Thread: Wiring a third brake light

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I am attempting to wire a third brake light into the wiring harness from a 1992 Suburban. (It now resides in a 1937 Cadillac). I am using a 1940 Fors tailight as the third brake light; it mimics the decorative chevrons that originally resided on the trunk lide.

How can I wire a third brake light and keep it from blinking when I turn on the turn signals?

Each taillight has a ground, a running light, a turn signal, and a reverse wire. I can plug in the running light wire, but if I use a signal wire it blinks when the turn signal is on. Do I need to run a new wire all the way to the brake switch? If so, do I just splice it in or do I need to find another power source?

Thank you, Jay

If there is no 3rd brake wire originally in the harness, you will need to run a wire to the white wire on the brake light switch.

What if the wires to the brake light switch are brown and grey?

the suburban wires at the brake switch are brown and grey. If there is any consistency in the wiring, the brown should be hot.

I use Mitchell on demand 5 and it shows the same thing that DennyW posted, orange and white. Are you sure the harness is from a '92? Either way, you cannot tie in at the lights. You have to have a wire coming directly from the switch to feed the third light. If the wires at your brake light switch are not orange and white, then use a test light as DennyW said to find the wire that has power when you press the pedal. If you don't have one they are cheap and are very much necessary when working with wiring, or you could use a voltmeter or multimeter. Test light is easiest.

if you have the third light mounted then you have the perfect test light. Make sure the light is grounded at the back and connect the wire that you run to the switch to one of the wires and see what happens, if it burns constant move it to the other wire.

OOHHHHH, you mean that white wire. I found the white wire and ta-da it worked beautifully. Thank you. I was looking at the suburban brake switch and I had assumed the plug with just two wires was the brake switch.

Does your manual tell you what the other wires running in to that switch are for?

I am glad we had this conversation because I would ahve been very frustrated when I went to transfer the wires from the suburban brake switch to the brake pressure switch I plumbed in to my brake lines.

Thanks again for the help.

Good write up =]

orange goes to brake/hazzard fuse, white goes to blinker switch, pink/white goes to ECM/Ignition fuse, purple goes to antilock brake module, according to my info anyway.