Brake lights-- electrical question

Reply Subscribe

Thread Tools

Search this Thread

Sep 21, 2011 | 08:04 PM

f100today

Thread Starter

Posting Guru

Joined: Jul 2011

Posts: 1,650

Likes: 16

From: DFW Texas

Brake lights-- electrical question

Ok, First off, I am no electrical guy so bare with me. My tail lights work but my brake lights do not work. I have narrowed it down to this. It is not the switch at the pedal. I have 12v at the switch and leaving the switch. Somewhere between the switch and the plug on the drivers inner fender I am losing something. I get like 4 to 6 volts at that plug. Where does the wire go from the pedal switch? Steering column? relay? I have somewhat tried to chase it through the dash but there is so much dang tape wrapped around these wires

! Any thoughts?

Thanks,
Tim

Sep 21, 2011 | 09:03 PM

catln7

New User

Joined: Aug 2006

Posts: 22

Likes: 0

Power goes from the brake switch then to the turn signal switch.
The turn signal switch does 2 things.
It routes the brake light to the opposite lamp on a turn and connects the flasher unit to the bulbs to be flashed. (Front, rear and in the dash).
Brake and turn signals use the same lamp filament for that side.

Chris

Sep 21, 2011 | 09:53 PM

f100today

Thread Starter

Posting Guru

Joined: Jul 2011

Posts: 1,650

Likes: 16

From: DFW Texas

Well, I just went out and turned my flashers on to discover the rear ones do not work. Fronts only. The turn signals do work and the driving (Night) lights work as well. No brake and no flasher.

Sep 21, 2011 | 11:03 PM

NumberDummy

Ford Parts Specialist

Joined: Nov 2006

Posts: 88,826

Likes: 784

From: Simi Valley, CA

Please, when asking questions, list all the pertinent information.

There are two different types of brake light switches, they look and mount differently to the pedal. The switch used 1969/72 is adjustable.

It may be "hot" but if not properly adjusted, will not be making contact.

There are TWO flashers. The T/S flasher mounts behind the instrument cluster.

The H/D 4 way emergency flasher nestles into a bracket. One screw attaches the bracket to the dash adjacent to the radio.

Sep 22, 2011 | 05:03 AM

f100today

Thread Starter

Posting Guru

Joined: Jul 2011

Posts: 1,650

Likes: 16

From: DFW Texas

Ok, this is a 72 model. I checked the switch and bypassed it as well. No problem at the switch. Adjusted correctly as well. The flashers I did not know about. I have had this truck all of three days; I am not familiar with these trucks and their electrical systems. The pertinent info is not all that obvious to me. Sorry

So my next question is, could a bad flasher cause the brakes lights not to come on?

Sep 22, 2011 | 05:47 AM

jowilker

Fleet Owner

Joined: Jun 1999

Posts: 24,552

Likes: 74

From: Creedmoor, North Carolina

Tim, If you have only had the truck for 3 days, maybe we can cut you a little slack.

There are 4 wires going to the rear of the truck. 1 is for the tail lights, 1 is for the backup, the other 2 flasher & brake (shared). There is a factory plug near the end of the drivers side frame rail. You can unplug it, and test it with a circuit tester. Brake lights share with flashers, tails & backups use 1 each. The easiest thing to do is see if you can find 2 wires that will impulse flash the circuit tester light at that juncture.

If yes you move rearward, if no you move towards the front. You should be able to see the wires along the rail, inspecting it for damage.

There can be issues with the brake/signal at the steering column, but I like to start at the rear first, others may like to start at the front.

There are 2 flashers on the truck, 4 way & turn, yes they share the same 2 wires going to the rear. Try them first, if all corners are blinking the wiring is good and the turn signal switch is likely the culprit.

That should give you something to chew on.

John :_X06