Harness has to be busted somewhere if you have done all that and nothing is happening. Why, who knows? Has to be corrosion.

If you are really that tired of it, find the brake light feed wire in either the LH or RH tail light cluster and T tap (yes, T Tap- keeps the integrity of the wire you are branching into ) off of that and run new 18GA wire to the bulb in the 3rd brake light- cut and splice into the wiring harness for the 3rd eye. Hide it in the package tray, and secure the T-tap connector with a wrap of electrical tape.

Problem solved.

rjp

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03 540I (GAK!!)
81 280E (W123)
70 LeMans Sport with pissed off Poncho 462"
1989 Silverado Step Side (under the knife- complete restomod)