brake lights

[CHRIS UNGER]

I am getting my light working on my truckbut having problems getting power to brake light bulbs. Does the wiring have to be ran through the turn signal switch for them to work ? I am missing somethig but i can't put my finger on it. I have headlights and taillights but cannot get power to the "big" bulb.

[randygar]

Yes, the turn signal box under the hood distributes power from the brake lamp switch (hydraulic, on the big T fitting) input to both rear bulbs. Check that the connections to it are good, that it gets the brake lamp input, and if it's not sending it out the back, assume it needs some repair... also verify the 3-lever switch is actually supplying power to the brake lamp system.

--Randy

[brute4c]

First we need to know which turn signal setup you have..there is an early and late style...the late style is simpler and solid state...the early style has a large box with mechanical relays under the hood. I changed my truck from the early style to the late style and documented it here:

http://www.m715zone.com/vb/view.php?...signal_convert

By looking at the first few pics, you can determine if you hae the early or late style setup.

With the early style, the power does route through the distribution box. The later style does not need to.

Most likely, the brake pressure switch is bad.
Follow the brake line from the master cylinder down to the frame rail to a block that has several brake lines and an electrical device screwed into the side. This is the brake light pressure switch.

One of the wires should have battery voltage when the 3 lever light switch's top lever is moved to the right 1 or 2 places from the center, straight up position. Take the plug off the switch and use a test light or meter to verify.

If you dont have power at either in this case, the problem may be in the 3 lever light switch...you would need to pull the switch to test from there...let me know if that is an issue.

If you do have power at one post, then plug it back on the switch and have someone push the brake pedal or brace the pedal down with a heavy object or pry it down...you get the idea. Check to see if you now have power at both wires at the bake pressure switch.

If you dont have power at both now the switch is bad.

If yo do have power at both, you have a bad wire, or wires, from there to the rear OR both bulbs are burnt out OR their is a problem in the light housings.


I would bet, 75% or better certainty, that it is the brake pressure switch....

[Binford]

I would bet, 75% or better certainty, that it is the brake pressure switch....

That's what I was going to say as well. It's a $10 part, available at NAPA, if that's what it turns out to be.