I NEED HELP!!!
I have an '89 F-150. My alternator does not charge my battery. At first I thought it was my battery not holding a charge. The truck ran fine when I jumped it or roll started it so I know that the alternator is putting out juice. So I replaced the battery. But after I drive it for a while and shut it off, the battery is dead. How can the alternator be putting out juice, but not charge the battery?!? I had checked some wiring the other day - there are three wires coming from the alternator that were all tied into one wire going to the starter selenoid and they were corroded and cracked to I cleaned them up and retied them together but that doesn't seem to help. Does anyone have any suggestions?

 

had the same problem. should be the connection you have w/those 4 wires

 

http://cartalk.com/board/showflat.ph...&Number=204595

I have experienced a similar problem with my '91 F-250 4x4. Check the link above for the response I received on the cartalk.com forum.

In my case, I could get a jump start and verify my battery would charge. But a while later, would have a dead battery again. Replaced the battery, but did not help.

Sounds like there is a transistor in the regulator module for the alternator that controls when the stator (field coil) is drawing current. In my case, I can measure about 4 amps with the key off; this quickly drains the battery.

Good Luck!

 

I'm starting to suspect a similar problem.

My battery tests out fine (Load Tester) and works fine during the day. With the truck off, I get 12.? volts at the battery. When I start the truck, I get around 14 volts at the battery. I turn on the lights and accessories and the voltage stays up around 13-14 Volts.

At night, The truck runs fine and the Volt Guage on the dash stays up where it is supposed to be. However, If I Idle for a little while and then turn off the truck, the battery barely has enough juice to start it.

I'm starting to suspect that the alternator is not putting out enough amperage to keep up with the truck, lights, and recharging of the battery at idle. But I don't see that on the trucks Volt Guage, or on the digital Multimeter I Tested with, If that was the case, I would expect to see the voltage drop when idling with the lights and accessories on.

 

I had the same problem with my truck, I just broke down and replaced the altenator, and its been runnin fine ever since, It kinda ticked me off though, because I had to replace one of the clips to keep the warranty on the new altenator, but at least my baby is back on the road

 

well, I think I fixed my problem...

I started the truck Hooked up a multimeter to the battery...14.4 Volts

Then I turned on all the accessories I could find... Lights, Fans, Wipers, Radio, hazards, ETC, ETC.

and watched as the votage dropped... 13V... 12.7... 12.3..... 12.2... 12.0... UNNACCEPTABLE

I went to jiggle the cable from the alternator and noticed that the cable from the alternator to the Starter Solenoid was very HOT. Especially near the Solenoid.

I looked closely at the cable and realized that there are three Cables that come from the alternator. Two thick ones and a thin one. All three go into one side of a fusible link, and there is one thin cable that comes out the other side of the fusible link and attaches to the hot side of the starter solenoid. So all of the current coming off the Alternator has to pass through this "Funnel"

I was convinced that the thin cable was just too thin to handle the current (Even though it looks like it came that way from the factory.

I cut the three cables where they go into the fusible link and attached them directly to positive terminal on the battery.

Fired up the truck with all accessories on and now it held steady at 13.X Volts. And the wires stayed cool.

I know that by bypassing the fusible link I run the risk that if the alternator should ever short to ground, I'm going to have some burnt wires (at best) but I'll come up with some other way of protecting it in the near future (High current fuses or something)

 

why dont you just run an inline fuse in the hot wires, that way if it gets too hot, the fuses will blow and it will shut down, I mean it woudl be better than having to do massive rewiring

 

Well, I tried replacing just the regulator module this weekend. When I installed the new regulator module and checked everything with a meter (ignition key off), I was pulling < 20 mA to the alternator. I started my truck up, let it run for a while, checked output voltage (just over 14v with the alternator running), stopped it, checked the battery (just over 12v) and decided I had fixed it.

Jumped in my truck later that night to go to work and had a dead battery again. Testing it the next morning, I'm back to pulling 3+ amps to the alternator regulator.

All I can figure is that when the original regulator failed leaving voltage on the field (until the battery was completely dead), I may have partially shorted the field coil. Since my truck wasn't running at the time, the cooling fan on the alternator wasn't cooling but the field was heating up. If I partially shorted it, it may pull too much current and have burned up the new regulator.

Just theories. Probably time to replace the entire alternator.

Out of curiosity, does anybody know what the field coil resistance should measure?

Thanks!

 

I usually let it vary between 3-10 ohms. I'm not too picky provided there are no shorts or opens in the field (Stator) winding. More than likely you blew a diode in the rectifier and it's leaking back thru the field windings causing them to heat up and draw even more. Go down to your friendly neighborhood alternator/generator shop (look in the yellow pages under automobile) and get a HD rectifier, new brushes, and a new voltage regulator.

Make doubly sure that you have some heat sink grease handy. You're gonna need it for the back of the rectifier and the edges of the Voltage regulator.

Clean everything including the case with electrical cleaner (CRC sold at store). place a slight smear of heat sink grease on the ENTIRE BACK of the rectifier and install. Do the same for the Voltage regulator even tho it mates only along the edge.

Put the whole thing back together, change out the bottom plug on the harness with a new one (better construction and is more heat resisitant).

One heck of a lot cheaper than getting a re-built (kludge) at the auto store.

Been overhauling mine now for over 30 years. Only had to replace one (1995 ASTRO) and I made sure it had a lifetime warr.

Larry
Larry