My van, like many newer vehicles, don't like extra brake and turn signal lights for a trailer simply tapped into the existing wires.
I had a special unit hooked up which made things work, but it burnt up last week. I could wire in a new brake/turn light unit, but with that unit, between it's internal resistance and the overloading the little wires made to power only 1 or 2 bulbs, there was quite a voltage drop and the trailer lights were often dimmer than I'd like. (The voltage drop was over 2 volts in certain situations.)
I thought this would be easy with some relays, but I ran into problems.
First to power the trailer, I ran a fused hot wire from the battery junction box to the rear of the tow vehicle (van) and I have a good ground off the van.
Keep in mind that the van has separate lights for brakes and turn signals and the trailer uses the same lights for the brakes and the turn signals.
I first wired in the turn signal lights tapping a relay into the vans turn signals, they work great! Nice and bright! Then for the brake lights I wired another relay with 1 diode going to each brake (and turn signal) lights. I used the diodes to isolate the two separate turn signals.
Now the brake lights work great and bright!
But I forgot about 1 thing. When the brake lights are on, I need to be able to make the trailers turn signal/brake light flash, which they don't since the brake relay in on.
I believe I can do this using the normally closed terminals somewhere, but my thinker isn't thinking as well as it used to.
Any help appreciated! And remember the tow vehicle has separate turn and brake lights, and the trailer uses the same lights for the brakes and towing. I think when it's done properly, I won't need the diodes either, but hey, I'm asking for help so I'll shut up!
Thanks, Tony