Re: Automotive Question: Trailer Brake Wiring (please don't read if you hate me and-or don't like factual posts)

Nza wrote:
I am wiring a new trailer brake controller into a truck that has had
one for a long time, but has burnt the wiring harness because of
poorly wired accessories, not to mention inadequate gauge wiring to
the circuits in question. Every resource I have consulted, including
the instructions for the piece of *** trailer brake controller tells
me to patch into the brake light switch of the truck. I find this
to be a bunch of BS. On this particular truck, I found wires melted
together at the brake light switch... probably due to the
controller.

The signal from the brake light switch is just a control signal, the high current is only on the +12 and ground lines. If something melted, then perhaps the old brake controller was wired incorrectly, since the current through that line should have been quite low. Or perhaps other accessories were wired into the brake lights, i.e. too many extra trailer lights, back up alarms, higher wattage brake light bulbs, etc.

You could always add a relay to the brake switch signal. Why don't you wire it as indicated and measure the current draw through that wire. If it's more than a few hundred mA, then add a relay to the circuit. If it's less, then don't add the relay as you'll just be adding another point of failure for no reason.

Also measure the total current through the switch with all the accessories and lights that run off of it. If it's more than a few ampa, then add a relay to the entire circuit; everything that is run off the switch.

Get a sealed automotive relay, with an internal diode across the coil terminals. Don't cheap out with a fog light relay (I've had two of the ones supplied with PIAA lights fail).
.

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