Odd Electrical Issue
Thread Starter
|
New User
Joined: Apr 2007
Posts: 23
Likes: 0
Odd Electrical Issue
Help me please........
I have been trying to chase down a short of some sort in my 1985 F-150. It is in the brake light circuit. It is VERY intermittent. I can go for three days with no issue and then all of a sudden the fuse blows. Heres what happens:
When I press the break pedal down the lights activate. Everything appears ok - then the fuse blows and no more brake lights. I have traced the wiring under the truck to the rear, looked at all the connections, checked inside the tail lights for water or shorts, looked for bad connections, checked under the hood for any possible bad connectors or connections, and re-did ANY splice connections in the truck.
For the life of me, I cannot seem to find this short. Any reccomendations or help anyone can offer would be really appreciated. I am at my wits end and just about ready to jump the fuse with a piece of wire to see what happens.
Thanks soo much!!
-John
I have been trying to chase down a short of some sort in my 1985 F-150. It is in the brake light circuit. It is VERY intermittent. I can go for three days with no issue and then all of a sudden the fuse blows. Heres what happens:
When I press the break pedal down the lights activate. Everything appears ok - then the fuse blows and no more brake lights. I have traced the wiring under the truck to the rear, looked at all the connections, checked inside the tail lights for water or shorts, looked for bad connections, checked under the hood for any possible bad connectors or connections, and re-did ANY splice connections in the truck.
For the life of me, I cannot seem to find this short. Any reccomendations or help anyone can offer would be really appreciated. I am at my wits end and just about ready to jump the fuse with a piece of wire to see what happens.
Thanks soo much!!
-John
Senior User
Joined: Aug 2006
Posts: 113
Likes: 2
From: Texas
Scrap the jumper wire idea, you might cause yourself more heartaches. I would first check the fuse box to be sure the right fuse was in it, then check the bulbs to be sure they are the right ones. If all this is in order, you could have a hot wire rubbing against the frame and grounding itself. This involves tracing the wiring from the tail lights to the brake switch on the pedel. I had this problem once on an older pickup and found the short just ahead of the tail lights. I was lucky. Good luck.
Posting Guru
Joined: Jun 2004
Posts: 1,635
Likes: 0
From: Niceville, FL.
Are there any added accessories powered from the same fuse (Fuse #1, 20 A.) as the Brake Lights that could be overloading the circuit? Items such as electric trailer brake controller, CD player or CB Radio could be using most of the available current and when you apply the brakes, the added current of the brake lamps causes the fuse capacity to be exceeded.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,806
Likes: 246
From: Piney Woods of East Texas
Intermitten shorts can be hard to locate. It may show up as a high resistance. To test for this you need to disconnect the neg side of the battery to do some testing with DVM.
Remove the bulbs and verify they are the correct ones. You will need a wiring diagram to locate the connectors, and color codes for the wires and all devices that are in the circuit. You can get the brake lights color from the tale light sockets.
See if you can measure any resistance between ground and the brake lights contacts in the socket. If so you need to starting working backwards. Disconnect the main connection that connects the tale lights to the main harness. Test at the main harness connection, should have 1 wire for each brake light/side. Here you may be able to isolate which side its on. If still present I would look at the wires running to the brake switch. Then the turn signal switch. Will need to disconnect the turn signal connector and test the connections to the brake lights. If the high resistance has gone a way, it will be in the column.
Good luck these can be very hard to locate.
Remove the bulbs and verify they are the correct ones. You will need a wiring diagram to locate the connectors, and color codes for the wires and all devices that are in the circuit. You can get the brake lights color from the tale light sockets.
See if you can measure any resistance between ground and the brake lights contacts in the socket. If so you need to starting working backwards. Disconnect the main connection that connects the tale lights to the main harness. Test at the main harness connection, should have 1 wire for each brake light/side. Here you may be able to isolate which side its on. If still present I would look at the wires running to the brake switch. Then the turn signal switch. Will need to disconnect the turn signal connector and test the connections to the brake lights. If the high resistance has gone a way, it will be in the column.
Good luck these can be very hard to locate.
Thread Starter
|
New User
Joined: Apr 2007
Posts: 23
Likes: 0
thanks for all the help. I guess the one part I did not look at yet is the switch in the brake pedal that makes contact activate the brake lights. I traced out all the wiring, and recently (while replacing the rear gas tank) was able to inspect the wires that run from the front to the back. Harnesses all looked good to at this time. I re-electrical taped all the connections (i do have a hitch harness) and made sure the barrel clamps are all tight and water free.
As far as I know the only things on this circuit are the brake lights and the 4-way flashers. I hooked a CB and 3-outlet strip to the cigarette lighter recently, but no problems there because that all works fine.
I bought this truck from someone who apparently liked to jimmy-rig things, so I have been searching for anything done poorly. There have been several times I stumbled onto a connection that was done by twisting two wires together and taping over it. Poor truck didn't deserve to be treated that way. haha.
Thanks again and any other help is much appreciated.
As far as I know the only things on this circuit are the brake lights and the 4-way flashers. I hooked a CB and 3-outlet strip to the cigarette lighter recently, but no problems there because that all works fine.
I bought this truck from someone who apparently liked to jimmy-rig things, so I have been searching for anything done poorly. There have been several times I stumbled onto a connection that was done by twisting two wires together and taping over it. Poor truck didn't deserve to be treated that way. haha.
Thanks again and any other help is much appreciated.
Fleet Mechanic
Joined: Aug 2007
Posts: 1,806
Likes: 246
From: Piney Woods of East Texas
Check to see if he had electric brakes at one time. My dad made a connection under the dash for his and caused me problems. Lights would not work, but did not blow any fuses.
Posting Guru
Joined: Jun 2004
Posts: 1,635
Likes: 0
From: Niceville, FL.
If you have cruise control the brake light circuit also sends voltage to the cruise solid state module to tell it to disengage. Long shot but I'd disconnect the connectors at the module to eliminate it as a source of the problem. Also, the stop light circuit goes through the steering column and turn signal switch so problem could be there.
Trending Topics
Moderator
Joined: Jan 2001
Posts: 56,971
Likes: 2,731
From: Virginia
Remember the brake circuit leaves the brake switch under the dash, and goes up into the steering column. So I would look at the wiring under the dash, and inspect it inside the steering column, by taking the cover off near the cluster and look as good as you can from there.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
AEV FXL Super Duty - the Super Duty Raptor Ford Doesn't Make
Brett Foote
Lobo Vs Lobo: Proof the F-150 Lobo Should Be Even Lower!
Michael S. Palmer
Ford's 2001 Explorer Sportsman Concept Looks For a New Home
Verdad Gallardo
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Thread Starter
|
New User
Joined: Apr 2007
Posts: 23
Likes: 0
ok - don't laugh a me here because I am an admitted novice learning as i go. (that's why I got the truck I did because they are easier to learn on)
I took almost all that dash apart, but I could not seen to get the headlight switch off, so I was limited by that. I could not see anything while poking around with a flashlight other than a problem that might be in the same circuit as the brakes.
The "EMISSIONS" light (which is all the way to the left on my truck) was smashed and desintigrated. The wires, which would have been inside the light bulb, were touching each other. That would cause a short when the emissions light was called to light up.
Is there any chance that this emissions light would be on the same circuit as the brakes/4-ways? I am looking through some of the wiring diagrams I have, but I am not sure.
Thoughts??
Thanks AGAIN for all the help!!
I took almost all that dash apart, but I could not seen to get the headlight switch off, so I was limited by that. I could not see anything while poking around with a flashlight other than a problem that might be in the same circuit as the brakes.
The "EMISSIONS" light (which is all the way to the left on my truck) was smashed and desintigrated. The wires, which would have been inside the light bulb, were touching each other. That would cause a short when the emissions light was called to light up.
Is there any chance that this emissions light would be on the same circuit as the brakes/4-ways? I am looking through some of the wiring diagrams I have, but I am not sure.
Thoughts??
Thanks AGAIN for all the help!!
Fleet Mechanic
Joined: Aug 2007
Posts: 1,806
Likes: 246
From: Piney Woods of East Texas
jkrums,
This indicates that there was an prouble with emissons an the prevoius owner did not want the light on. Some eec report a problem it the light as failed. I would repair the light, and connect a diagnostic light and chekc for trouble codes.
The "EMISSIONS" light (which is all the way to the left on my truck) was smashed and desintigrated. The wires, which would have been inside the light bulb, were touching each other. That would cause a short when the emissions light was called to light up.
Thread Starter
|
New User
Joined: Apr 2007
Posts: 23
Likes: 0
After buying the truck I quickly found that the previous owner did a lot with the exhaust system that was a shame. He welded a jimmy-rig in the exhaust manifold and I ended up replacing that manifold with a fully functional junk yard version. Ironic, the part cost me $12 and about 2 hours in a "you pull it" yard. His "fix" probably took longer, and still wouldn't pass emissions. I have a flowmaster muffler that is presently mounted under the cab (literally) - that is next on the list of things to be fixed.
New User
Joined: Aug 2007
Posts: 5
Likes: 0
Just a quick thought from another new guy here...I work for a local telephone company, and vinyl (electrical) tape is evil. It will hold moisture more often than not, and that will create an "open," meaning no lights, when the conductor corrodes. Treat yourself to some nice cold solder (crimp) connectors, and and a wee bit of dielectric grease to keep the insidious water out. A little shrinkwrap applied over that will make your connection as safe as it can be. We use cold connectors instead of a hot solder type, since the connection is more "pure," meaning the current is carried strictly on the copper rather than partly on copper and partly on the metals in your solder.
I haven't played around enough with my 82 F250 yet (just got it about a month ago) to be much help to you with your short issue, but if you clean up the PO's Twist-n-Tape splicing method I think you'll save yourself some aggravation down the road.
I haven't played around enough with my 82 F250 yet (just got it about a month ago) to be much help to you with your short issue, but if you clean up the PO's Twist-n-Tape splicing method I think you'll save yourself some aggravation down the road.
Thread Starter
|
New User
Joined: Apr 2007
Posts: 23
Likes: 0
Thanks for the thoughts. I replaced everything that was spliced with crimp style barrell crimps. I did use some electrical tape over that, but I can remove that and replace it. I also tried this new stuff that the store had. Its paint on type electrical tape. It comes in a container with an applicator that you just dip in the can of "goo" and completely coat whatever you want to protect. I used this on most of the connections for the hitch wiring and away from the engine. I did not use it in the engine compartment because I was unsure how it behaves near heat. I am still looking for the short, so we will see if this helps. See, the short is so intermittent that it could be weeks before I may be able to declare victory. I will definatly keep your comments in mind and thanks for the pointers.
Senior User
Joined: Aug 2005
Posts: 110
Likes: 0
From: Sacramento, CA
Instead of just popping fuses just get a circuit breaker to replace the fuse. and hey if the problem is very intermittent then the breaker may be a temporary solution. ive started to use circuit breakers instead, especially on aux circuits that ive created where i usually blow fuses.