I have a 1979 F-350 with a 400 and auto trans. It hasn't been driven on the road for 2 years. A couple of months ago (Winter) the battery was dead so I charged it up. The next time I was going to start the engine the battery was dead again. After a few times of charging the battery and it being dead again I finally went and bought a battery 5 days ago. It was dead 16 hours later. Today I was checking the battery connections and noticed the starter relay was a little lose where it screws/bolts to the inner fender. I tightened the screw that was loose but it's partially stripped out. I was able to tighten it better than it was but my question is this; could the relay not being tight to the inner fender cause the battery to drain? I've had this truck for more than 8 years and have never had a problem and nothing has changed in the last few months/weeks with it, except for the battery going dead.

Thanks for any hints. I'm on vacation next week and will have time to look at it more.

Dennis

 

No, It wouldn't but I've seen a bad relay causing a discharge before. You need a multi meter to check it and other things..

 

I went thru 3 separate new ones from O'reillys before I gave up and went with one from Rock Auto. MOTORCRAFT SW7663. After thinking about it later, I noticed that when I hooked up the POS cable (I think) I had a small spark jump out. Researching it led me to believe that was causing a power drain.

Mine was like yours, it sat for several months and I had a dead batt, same thing as you did, cleaned and charged and finally went and pulled one of my parts truck (400/C6) and it started and held charge for a month until I got the new one from Rock Auto. I put the original back on my parts truck. The Manager at O'Reillys admitted that he has been having issues with his "new" parts and suspects some knockoffs made it in the supply chain. FWIW

 

Other things that can drain a battery are the alternator and/or the voltage regulator.
If you have other electronic stuff, such as a fancy stereo setup, something there could do it, but more often than not a battery being drained over night is something in the charging system.

If you put your hand on the alternator after it's been sitting long enough to cool down and the alternator is warm, you're on the right track.
Hopefully your battery has not been harmed by the deep draining. Even new ones can take a real beating from being dead too often. You could test this theory by disconnecting the main charge cable from the alternator and seeing if the battery stays charged.
This won't tell you if it's the regulator or alternator diode array going wonky, but it will prove out the charging system theory anyway.

Unfortunately you can't usually test the draw with a typical meter because they often have a 10 amp maximum current rating. And often the alternator causing the drain is more than 10a.
Some test lamps can handle more current, but not all of them. If you have a test lamp that can handle it, you can disconnect the battery cable and run the lamp in series and see if it goes out when you disconnect the regulator. This tells you it's the regulator and not the alternator.
Another alternate test would be to unplug the regulator and look for power on the Green w/red wire. If you get any power reading with the key OFF then you have an ignition switch issue.
If you find 12v on the Yellow wire, but nothing on the Green wire, then plug it back in and test the Orange wire. If there is voltage on the Orange wire then the regulator is bad.

Of course, all that is not that important if you're of the mind to change both when one goes bad. Which is what most recommend anyway.

Good luck.

Paul

 

Thanks for the advice. I'll be picking up a new relay since it is always a good idea to have one anyway.

Dennis

 

I do have a multimeter in the garage and I can perform these checks next week. Thank you.

Dennis

 

Voltage reg.

 

My '79 F250 my dad bought new has done this since the time he brought it home. about 3 times a year it drains the battery over night and always has.

The Ford dealer never found the problem and neither did I. but since I replaced the original alternator a couple years ago it hasn't done it since. I'm not sure that was the problem but I'm starting to think so.

 

I changed the starter relay yesterday and the battery was dead this morning. I just changed the voltage regulator and will know tomorrow if that was the problem. The other reg had semi rusty spade connections on it but I suppose if it was bad then the connections wouldn't have been connecting. The clip plugging into the reg look like it could use replacing also due to rusting at the connections. Not horrible but if I have charging issues in the future I'll change it out also.

Thanks for the advice. I'll track this down sooner or later.

Dennis

 

Hopefully sooner for the battery's sake!
The things our batteries go through in the name of testing.
Just replaced one this morning in a 2017 Rav-4 after telling the girls that "oh, it's getting weaker but it might take days, or even months before it's dead completely" Or words to that effect.
Immediately after which the battery took it's last breath and all she had was clicking relays under the hood. When what she really wanted was to get to practice.

Hmmm, gonna' start building that dog house sooner than I had expected...

Paul

 

Everything I've read says automotive start batteries don't like deep discharges at all, even once, the claim is that somewhere around a half dozen discharges (below 11 volts) and it's ready for the scrap heap, battery is toast. This is why start batteries don't work too well when pressed into "marine" or deep cycle applications like trolling motors.

 

Not trying to stomp on toes here, but isn't there a better method for finding battery drain on the system?

IIRC, parasitic draw test is one of the best methods to determine where the draw is coming from.

I'm not a wiring guru, so I'll let someone else explain it:

 

Not stomping at all. There are definitely better ways than just draining the battery.
I think we touched on them at the beginning, but never got into much detail and I'm not necessarily the one to add the details anyway. So yes, definitely thanks for adding some details.
Now I'm gonna' have to go watch another YouTube video. But hey, this time it's got a George Clooney look-alike! So how bad could it be, right? Might be some beautiful women and exotic locales added for effect.

Paul

 

Probably has much to do with price too, because a very inexpensive battery I put in a friend's Jeep a few years ago only had two discharges in it. After the second one (total time, three days) the battery would not come back to life under normal charging methods.
Might have been saveable with the right time and tools, but this one went back.

So that certainly lends credence to what you were saying.

Paul

 

I just went out and started the truck. It fired up perfectly. I guess it was the voltage regulator. Thanks for the help.

I'm glad I didn't take the old battery in for a core charge yet, it's probably good and it's a very large semi-truck battery. I had just refilled it with sulfuric acid and would hate to waste it.

I will check out that youtube vid when I get a chance.

Dennis