Re: Am I doing something wrong!
That adapter won't help him at all because the 5th wire brought out is the brake control wire, not the back up light wire. Most of these adapters bring out the center pole of the connector to the 5th pin on the 5 pin connector. This is the blue wire which is brakes. Would have to rewire the vehicle to make this work. Better to make your own adapter with a a 7 pin plug and a 5 pin connector.
As far as a backup solenoid not working if you "goose" the throttle, not sure what you are talking about since the backup solenoid is really just a valve that prevents brake fluid from leaving the master cyclinder.
Relaying an experience that I had.....may or may not apply as the boat is MUCH heavier than the OP's.
To get into my garage, I have to back over a small curb, and then up an incline to get on the flat garage floor.
Doing this, it requires I "goose it" a bit to get the tires over this curb.
The first time I did that, the brakes locked up and I was stuck. Even though the proper wiring was in place with a 7 way to a 5 way....as installed by the trailer manufactuer and confirmed with the boat manufacturer.
It's my contention, and I could be off base, that this "goosing it" over the curb, with untolds amount of force and a heavy weight, prevented this solenoid from doing it's job.
It was always my understanding that this "5th" pin only provided "juice" to the electrically actuated solenoid valve on a surge system vs an electric braking system.
No 5th pin to another 5th pin....no juice to the valve.
For clarity matters, I believe you may be speaking of "electrically" actuated brakes vs. surge operated brakes, that do not use juice to actuate the brakes.
At one time, I had a travel trailer that was equipped with electric brakes and had a controller inside the cab of the tow vehicle. There was no "surge" involved and completely electric.....where your suggestion about a "brake" wire may come into play.
Good thread, as I am sure lots of guys have experienced this in the past and have wondered what the heck is going on.