Hey RRLund

was hoping to see a success post from you saying you got those trailer brakes working!

Waiting for Royce to get back home and post about them. He left here about a half hour ago. Since he's the electronics guy I'll let him get in to it. We made some progress and got some numbers,but still scratching our heads.

Think it's going to be wiring trouble, more than likely the ground wire somewhere.

yep, where it connects to the frame the nuts 'r rusted.

Thinking more on the pickup end he already checked out the trailer.

Well, I was off goofing around with other stuff. LOL

The first thing we did was hook my truck to it instead of his.
The brakes do not work right connected to either truck.

They don't sound the same, mine causes the brakes to buzz.
It does that on every trailer I've hooked it to. Mine is an electronic
controller where his is wet line operated from the master cylinder.
With his controller they don't buzz, but they click, and seem
to actually work slightly better than with my controller.

We hooked his truck up and took the factory splice (twisted/taped wires)
apart at the first brake to check voltage at the wires coming from
the front of the trailer.
With the other three brakes connected I got 6 volts.
With no brakes connected 12.6V. (same as the connector on the truck with no load)
With only one brake connected 9V.

It has been raining most of the day, so we didn't take voltage
measurements with the other truck.
I did take resistance measurements of two of the magnets.
They were 3.7 ohms while disconnected, which seems normal to me.

Plan is to re-do the connections at each wheel. They are fairly corroded.
Still seems like there may be something upstream wrong as well.
Any other suggestions?

You've got a bad ground or power wire. A trailer that age can have a bad spot anywhere along the wire that will get corrosion in it and cause that. I bet if you power the brakes for a bit then feel along the wire you will find a warm spot. I would rewire the brakes and run 2 wires all the way because grounding trough the frame can also be the cause of what you have going on. I always buy a cheap 2 wire orange extension cord to wire the brakes, just clip the ends off. It's usually cheaper than auto wire rolls and is better wire and has the protective coating and is easy to run.

Thanks Jon, might not be a bad idea to run a new cable.
I forgot to mention the wiring is already as you say.
It is one 2 wire cable ran from the front of the trailer to each of
the four brakes.
Brakes grounded through the cable not individually to the frame.

It is run inside the framework of the trailer, but if that cable will move easily
we could just solder a new one to the end and pull it through using the old cable.