• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Trailer Light converter

Not open for further replies.


New Member
:mrgreen: I have been trying to design a circuit to operate a 4-wire trailer light system from a vehicle with 5-wires (L-Signal, R-Signal, Tail Light, Brake and Ground). Trailers currently use the same bulb filament for brake and signal, where the newer vehicles have separate bulbs for each function. Having no luck and hope someone might have an idea... Thanks...


Active Member
Hi duder,

This is something that came up years ago.
me and my mate tried to do it with three wires,
using the chassis return through the metal.

We found the return through chassis unreliable.

This was the easiest we came up with.

The diode may not seem necessary at first,
but we had to include it because the brake light
circuit in this country is fed from the ignition.

We found that the engine sometimes would run-on
after being switched off.

It wasn't long before we realised that this only
happened when the ignition was turned off,
with the footbrake pressed, and the lights on,
this caused a back feed from the lights into
the ignition circuitry.

So an appropriate diode cured that problem.

I vaguely recall we made special arrangements for
the resistor. I think it had its own little mounts
and cage positioned somewhere. It got hotter than
we thought it would. We should have made a bigger
one. Dont remember much about that.

If you find a better or easier way,
i would like to know about it.

Regards, John


Not open for further replies.

EE World Online Articles