Mystery Short
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Mystery Short
I have 1990- F150--300--5spd.
When placing a light between the negative terminal and negative cable it lights.
I have gone thru all the steps in my Haynes Manual ---pulling fuses,etc. and the light does not go out.
My alternator is definitely charging. When I removed the upper wiring harness(regulator) the light stayed on. I tried to remove the harness to the bottom wiring harness(rectifier) I couldn't remove it.
Is there a trick to get it out? Does it need to removed to check out the alternator? Or is the upper wiring harness removal sufficient?
Anyway, I stumped!
Anyone have any idea what I should to next?
When placing a light between the negative terminal and negative cable it lights.
I have gone thru all the steps in my Haynes Manual ---pulling fuses,etc. and the light does not go out.
My alternator is definitely charging. When I removed the upper wiring harness(regulator) the light stayed on. I tried to remove the harness to the bottom wiring harness(rectifier) I couldn't remove it.
Is there a trick to get it out? Does it need to removed to check out the alternator? Or is the upper wiring harness removal sufficient?
Anyway, I stumped!
Anyone have any idea what I should to next?
Last edited by Citation 2; Sep 30, 2005 at 12:31 PM.
Tuned
Joined: Feb 2003
Posts: 495
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From: Cincinnati, Ohio
Doubt that your problem is with the alternator since it is working OK. Sounds like your short is in a circuit that is not fused, possibly in a fusible link circuit that isn't drawing enough to melt the link. I would disconnect all positive circuits after the battery, starter relay, fusible links, etc., and start there. This should at least get you to the branch circuit that is at fault and then using a circuit diagram you can troubleshoot each component until you find the culprit. Very slow process but it works.
Also, did you pull all of the fuses under the dash as well as the fuse block under the hood if you have one.
John
Also, did you pull all of the fuses under the dash as well as the fuse block under the hood if you have one.
John
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I did a search on my problem and few months back, someone had the same fault show up on their truck.
Someone in the responses mentioned closing the doors and making sure the hood light was disconnected, when going thru the process of fuse pulling.
Well, removed the hood light bulb and closed the doors---got the negative battery terminal off---getting set to go thru the process of again pulling the fuses. But, the short had disappeard.
I tried to find the wiring diagram for the hood light. But, no luck.
Does anyone know if the wire for the hood light goes thru the fuse pannel inside the truck or does it go to a constant hot lead?
If, the wire doesn't go thru the fuse pannel, I have solved my problem and the light was the cause of my mystery short.
The small wires at the bottom of the bulb were not factory fresh and I could see where it might have resulted in causing me grief.
Someone in the responses mentioned closing the doors and making sure the hood light was disconnected, when going thru the process of fuse pulling.
Well, removed the hood light bulb and closed the doors---got the negative battery terminal off---getting set to go thru the process of again pulling the fuses. But, the short had disappeard.
I tried to find the wiring diagram for the hood light. But, no luck.
Does anyone know if the wire for the hood light goes thru the fuse pannel inside the truck or does it go to a constant hot lead?
If, the wire doesn't go thru the fuse pannel, I have solved my problem and the light was the cause of my mystery short.
The small wires at the bottom of the bulb were not factory fresh and I could see where it might have resulted in causing me grief.
Posting Guru
Joined: Nov 2004
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From: Asheville, NC
Just to clarify, you dont have a short. If you had a short, you'd be blowing fuses.
You have a voltage drain. They are often a pain to find. Ask me. I had to deal with an '83 that had been rewired by an idiot... No, not me! Its now in good shape and can sit for a week without discharging the battery. I'm happy.
Best of luck!
You have a voltage drain. They are often a pain to find. Ask me. I had to deal with an '83 that had been rewired by an idiot... No, not me! Its now in good shape and can sit for a week without discharging the battery. I'm happy.
Best of luck!
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Holmesurer01.
I didn't fool around with it today. Other things to do.
What process did you go thru to find your fault? Any helpfull hints?
I still feel something is not right. An electrical surge shows itself every once in awhile. My gauge in truck will jump to discharge and then correct itself back to normal.
Thanks,
Ray
I didn't fool around with it today. Other things to do.
What process did you go thru to find your fault? Any helpfull hints?
I still feel something is not right. An electrical surge shows itself every once in awhile. My gauge in truck will jump to discharge and then correct itself back to normal.
Thanks,
Ray
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From: Virginia
My gauge in truck will jump to discharge and then correct itself back to normal.
Where the battery + hooks to the large post of the starter relay, you should have some smaller wires there. The smaller wires power the whole truck. You may have one wire that splits up into several, or have several on the large post. One of them will be the alternator output wire.
What you can do is take wires off out there. That way you can seperate the problem quickly as to whether it's the alternator or a problem inside the truck. If you have the problem again, take the one of these large wires off that go to the alternator, or if it's easier, take the large wire off the back of the alt.
Your problem is intermittent. So it may take awhile and a couple of guesses till you find it.
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Franklin2,
You were right--the alternator.
Took the truck out this morning, ran great for awhile and then absolutely no gas peddle, sputtering and died.
Thought, tow truck here I come. Called Vicky and she brought a spare battery to the truck. Ran for awhile. Dead again. Jumped the truck and let the truck battery be charged from her car for a few minutes and off again. Had to do this twice to go 2 miles.
Got it home not needing a tow.
Let the truck sit for about 30 minutes, went out and it fired right up. Checked the voltage from the alternator at the battery and my meter was showing the right numbers for a good alternator. However, I continued to let it idle and constantly checked the voltage and it was dropping more and more, the longer the engine was running.
Took the alternator off and had it tested. Verdict, bad alternator.
Got a new one. Truck runs great, again and all those little quirks I was trying to eliminate are now gone.
Thanks Guys.
Ray
You were right--the alternator.
Took the truck out this morning, ran great for awhile and then absolutely no gas peddle, sputtering and died.
Thought, tow truck here I come. Called Vicky and she brought a spare battery to the truck. Ran for awhile. Dead again. Jumped the truck and let the truck battery be charged from her car for a few minutes and off again. Had to do this twice to go 2 miles.
Got it home not needing a tow.
Let the truck sit for about 30 minutes, went out and it fired right up. Checked the voltage from the alternator at the battery and my meter was showing the right numbers for a good alternator. However, I continued to let it idle and constantly checked the voltage and it was dropping more and more, the longer the engine was running.
Took the alternator off and had it tested. Verdict, bad alternator.
Got a new one. Truck runs great, again and all those little quirks I was trying to eliminate are now gone.
Thanks Guys.
Ray
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From: Virginia
Originally Posted by baddraw
Just a tip for the future with truck running remove a battery cable careful not to ground it and if alt is working properly truck should continue to run if it doesn't chances are alt is bad.
I have personally burnt up an ignition module doing this very thing.
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