Need help with electrial problem
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Senior User
Joined: Sep 2009
Posts: 104
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From: Pittsburg KS
Need help with electrial problem
Ive been fighting an electrical leak somewhere on our F350 for awhile now without any success, Ive got some time off school now so hopefully I can figure it out. Just a quick rundown of the issues, Problem started a few months ago, noticed that the headlights were not working, cab lights and dash lights still work fine but no head lights. After I noticed that I noticed the batteries were slowly getting weaker and weaker until finally no start. I pulled both batteries and replaced the positive battery lead, it was in pretty bad shape and I figured it couldn't hurt. Put the batteries on a trickle charge and they held a charge fine for over a month just sitting on my shop bench before I could get them back in the truck. Once I put them back in truck (and got my problems with the new starter lead straightened out) the truck started and ran fine, let it sit a week and batteries were dead. Im guessing it is something to do with the headlight switch, but I thought I would get your guys thoughts before I went on a wild goose chase. Thanks for any help.
Elder User
Joined: Apr 2002
Posts: 950
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From: West Bend
First thing I'd check is pull one battery + lead off and hook an ammeter multimeter between the 2nd battery + and battery cable to get a measure of how many amps you're drawing with the key off. Then while that's reading your current drain start pulling fuses one by one until you find which one kills the constant drain.
The only thing that should really pull any power with the key off on these trucks that I can think of would be the radio (to keep radio station presets stored in memory)
Got any car chargers etc plugged in the cigarette lighter? Can't remember if the socket is switched power or not. Some vehicles are, some aren't. If you suspect the light switch you could disconnect the plug on the back of it to see if it makes a difference.
The best way to find it though is to monitor with an ammeter so you can find what the drain is w/o having to wait a few days until your batteries are drained.
Ditto on the floor switch. Cheap easy fix though!
The only thing that should really pull any power with the key off on these trucks that I can think of would be the radio (to keep radio station presets stored in memory)
Got any car chargers etc plugged in the cigarette lighter? Can't remember if the socket is switched power or not. Some vehicles are, some aren't. If you suspect the light switch you could disconnect the plug on the back of it to see if it makes a difference.
The best way to find it though is to monitor with an ammeter so you can find what the drain is w/o having to wait a few days until your batteries are drained.
Ditto on the floor switch. Cheap easy fix though!
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Senior User
Joined: Sep 2009
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From: Pittsburg KS
the floor switch hasent worked since we bought the truck last fall....unless it was stuck down or something and it released, I will defiantly check it. No radio and probably nothing plugged into power outlet, But I will check it out too. Thanks for the quick replies, I will hopefully get to check this out soon.
Logistics Pro
Joined: Sep 2007
Posts: 3,737
Likes: 179
From: Western Mass
Definitely check the floor switch. I had an issue with mine where it stopped working while I was switching from high to low, while driving at night 
Turns out the contacts were corroded and everything was full of grit. Being cheap I cleaned it out and it works fine again.
Also check the main headlight switch on the dash. They are notorious for overheating and melting. I fixed that too, can't remember if it was to fix a problem or just something I noticed. Something shorting in there could kill the battery over time.
Turns out the contacts were corroded and everything was full of grit. Being cheap I cleaned it out and it works fine again.
Also check the main headlight switch on the dash. They are notorious for overheating and melting. I fixed that too, can't remember if it was to fix a problem or just something I noticed. Something shorting in there could kill the battery over time.
Posting Guru
Joined: Dec 2009
Posts: 2,322
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From: Dairy, OR
For sure follow swooshcmk's advice on using a meter to chase it down. First thing I replace in any old ford truck I get is the floor switch. I figure anything my muddy size 13's is going to be stomping on best be in great shape and ready for abuse. Besides they are under $10
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Senior User
Joined: Sep 2009
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From: Pittsburg KS
I pulled the floor switch, and like you guys thought the switch was pretty corroded. I just put a basic on/off switch in and the lights work fine now. Im gonna put a toggle switch in on the dash But Im still drawing about 75 mA with the key off. I pulled all the fuses one by one and there was still current drawing off the battery. Ive been using the truck a lot recently, I ran into town a couple times, and have been letting the truck run as much as I can, so the batteries have had plenty of opportunity to charge, but they have been steadily discharging to where I now have to jump the truck to start it. Ive been disconnecting the batteries when Im not using the truck, so Im starting to think the alternator is my problem. I talked to the guy a napa and he told me that sometimes when alternators go bad they can draw power when there not running which I didnt know. So Im gonna take the truck into napa tomorrow for them to test the alternator and batteries.
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Lead Driver
Joined: Dec 2006
Posts: 6,496
Likes: 94
From: So. Jersey
Is the alternator putting out around 14.6 or atleast over battery voltage when it's running?
You may have a faulty voltage regulator or alternator or bad ground to the regulator.
Check battery voltage first, should be 12.6 on a charged battery.
Now start the truck and check voltage at the battery again. Is it up around 14 volt like it should be?
You may have a faulty voltage regulator or alternator or bad ground to the regulator.
Check battery voltage first, should be 12.6 on a charged battery.
Now start the truck and check voltage at the battery again. Is it up around 14 volt like it should be?
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Junior User
Joined: Sep 2010
Posts: 51
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From: Latrobe, PA
Is the alternator putting out around 14.6 or atleast over battery voltage when it's running?
You may have a faulty voltage regulator or alternator or bad ground to the regulator.
Check battery voltage first, should be 12.6 on a charged battery.
Now start the truck and check voltage at the battery again. Is it up around 14 volt like it should be?
You may have a faulty voltage regulator or alternator or bad ground to the regulator.
Check battery voltage first, should be 12.6 on a charged battery.
Now start the truck and check voltage at the battery again. Is it up around 14 volt like it should be?
Thread Starter
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Senior User
Joined: Sep 2009
Posts: 104
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From: Pittsburg KS
I had to run into town today to grab a few things anyway so I charged up the batteries last night and took the truck by napa since they have much better testers than I do. Both batteries were fine, but the alternator was only putting out about 12.5 volts, there gonna have a new one in for me Friday morning and hopefully this will put an end to the electrical problems for awhile. oh also stopped at the ford dealer and picked up 8 new glowpulgs and got a toggle switch to replace the floor switch for the lights so hopefully I can fix all the broken stuff thats been annoying me.
Lead Driver
Joined: Dec 2006
Posts: 6,496
Likes: 94
From: So. Jersey
I had to run into town today to grab a few things anyway so I charged up the batteries last night and took the truck by napa since they have much better testers than I do. Both batteries were fine, but the alternator was only putting out about 12.5 volts, there gonna have a new one in for me Friday morning and hopefully this will put an end to the electrical problems for awhile. oh also stopped at the ford dealer and picked up 8 new glowpulgs and got a toggle switch to replace the floor switch for the lights so hopefully I can fix all the broken stuff thats been annoying me.
Lead Driver
Joined: Dec 2006
Posts: 6,496
Likes: 94
From: So. Jersey
Not a stupid question, if you don't know you don't know. Anyways it's in the engine bay on the passenger (right) side fender well. It's a metal box with a plug in the side of it.
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Senior User
Joined: Sep 2009
Posts: 104
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From: Pittsburg KS
Well Im still stuck, I replaced the alternator and the voltage regulator and just replaced the connector that plugs into the voltage regulator today, but the truck is still not charging. I also ran a wire directly from the metal plate on the VR to the negative battery post to make sure I had a good ground but still not charging. I spliced the new connector in in the same orientation as the old connector. I have 12 volts going into the S terminal from the green wire and nothing come out of the F terminal or A terminal, but I do have between 200 and 300 miliamps coming out of the I terminal, but with the old connector there is no wire coming from the I connector.
Im wondering if I got either a defective voltage regulator or if my wires are mixed up.
Thanks for any help
Im wondering if I got either a defective voltage regulator or if my wires are mixed up.
Thanks for any help
Post Fiend
Joined: Nov 2003
Posts: 21,285
Likes: 15
From: Nutter Fort, WV
Try this.
F terminal regulator to the F terminal alternator
I terminal on the regulator get power from a red/green wire from the key switch (hot when on)
A terminal gets tied into the battery lead from the alternator.
On the 85 trucks, if I remember right there was no S wire on the regulator or alternator.
F terminal regulator to the F terminal alternator
I terminal on the regulator get power from a red/green wire from the key switch (hot when on)
A terminal gets tied into the battery lead from the alternator.
On the 85 trucks, if I remember right there was no S wire on the regulator or alternator.