Hey everybody. My '65 F-100 (352 V-8) is having an electrical problem of some kind. Long story short, the battery is draining in less than a day unless it is unhooked every time it is used. The power loss happens overnight if the car is sitting and once power has been lost once, it can hapen while driving as well. I have tested the wires I can see and I don't see any obvious drains (e.g. line to the starter is not drawing power), but I haven't gone top to bottom. I'm going out now to have the alternator tested.

Does anyone have a checklist for diagnosis of a problem like this?

Also - has anyone replaced the starter in this engine? Looks like a beast, but I could be wrong.

Thanks!

 

Does it always drain overnite, or is it a hit and miss problem? Sounds like the charge system since it happens while driving also. Like your alt isn't always charging. Otherwise it would be a direct short to drain the battery while the alt is charging.

 

Get yourself a light socket from an old car, make sure it has decently long leads and a working bulb. A backup or turn signal socket is usually pretty good.
Remove the negative battery lead. (I recommend the negative lead because it is easier to run these tests with it, as usually the negative lead is just one large wire to the battery. There are several to the positive cable, which can make it a bit more difficult.)
Lightly clamp one of the light socket leads to the battery post.
Affix the other socket lead to the negative clamp. This will put the bulb in series, and will light as long as you are drawing juice. Make sure the bulb is between the battery post and the negative lead.
If you have a drain, the bulb will be lit. If the bulb is not lit, there is no drain.
This is important! If there is no drain, then the battery isn't getting juice to be charged back up, or it will not hold a charge. Most likely causes for this are corroded terminals, corrosion in the cables (hard to see), a bad alternator or a bad regulator.
If it is lit, then start disconnecting wires to discover the source of the short. Disconnect only one at a time.
When the light goes out, you have found the source.
I would disconnect the positive lead at the alternator first, then the connector at the regulator.
Do you have an aftermarket electric choke?
How about an aftermarket radio or gauges?
Check for brake lights or aftermarket gauge lights staying on too.

Good luck!

 

I chased a slight drain on my 64 F100 for a few weeks. The culprit was the trailer electric brake controller.

 

I agree with all of banjopicker has to say. 12 volt test light with probe and aligator clip other end will also do. Don't probe any wires, hookup as banjo describes. If your truck has interior lights that go on when doors open, make sure doors are closed as anything that is on is going to light the test bulb. A later style radio with clock memory will light the bulb. Before disconnecting any wires, pull the fuses from the fuse block one at a time and see if the light goes out. As the electrical system in our slicks are simple by todays standards, shouldn't be to hard to find. I'd put my hand on the voltage regulator and have someone turn the key on an off(dont start engine) a few times. You should feel a click as relay opens and closes, if no click relay could be stuck on and keeping the alt energised all the time. You'll find it, good luck

 

My dad had the same problem with his 66 4x4 took my 66 4x2 and put them nose to nose and ran checks and swapping out bits and pieces till i found that the fuel sending unit was not ground out even with the key off and no reading on the gage with the key off it was still drawing power. took a piece of wire and put it to one of the bolts and ground it to the back of the cab no more power draw.

 

Looks like you already have some great advice to find the trouble. The test light will not lie. This summer I had a similar problem and chased it to the alternator. The alternator would charge, so it tested out akay, but when it was not running it would puke it's guts! Found the trouble with a test lite! It is not surprising when you think about where most alternators come from these days. Not to knock the countries of origin but things are put together as cheaply as possible by the guys that wear the suits and make the decisions!

 

Unplug voltage reg and see if still drains battery overnight. Had same problem once.

 

jsut aanother thought. if your test light lights up you can start removing fuses one at a time and hopefully the light will go out before you run out of fuses. at least it'll narrow it down to a specific area. mine ended up being the pressure brake switch on the master cylindar. it was shorting out just enough to drain the battery. i also used one of those 10.00 voltmeters as it gives a little better reading than a light bulb. good luck. Dutch