My 78's battery won't hold a charge, it's a brand new battery as of this summer and I'v had it tested at Oreillys and they said it was fine. Basically it worked fine when I put the new battery in then had a mechanic replace the seals in the power steering gearbox and since then the battery won't hold a charge. I noticed the battery was not holding a charge back in august, I started only being able to start the truck once then when I shut it off I had to charge the battery again to make it start again. I suspect it's the alternator thats gone bad and isn't able to charge when the truck is one. I'm going to have it tested today and see if that's the case but do any of you know of anything that would cause this to happen or what some things to check would be? The battery was fully charged two weeks ago when I drove it last and I went to start it this morning and it was dead again, everything was off last time I shut the truck off so I'm at a loss.

 

Charge the battery so that you can get it started again. Once the engine is running, measure the voltage across the battery terminals and report your results.

 

If you have it running once you get it charged up, you can take it to OReilly's and they can test your alternator on the truck first. If it shows good, there is a small chance that the battery can show good and still not hold a charge for long. I have seen that before when I used to work at OReilly's. However, I suspect that it is your alternator. That is what I would check as well. Good luck with it and let us know what you find out. If you test the alternator and it is good, check your ground wires and make sure that your battery cables are not corroded inside, which I have seen as well. If you continue to have the issue and the alternator tests fine and everything else appears good, speak with the manager at OReilly's and insist on them replacing the battery. They can do it and I have seen a small number of batteries that will show good on the tester, but will refuse to hold a charge for very long at all. One last thing, make sure that you check everything and see that you don't have a power drain occuring that you are unaware of, I have seen that as well with add in car stereo systems and amps and other electrical additions to older vehicles. As I said, good luck with it.

 

Battery cables and voltage regulators have been the most common culprits for me in the past. As fmc said, if your alternator tests okay, test the voltage with engine running with a multi meter. Should be a constant 14.5, I believe. One by one, turn on all accessories such as lights, heat, stereo, etc and watch to see if the voltage stays constant or drops steadily. If the voltage drops to an unusual level, I'd say the regulator is a safe bet. Not to mention much much cheaper than an alternator.

 

If I remember correctly from school, the acceptable charge voltage range is 13.6-14.8.

 

I think you're right. I've always been horrible with numbers, though.

 

I had a problem like this a few years ago. Battery went dead but sometimes didn't. I cleaned every ground connection on the truck, changed battery clamps, tightened alt. belt, did everything I knew to do. Wipers would move slower than normal, dash lights would be dimmer than normal, heater blower would be quieter than normal. It turned out to be the male/female clip that went into the voltage regulator, it was corroded and I was too blind to see it. Sometimes it charged and sometimes it didn't. One hour at a electric shop and $50 later it was fixed. This may not be your problem but it may help. Good luck.

Dennis

 

Have you checked to see if you have a short that would be draining the electrical system?

 

Here's another thought.

I have had this problem with my '78 F-250. Same symptoms, different fix.
After much searching and checking I found that one of the door jamb switches had a "short" to ground. The switch worked fine and I didn't have problems with blown fuses. Everything seemed normal, except my new battery wouldn't hold a charge overnight.

To isolate the problem I removed the (-) battery cable and hooked a test light between the (-) cable and the (-) battery terminal. The test light lit up, with everything off. I then removed the interior fuses, one at a time, and left them out. When the fuse for the dome light circuit was removed the test light went out. I then began reinstalling the fuses I had just removed. The light remained out. This showed the problem was in the circuit with the removed fuse and there wasn't a second problem.
From here it was a matter of disconnecting individual components of the circuit, reinstalling the fuse and checking to see if the test light was on or off.
NOTE: Be sure to have the doors closed, or at least have the door jamb switches in the closed position. If your radio has a clock, or other memory function, make certain it is disconnected also. You will need to disconnect all wires fron the BAT side of the solenoid, except the (+) cable and the cable feeding the interior of the truck before performing this test. This will eliminate those circuits (alternator, underhood light, trailer power, etc.) from the test.
Hope this helps.

Roger Carter

 

Make SURE the battery you buy has the terminals in the same location as the original.

Some peeps don't pay attention, buy a GM or ChryCo battery that has the terminals REVERSED.

Then when they install the puppies, they hook the battery cables up bassackwards.

All batteries sold today are "wet" and may have sat on shelves for years before being sold.

Check the date code on the battery before you buy it, it's on the side of the case (A - January, M - December, last digit is the year).

If older than 6 months = PASS!

 

I have had the same problem, I would let the truck run for an hour or so to charge the battery and the next day it would be dead again, so i decided to put the battery on my charger for a couple days, haven't had a problem since, my truck even sits for weeks at a time and it fires right up.

 

I had the alternator tested today and they said it failed the test so I bought a new 65 amp ultima alternator for $40. I will be testing it soon, the battery is charging and it's deer season opener tomorrow morning so I won't have time to work on the truck much. The guy at oreillys said to also check the wire from the alternator to the battery because it has an inline fuse and to feel if that was broken or not.

I will also be checking the fuses with a test light like mentioned above too. Might as well be sure there isn't something creating a draw. I think for the time being though I will be putting on one of those knife blade switches to kill the connection to be safe. I live 5 hours from where the truck is stored so I don't have a lot of time to work on it and winter is coming up soon here so I need to get it going before the mustang gets parked till spring.

Thanks for the replies, I will let you all know if it works or not.

 

I had the same problem, drove me crazy for about a year. Turned out that insulating the battery from the battery tray fixed my problem. I found out by accident when I got a new battery again and stuck the plastic tray that came on top of it under the battery. Suddenly the problem was gone...

 

Battery housings are already insulated with the exception of the posts on top, obviously. The tray is only included to make the battery taller if needed. Your problem was something else that happened to go away when you replaced the battery. Insulating the bottom of the battery is not what fixed your problem because it alone did not change anything.

 

Just want to throw this in, the alternator in my 78 also would not charge the battery for the past month. I worked on this all month trying to figure out what the problem was, changing many parts and testing many wires. At the same time the ALT light on my gauge cluster also stopped working so today I decided to swap the gauge cluster out for another one that I knew the light worked in. Problem solved, as soon as I did that the alternator begin charging the battery immediately. I couldn't believe it worked