Hi, thanks for reading my post. I'm a long time lurker, first time poster. I searched for my problems over the forums, and found some helpful things here and there, but they were mostly stories about the batteries going dead over 3 or so weeks. Mine is much faster than that, and I have some other problems as well so I thought maybe it'd be ok to lay them all out here and maybe you guys can help me out. I'm getting on my last nerve!

Truck: 1988 F-250 2 wheel drive, 7.3 Diesel 275,000ish miles.

Problem: History of bad starting in cold weather, now batteries are dead overnight, and the new alternator is overcharging the batteries.

Story: So my truck has never liked starting in cold weather and this fall I tried to help it out with its normal maintenance, and I put in a nice new set of glow plugs as well. That kinda helped, but it still was better with the block heater. (I live in Iowa, so bitter cold and snow, I don't mind plugging it in.)
About a month ago I went out and the truck was dead. So I charged the batteries and took them to Autozone to be tested. One had a bad cell, so replaced it and they said the other one was fine. Next day the truck started perfectly. Great! But only for a day. The next day the truck was dead again! Damn! So I go back to Autozone thinking I must have a bad diode in the alternator or something, and I think maybe they can test it. So they do, and they tell me it's not putting out what it should. So, ok I figure, it's not charging well and probably letting the charge drain back out of the batteries at night. So I replace it, drive around, charge those batteries up and call it a night. The next day, truck starts like a champ - Yes! Awesome! I fixed it! ... For a day. Later THAT DAY I went to start it and it was only charged enough to turn over 'rur rur... click click' NO!! Why?! I had to leave to Michigan the next day, so I figure well, I just won't turn it off till I get there - lol. But wait, on the way up there the alternator overcharges the battery. Urgh!!! With that, I'm not sure if Autozone gave me the wrong one or not. They wanted me to get the 110 (think) and I was thinking I didn't really need that one, but I figure their system is probably right... right?
So I guess I have two problems:
1. Why is my alternator overcharging? Do I need to replace a regulator or something somewhere?
2. Why is it draining so fast?! (Still is after the new alternator.)
I'm going nuts, and I'm a full time student so I'm pretty strapped for cash. But if y'all have any ideas please throw them my way I really need a hand.
I don't have much to test with, a test light is about it. I don't have a meter unfortunately.
Sorry for the novel, and thanks for reading!

 

About the only thing that would drain the batteries overnight was if they were draining back thru the alternator OR the glow plug relay was stuck on. In addition to controlling the alternator charging voltage, the voltage regulator is also responsible for cutting off the line from the alternator to the battery to prevent discharging the batteries. Sounds like the v-reg in your new alternator is not doing either job, I think you should take it back. BTW this is boringly common, you buy a rebuilt alternator from a major national chain and it's no good. Happens all the time.

 

Thank you for your response, I'll be rechecking out that alternator now. And that glow plug relay just in case.

 

If the alternator is internally regulated.
You should change the charging plug to the alternator.
These fail all the time and when shorted internally will kill the battery in short order.

Borg-Warner PT-780
Standard Motor Products S-542
Power Plug 4628011
KEM Parts 350-220
Pico 5711
Dorman/Motormite #85123 / 08622
Pico 5711PT 1981-1989 Ford Alternator Three Lead Wiring Pigtail

Or just swap a 3G alternator and be rid of the fire hazard.

 

Follow the wiring going from the alt. There should be a box on the passanger side fender that the wiring goes to it is the voltage regulator see if autozone can check it. With it over chargeing and draining the batterys it is probably shot. I would get a pic of mine if i could just remember were it is at in the garage.

 

I have to ask Nyxlee, do you have a 1G alternator or a 2G?

Juni, Being they state it's an '88 I have a hard time thinking it's externally regulated, but I could be wrong, I never had a diesel.

 

His rebuilt alternator *should* have come with a new plug which you splice into your existing harness using the supplied butt connectors.

 

An 88 diesel should still be external regulator, the majority of them are into the early 90's. If it is, I'd fire a new regulator at it before I did anything else. I've only had one fail in the last 12 years, but, they do go bad.

 

I did not know that.

 

Thank you all for the responses.
I haven't messed with anything yet (full day of classes) but here's what I know:
-My new alternator came with nothing but new nuts on the posts. No new plug. I have changed many parts on this old truck, and lots of them came out of the boxes with atleast a little piece of paper with minor instructions and other recommended parts to replace. This time there was nothing.

-I'm thinking that it is externally regulated. I followed the wiring from the alt to the passenger side and I see what looks just like the voltage regulator Autozone has listed for my truck.

-I do not know if it is a 1G or a 2G. I checked my receipt and found the part listed online, and all it says is:

Features & Benefits
Premium quality reman, some new components. 100% computer load-tested for all OE specifications to ensure maximum performance & durability. When looking for the highest quality and longest life, look no further than Duralast.
Part Number: DL73031-2-12
Weight: 17.6 lbs
Warranty: Limited Lifetime
Notes: 100 Amp* Without Ambulance package * Premium reman
Manufacturer: Ford
Alternator Amperage: 100 A
Pulley: 2V
Regulator Plug Clocking: 3:00

 

Yeah the new plug thing I was talking about would be for internal regulator. I did not know Ford was still using external regulators on these trucks by the time yours was built.