I bought a Tekonsha P3 Electronic Brake Control for my Ford E350 van. The instructions contain a warning sheet that says on some vehicles when the manual control is used the stop light switch can ground the circuit and destroy the unit. I tested the circuit with a high impedence multimeter and brake switch not activated. The readings were 1.9 ohms with ignition off and 2.9 ohms running. The wiring diagram for this van says the brake pedal switch also directly powers the high mount (3rd) stop light while signaling the Powertrain Control Module (PCM) and the Smart Junction Box (SJB). Supply to the pedal switch is Hot At All Times fused 10 amps.
So will the unit be destroyed if I activate the Manual control with the ""red" wire connected directly to the Brake Pedal Switch? If so, can I install a diode or diodes to prevent "Manual" activation current from trying to power the 3rd stop light circuit?
Is there another suggested source for the brake pedal signal or if a diode won't work, can I put in a relay to isolate the Tekonsha brake switch signal when the brake pedal switch is not activated?
The above is a direct quote of a question I asked via the Contact Tekonsha website, I'm repeating it here because it's a Saturday night and I don't know if they answer that kind of question for DIY people. I'm wondering if any of you know the answer, or if you are sure I don't have to worry about it. The warning sheet has a work-around for 1998-2005 models that hints maybe 2006 & up are fine as-is. The copyright on the sheet is 2011. I'm thinking a single LED light might not kill the P3 but an array of HIDs would be as good as a short to ground.