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All of the rear lights work properly except for the left brake light. With the brake pedal pressed down, at the connector where the rear lighting harness plugs in, I am getting ~12V to the Orange/light blue (right side) wire and ~2V to the Light Green/orange (left side) wire.
Looking at the wiring diagram, it looks like power runs from the brake light switch (on the pedal) to the directional switch (turn signal) and then from there to the rear of the truck.
Am I correct in understanding that brake light power runs through the turn signal switch?
If so, am I way off base thinking that my turn signal switch might be the cause for the low voltage?
The truck sat up for 15 years until I put it back on the road a few months ago, and I’ve come across a few rusted/corroded connectors and switches through the project.
Am I correct in understanding that brake light power runs through the turn signal switch?
Yes it does.
Originally Posted by Revnate
If so, am I way off base thinking that my turn signal switch might be the cause for the low voltage?
It's plausible. Seen a few of those multi-function switches grow green corrosion on the contacts. Also see the same green corrosion in the connectors/pins. Worth a shot to check those in the brake lamp circuit path as well.
Since the turn signal works, with or without the brake pedal depressed, the combination switch is the problem. Brake-light contact on terminal 9 (LG/O) on the Combo-switch is not allowing current to pass.
Or a connector on the path to the bulb is bad/open wire.
Thanks much! I’ll check for continuity from the switch to the bulb terminal and if that checks out, I’m going to replace the switch. I appreciate the info.
Thanks much! I’ll check for continuity from the switch to the bulb terminal and if that checks out, I’m going to replace the switch. I appreciate the info.
You might try flipping the turn signal stalk between "left-turn" position and "Off" position 100 times. It might be enough to rub off the corrosion and create a good contact, saving yourself time and money.
I'm going to toss another vote in the hat for that combo/multifunction switch, I had almost the exact same issue a year or two ago. The little copper contacts inside the switch had almost totally oxidized over and turned green.
For the sake of holding onto a couple of bucks, I removed and disassembled the switch and cleaned the contacts up with a wire brush, got them shining like a brand new penny! Reassembled it after lubricating all the plastic on plastic friction points, and it still works like it's brand new!
It’s definitely the switch. Thanks for all the help.
I got to work on it some today. When the switch is in the center position, I can wiggle it a little and the brake light will come on. I’m guessing it’s more an issue of fatigued plastic than one of corrosion. But at least we got it narrowed down.
Thanks again.
Just an update- still dealing with the same issue even after replacing the turn signal switch.
I can lift the turn signal switch handle just slightly (moving toward “right turn”) and my left brake light will come on with the brake pedal is depressed. But if I release pressure from the handle, the brake light will not function.
I had believed it to be the switch itself. And if it wasn’t, I can’t understand why moving the switch handle would make a difference.
So I’m still at a loss. Is there anything else in the steering column that could be loose or corroded which could cause this?
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