1979 Ford F-150 4x4 Brakelight problems!

GotMuddy2 · 11-20-2006, 09:33 PM

Hopefully someone can put me in the right direction!

The problem is that my brake lights and hazards aren't working at all. I am at wits end. I have replaced the bulbs, all fuses, and tested the circuit front to back and back to front. The hazard relay is good. I get 12v at the brake switch and at the flasher relay with the brake pedal unengaged. When engaged I get 12v through the brake switch. But at the taillight I get nothing. When I pull the flasher button on the column I get a chassis ground everywhere in the brakelight/hazard circuit and no clicking in the relay. I don't know where to go from here. I am an electronics technician currently serving our great Country in the U.S. Coast Guard in Portsmouth ,VA , so dont be afraid to get to technical. I have a repair manual and have owned this truck for more than 7 years so, I'm not afraid to get down and dirty to repair it. The manual has a wiring diagram in it but it is very Vague and doesn' really give any info as far as resistance and voltage in different states of the circuit. PLEASE, any help would be greatly appreciated. Thanks in advance!!!!

mrjohnwayne · 11-21-2006, 07:17 AM

it seems that you have a cut wire. I would start from the front and work my way back to the lights tracing the wires.

75K30 · 11-21-2006, 04:19 PM

mrjohnwayne is right on track, it does sound like an open wire. The big question is which one? It is very common for these year trucks, to lose the directional switch in the column. The very first step would be to verify that the 20A. fuse labeled haz/stop is good, (fuse block) and 12V is present at the black and yellow side. Then check the red / wht side after a good fuse is installed. This red / wht goes to the stop light switch located on the pedal. BTW, your wiring diagram is accurate enough for this type of troubleshooting. This is a simple 12VDC circuit. You will not see resistance greater than a couple of OHMS, and the voltage will always be at around 12VDC (depending on battery condition). If you were to see less than that, the lights would still work, just at a brighter, or dimmer glow. Anyway, back to the problem, once you are sure that the red / wht wire has voltage, and you are sure that the switch is good, verify voltage at the red / black wire from the stop light switch to the directional switch. I suspect that the problem is here. I am assuming that both stoplights are out so this would eliminate the wires that feed them individually. The problem sounds like the source that feeds this circuit, and everything can be found in the cab. Good luck.

GotMuddy2 · 12-01-2006, 12:13 PM

Thanks very much guys, I tested through the directional switch and found it to be the problem. So now the truck sits and it will till after Christmas when, I can justify buying a $92 switch. Again , thanks for the help.

75K30 · 12-01-2006, 01:08 PM

I might have one layin around if you are interested. I actually have a whole column. Does yours have cruise, and is it a tilt? Mine is not, and it does not have cruise. That is important, because, the switch is different. Let me know.

11-20-2006, 09:33 PM	#1
GotMuddy2 Junior Member Join Date: Nov 2006 Location: Portsmouth, Va Posts: 4	1979 Ford F-150 4x4 Brakelight problems! Hopefully someone can put me in the right direction! The problem is that my brake lights and hazards aren't working at all. I am at wits end. I have replaced the bulbs, all fuses, and tested the circuit front to back and back to front. The hazard relay is good. I get 12v at the brake switch and at the flasher relay with the brake pedal unengaged. When engaged I get 12v through the brake switch. But at the taillight I get nothing. When I pull the flasher button on the column I get a chassis ground everywhere in the brakelight/hazard circuit and no clicking in the relay. I don't know where to go from here. I am an electronics technician currently serving our great Country in the U.S. Coast Guard in Portsmouth ,VA , so dont be afraid to get to technical. I have a repair manual and have owned this truck for more than 7 years so, I'm not afraid to get down and dirty to repair it. The manual has a wiring diagram in it but it is very Vague and doesn' really give any info as far as resistance and voltage in different states of the circuit. PLEASE, any help would be greatly appreciated. Thanks in advance!!!! __________________ 2005 Ford Excursion 6.0 PSD 1979 Ford F-150 4x4 1973 Harley Davidson FLH

11-21-2006, 07:17 AM	#2
mrjohnwayne Senior Moderator Join Date: Apr 2005 Location: Texas Posts: 3,896	it seems that you have a cut wire. I would start from the front and work my way back to the lights tracing the wires. __________________ John Wayne 2000 F-350 7.3L Powerstroke 4x4

12-01-2006, 12:13 PM	#4
GotMuddy2 Junior Member Join Date: Nov 2006 Location: Portsmouth, Va Posts: 4	Thanks very much guys, I tested through the directional switch and found it to be the problem. So now the truck sits and it will till after Christmas when, I can justify buying a $92 switch. Again , thanks for the help. __________________ 2005 Ford Excursion 6.0 PSD 1979 Ford F-150 4x4 1973 Harley Davidson FLH

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11-21-2006, 04:19 PM	#3
75K30 Senior Member Join Date: Jul 2006 Posts: 3,690	mrjohnwayne is right on track, it does sound like an open wire. The big question is which one? It is very common for these year trucks, to lose the directional switch in the column. The very first step would be to verify that the 20A. fuse labeled haz/stop is good, (fuse block) and 12V is present at the black and yellow side. Then check the red / wht side after a good fuse is installed. This red / wht goes to the stop light switch located on the pedal. BTW, your wiring diagram is accurate enough for this type of troubleshooting. This is a simple 12VDC circuit. You will not see resistance greater than a couple of OHMS, and the voltage will always be at around 12VDC (depending on battery condition). If you were to see less than that, the lights would still work, just at a brighter, or dimmer glow. Anyway, back to the problem, once you are sure that the red / wht wire has voltage, and you are sure that the switch is good, verify voltage at the red / black wire from the stop light switch to the directional switch. I suspect that the problem is here. I am assuming that both stoplights are out so this would eliminate the wires that feed them individually. The problem sounds like the source that feeds this circuit, and everything can be found in the cab. Good luck.

12-01-2006, 01:08 PM	#5
75K30 Senior Member Join Date: Jul 2006 Posts: 3,690	I might have one layin around if you are interested. I actually have a whole column. Does yours have cruise, and is it a tilt? Mine is not, and it does not have cruise. That is important, because, the switch is different. Let me know.