no brake lights -2001 F150
#1
no brake lights -2001 F150
A friend has a 2001 F150 which has developed a troublesome problem. When you turn on the parking/headlamps, the brake lights (including the CHMSL) come on and remain on bright. If you hit the turn signal or 4 ways, the indicator(s) in the cluster light steadily and the front corner lamps go to full brightness with no blinking...
We checked all fuses, they are all fine. Any ideas what could cause this and/or possible remedies?
We checked all fuses, they are all fine. Any ideas what could cause this and/or possible remedies?
#2
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Lets start with some specs on the truck.
1. Trim level & body style ( the wiring diagrams are a bit different for specific trim levels and body styles ), and if he has the factory trailer tow package, with all the relays installed.
2. If the main headlamp switch is in the off position :
2.1. Do the turn signals work correctly front and rear ?
2.2. Do the 3 brake lights ( without the turn signals on ) work correctly ?
2.3. Do the 3 brake lights ( with the turn signals on ) work correctly ?
3. With the problem noted, do the trailer tow wires exhibit the same symptoms as the truck ( both L and R S/T/x and the parking lamps.
4. What happend when you turn the main headlamp switch to on, and press on the brake lamps ( no change, or something different, note both front and rear ).
Those are the start to the questions that I can see.
1. Trim level & body style ( the wiring diagrams are a bit different for specific trim levels and body styles ), and if he has the factory trailer tow package, with all the relays installed.
2. If the main headlamp switch is in the off position :
2.1. Do the turn signals work correctly front and rear ?
2.2. Do the 3 brake lights ( without the turn signals on ) work correctly ?
2.3. Do the 3 brake lights ( with the turn signals on ) work correctly ?
3. With the problem noted, do the trailer tow wires exhibit the same symptoms as the truck ( both L and R S/T/x and the parking lamps.
4. What happend when you turn the main headlamp switch to on, and press on the brake lamps ( no change, or something different, note both front and rear ).
Those are the start to the questions that I can see.
#4
Originally Posted by SSCULLY
Lets start with some specs on the truck.
1. XL Regular cab longbed, 4x2, 4.2 L auto. The truck had the flat 4 plug from the factory, but no receiver, so I'm guessing it doesn't have the tow package.
2.1. They work until the brake pedal is pressed, at which
time they just stay stuck on.
2.2. Not really, since they are on the whole time.
2.3. They are just on all the time if the light switch is on.
3. Have not checked, but will.
4. Brake lights are constantly lit when park/headlamp switch is on, although, if you press the pedal, there is a very slight increase in brightness.
Does "MFS" stand for "multi-function switch?"
Last edited by IKE; 12-17-2006 at 10:39 AM.
#5
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Originally Posted by IKE
...<snip>...Does "MFS" stand for "multi-function switch?"
If you want to short cut to testing the MFS, it can't hurt, and would be in the list of items, depending on the answers to the questions above.
If you want to go right to testing, remove the MFS from the steering wheel column. here is the procedure :
#6
I received a reply and added the answers above to keep them all in one place.
I did think of something else, there was an issue with the trailer wiring under the bed a while back necessitating a repair, could something screwed up back there cause symptoms such as this? Is there a way to isolate that harness?
I did think of something else, there was an issue with the trailer wiring under the bed a while back necessitating a repair, could something screwed up back there cause symptoms such as this? Is there a way to isolate that harness?
Last edited by IKE; 12-18-2006 at 04:18 PM.
#7
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Well that is some good detail.
Not withstanding Steve's recomendation to test the MFS, I woudl take a slightly different approach.
Remove both rear bulbs, and see if the CHMSL still has the same problem, and check if with the parking lamps on, that the fronts are on the low element, and if you use the turn signals, or 4 Way, that th efront flash ( albeit quickly due to limited load ).
With the slightly brighter, I am guessing at a bad ground on the rear of the truck, and the stop lamp is where it is deriving ground from ( via the CHMSL or BOO switch ).
Removing both the rear bulbs will stop any ground finding.
Question on the flat 4 under the rear bumper, is this part of the factory system, or an add on kit, or DIY add on ?
Trying to figure out if it is using the trailer tow circuits in the truck, or the actual truck lights ( should not be ).
Not withstanding Steve's recomendation to test the MFS, I woudl take a slightly different approach.
Remove both rear bulbs, and see if the CHMSL still has the same problem, and check if with the parking lamps on, that the fronts are on the low element, and if you use the turn signals, or 4 Way, that th efront flash ( albeit quickly due to limited load ).
With the slightly brighter, I am guessing at a bad ground on the rear of the truck, and the stop lamp is where it is deriving ground from ( via the CHMSL or BOO switch ).
Removing both the rear bulbs will stop any ground finding.
Question on the flat 4 under the rear bumper, is this part of the factory system, or an add on kit, or DIY add on ?
Trying to figure out if it is using the trailer tow circuits in the truck, or the actual truck lights ( should not be ).
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#8
Originally Posted by SSCULLY
Question on the flat 4 under the rear bumper, is this part of the factory system, or an add on kit, or DIY add on ?
Trying to figure out if it is using the trailer tow circuits in the truck, or the actual truck lights ( should not be ).
Trying to figure out if it is using the trailer tow circuits in the truck, or the actual truck lights ( should not be ).
I'll pass on the results of the bulb removal and see where that takes us.
Thanks!
Last edited by IKE; 12-18-2006 at 04:12 PM.
#9
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Originally Posted by IKE
It is the factory wiring, but a new plug was spliced on during a repair...
I'll pass on the results of the bulb removal and see where that takes us.
Thanks!
I'll pass on the results of the bulb removal and see where that takes us.
Thanks!
#10
Well, that very well could be the issue, there was a ground problem with the 4 pin (which is all the truck has, no 7 pin connector) and a new plug was spliced in with a new ground. Is the lead to the 4 pin a seperate harness, ie, is there a point where that can be unplugged to isolate it? (I don't recall and the truck isn't here to look at)
#11
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Originally Posted by IKE
Well, that very well could be the issue, there was a ground problem with the 4 pin (which is all the truck has, no 7 pin connector) and a new plug was spliced in with a new ground. Is the lead to the 4 pin a seperate harness, ie, is there a point where that can be unplugged to isolate it? (I don't recall and the truck isn't here to look at)
On my '01 and my '06 it was easier to see by dropping the spare tire.
Take a bulb out of one of the S/T/T and check the ground to the frame ( clean bolt ) as a starting point. Should be 0 ohms or the continuity tone.
#12
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Originally Posted by IKE
SSCULLY: Thanks for the help, we traced the problem to the plug. For now it has been clipped off and will be replaced at a later date. All lights now work properly.
Thanks again!
Thanks again!
Thank yourselves for problem diagnoses 101, completed sucessfully !