situation is the same, Alt. just getting weak.

LOL, I got my last dime out of mine........

 

most likely brushes in the alternator, they are easily replaced and cheap(10$ or less) classic symptom as you describe above.

remove alternator remove tin cover, brushes are in an holder assy held in with 3 phillip head screws, after remocing you can see the slip rings, they can have a wear ridge, but they also can wear completely out, if they are worn thru brushes wont help, my orginal alternator went thru 2 sets (slip rings still good) I replaced the alternator but kept the core and put a 3rd set of brushes in it, and it now rests behind the seat, in the event I need a replacement on the road

 

New set of brushes and it's working like it used to. 11 bucks at the parts store and a pretty quick fix to boot. cd

 

Make sure it's not your grid heaters coming on before you replace anything.
Easy to do, just remove one of the small wires off of each of the two relays almost under the driver's side battery.
They just pull off, no tools necessary.

 

glad to have helped