Hello, I have a1986 F250 5.8 4X4, my problem is when I don't start the truck for a day or so the battery drains, I have checked the fuses and I was wondering if the tail/park light fuse circut was supposed to always be hot(have fire), even when the switch was not pulled to turn them on, or just which fuses were always hot because I just can't seem to firure this one out. Any help would be greatly appreciated, and thanks in avance to all. JohnB

 

If your battery/batteries is/are on its last legs, it/they can fail to start after sitting for a day without being charged. Quick test would be to disconnect the battery when you shut down the truck, then reconnect when you try to start it a couple days later -- if your battery is drained by then, something's wrong with it, whether or not your truck is draining the battery on its own.

 

Yes, that circuit has power even if the key isn't in RUN or ACCY - you can step on the brakes, turn on the park/headlamps, operate the horn, emergency flashers, interior lighting, maybe a few other things - all without a key.

Art has a good idea for a test; if you want to investigate a persistent drain, one way to find those is to put a test light between the battery negative connection and the battery cable, then go pull fuses one at a time until the light goes out. You will then at least know what circuit has the problem (or where to go looking if pulling all fuses doesn't make it go out).

From Franklin2's images:

 

If it won't light the test light there may still be enough draw to kill the battery overnight if it is a weak battery. In that case you can use a DVM if it has a current scale. Depending on the bulb in the test light it should light with about 200 milliamps of current, so if it doesn't light you'd be safe testing w/a 200 ma scale. But, to be on the safe side start w/the 10 amp scale if you have one.

 

Thanks for all the ideas, I have tried them all but something bothers me and I was wondering if the choke relay, on the firewall by the master cyl is supposed to click when you put the batt cable on the batt, and when I connect a test light between the batt and the neg cable it just clicks. I was wondering if maybe it was stuck or bad, I never noticed a spark that bright whenever I connected my batt before.(all of the batt cable connections I referred to were with the neg cable) The 3 wires that run from the relay are grey, tan/brown, and white/beige, yellow to starter relay, grey to choke term on carb, and tan to alt. Thanks for all of your help and ideas.

 

I haven't seen a choke relay on these trucks, but then I've not been around the '86 trucks, just up to '85. But, I would guess that relay isn't stock. And, in any event it shouldn't click, which probably means it is closing, when you connect the battery cable. It should only click when the engine starts. I think this is the problem.

Which terminal on the alternator is it connected to?

 

Gary, I will check tomorrow to see which terminal the choke wire is connected to, I agree with you as far as the relay being stuck because I noticed that the wire connected to the choke term on the carb had fire in it even though the engine was not running. It only had juce when the engine was running before the problem started. Well today I disconnected ans unplugged and removed the relay, and I will see tomorrow if the batt still goes dead. Thanks for your info and idea: JohnB

 

I think the battery will be fine now. The relay's coil pulls a bit of juice but probably by itself wouldn't drain the battery. But, the choke coil is another story, so disconnecting the two should keep the battery alive.

I'm guessing that the relay should be hooked to the S terminal, which supplies 7 volts or so when the alternator is spinning. That may be enough to pill the relay in, which should then give the choke full battery voltage.

 

I have some troubleshooting here that might help.
Ford Truck Enthusiasts Forums - Grubbworm's Album: Troubleshooting help, for anyone that needs it.

 

Gary, I didn't go out yesterday, but I went out today and just as you said, the batt was still fully charged. I took the relay apart and noticed that when I reconnected the plug to it there was fire all through the relayeverything had 13+ volts, I checked the wire from the alt and it also had 13+ volts, I guess I will just yake the alt off and see if the wire is connected to the "S" terminal as it is supposed to be for the lower voltage. I was wondering if I could just connect a wire directly from the alt's "S" terminal to the elect choke, and do you think the choke coil is burned out since it has been getting full voltage(12+) for a few months, or not. Again thanks for all of your help and ideas: JohnB

 

Grubbworm, thanks for all your help through those pages, they were very interesting and I saw just what I was looking for as far as the "S" terminal on the alt goes. again thanks:JohnB

 

Good! You are getting there.

The S, or Stator, terminal of the alternator gives between 7 and 8 volts, and on '81 trucks is connected directly to the choke coil according to the factory shop manual. However, on Dad's '81 there is no provision in the wiring harness for that, and the choke is plainly marked 14 volts.

As it turns out there are some Ford carbs with 7 volt choke heaters and some Ford carbs with 14 volt heaters. Further, as far as I know, all the aftermarket carb chokes are 14 volts. So, to answer your question, we need to know what carb you have and, hopefully, what the choke cover says. If it is a 14 volt heater then it won't be burned out. And, even if it is a 7 volt heater it may not be burned out. But, you can determine whether it is good or not by placing your DVM in the ohms range, preferably low ohms range, and checking from the tab on the choke to ground. I'm betting it is fine since something was draining the battery and I'm not sure the relay in and of itself would have.

So, before we determine how to fix things lets figure out what voltage your choke is and then go from there. OK?