I am replacing the ever-sketchy setup on my boat trailer. Trailer came with a 5 pin flat plug, SUV has round 7-connecter deal and the adapters have just never worked reliably. Replacing the trailer side with a 7-pin tail.

I can sort out which color/position wire on the flat connecter goes where with the following exception.

Trailer has (non-electric) hydraulic disk brakes. There is a solenoid that bypass these when backing up, otherwise you'd not be able to since the tongue on trailer would compress and "brake" the wheels.

For the circuit on the trailer that operates that bypass, do I use the "reverse lights" pole on the 7-pin layout? I think that's my only choice, doesn't make sense it would be the electric brake pin.

Any insight much appreciated!

To the best of my knowledge that how it is on my boat trailer (although my Ranger trailer came with a 7 pin/round connector). I bought a trailer mover with a brake bypass for moving the boat/trailer and it activates the backup lights to bypass the surge brake.

Yes, wire the solenoid in parallel to the back up light. The other solenoid wire goes to ground. Should not matter which is (+) and which is (-).

Thanks guys. The current wiring harness has three separate blue wires going to the 5th pin, those will be the ones connected to white/reverse in new setup. No idea why there are three of them....

quote:

Originally posted by Georgeair:
Thanks guys. The current wiring harness has three separate blue wires going to the 5th pin, those will be the ones connected to white/reverse in new setup. No idea why there are three of them....

Likely one for the left reverse light, one for the right and one for the reverse solenoid. It would have been cleaner for the trailer manufacturer to run just one wire up, but this is likely more reliable/durable/easier.

When rewiring trailers I've found that running full length runs (+ and ground) to each light ends up being much more reliable in the long run.