Electrical Nightmare '72 F100
#1
Electrical Nightmare '72 F100
One of the previous owners had spliced into the 13A409 rear harness sometime during the life of the truck. I removed all the splices then reconnected all the wiring (I'm pretty sure it's right), but no brakes lights or 4 way flashers. All others lighting is working including the front 4 ways.
Also, the turn signals front and rear are working.
Any insight would be greatly appreciated!
Also, the turn signals front and rear are working.
Any insight would be greatly appreciated!
#2
#3
#4
#5
Join Date: Mar 2010
Location: San Francisco East Bay
Posts: 1,028
Likes: 0
Received 4 Likes
on
4 Posts
One of the previous owners had spliced into the 13A409 rear harness sometime during the life of the truck. I removed all the splices then reconnected all the wiring (I'm pretty sure it's right), but no brakes lights or 4 way flashers. All others lighting is working including the front 4 ways.
Also, the turn signals front and rear are working.
Any insight would be greatly appreciated!
Also, the turn signals front and rear are working.
Any insight would be greatly appreciated!
If your brake lights don't work but your turn signals do, then half the power is not getting to the bulbs.
If the grounds were bad for any bulb position (right or left), you wouldn't get anything there - no brake light and no turn signal. The ground has to be valid for the turn signals to work, so if you've got turn signals, then it's not the grounds.
If you have an assistant, have them push the brake pedal while you chase power at the splice. If you do not have an assistant, disconnect the brake switch and short the connector (not the switch), in order to fake a "Brakes On" condition. This should apply 12VDC to the wire(s) you're looking for. Make sure to remove the short and re-attach the connector when you're done.
With the "Brakes On", use a voltage tester to find out which wire is (or wires are) supposed to be feeding power back to your bulbs.
I can't quite tell from the schematic which wire is supposed to feed the "Brakes On" signal and which is supposed to feed the "Turn" signal from the flasher. It shouldn't be too hard to figure out which is which, once you find the wire with the "Brakes On" signal.
If you cannot find the "Brakes On" signal anywhere at the splice, the problem is farther forward in the truck.
If the front lights are flashing when you put on the emergency flasher, then it's not the flasher that's bad.
#6
#7
Assistant (good wife), held brake pedal while I used the test light. No power coming from main harness. There is power to the other rear lights, but no brake lights. Looks like I'll be heading up to the next connector in the 14405 harness. Something up front evidently didn't like me messing around with that rats nest in the back!
Trending Topics
#8
Point taken Tedster, but I changed to electronic ignition during the summer. Also, I'm using ACC position during testing.
Done for the night and will get a fresh start in the morning. It's nice to be retired!
#10
Just heading for the garage and saw your post. Before I get testing the brake light switch at the pedal, I need to ask another question. In the wiring diagram I just looked at, the Emergency Flasher switch also gets a signal from the brake light switch. Before I did the work on the rats nest in the back, I installed a new Emergency Flasher switch from Dennis Carpenter's. I thought I'd unplug it and test again, but didn't get past the computer. I'm old, but love the emoji's that apply!
#11
#12
If you have power going through the brake light switch, it should then go through the turn signal switch. Jump out the brake light switch connector like mentioned, then start pin probing the turn signal wires under the column to see if brake light power is going into and coming out of the turn signal switch. One power wire going in, and 2 coming out, same 2 wires as the turn signal uses It's a very common problem for this symptom.
#13
Did any of this stuff work before you fixed the patchwork?
I'm thinking it might be your hazard switch. If turn signals function, then the wiring is correct.
The hazard switch controls the rear brake/turn signals and if that switch is not wired correctly or broken you will not have brake lights. I know you mention you tested it, but if the wiring is broken going to the switch the lights will not work.
I'm thinking it might be your hazard switch. If turn signals function, then the wiring is correct.
The hazard switch controls the rear brake/turn signals and if that switch is not wired correctly or broken you will not have brake lights. I know you mention you tested it, but if the wiring is broken going to the switch the lights will not work.
#14
Did any of this stuff work before you fixed the patchwork?
I'm thinking it might be your hazard switch. If turn signals function, then the wiring is correct.
The hazard switch controls the rear brake/turn signals and if that switch is not wired correctly or broken you will not have brake lights. I know you mention you tested it, but if the wiring is broken going to the switch the lights will not work.
I'm thinking it might be your hazard switch. If turn signals function, then the wiring is correct.
The hazard switch controls the rear brake/turn signals and if that switch is not wired correctly or broken you will not have brake lights. I know you mention you tested it, but if the wiring is broken going to the switch the lights will not work.
Freightrain, I'm getting to believe you are right. I have tested everything but, the brand new out of the box (Made in China) Emergency Flasher switch. I'll pull that out this evening and bench test it.
All of the other lights work, with the exception of the brake lights and rear Emergency Flashers.
I installed a new turn signal switch a few months ago and it has worked fine along with everything else until I redid the rear (13A409) harness and installed the new Emer. Flasher switch.
Is that a "B" model in your avatar?
#15
Surprised no one has mentioned this yet. Check the flashers, there are two. My PO did the exact same thing to run an LED strip, once I cleaned up his mess I had no turn signals. Put the correct flasher in and it was all good .... well almost the PO also chopped up the left front turn signal housing and installed a late model turn signal housing which cased a "slow" turn flash.