OK, I had some time to troubleshoot the SOB (2001 Coleman Bayside pop-up).
Pulled the Dexter Axle info and the Draw Tite Activator II documentation from the info packet we got when we purchased it new.
Got the DMM out and disconnected the battery. Pulled the trailer connector apart to verify connections. Saw from the diagram that the connector matched the documentation with the axle info.
Brake wire is blue, ground wire is white, and 12 volt
wire from truck is black. Running lights are grey, brake lights are red and green. Center connector ( 7 pin connector) is unused.
Saw from my info, as the SOB is a single-axle trailer, that the two electric brakes should draw 6 amps.
Measured the resistance between the blue and white wire, and it read 2.0 ohms. 12 volts/2 ohms = 6 amps, so that resistance seems OK.
Checked the resistance between the white wire and the red, green, and grey wires. Got 2.5 ohms for the red and green wires, and 0.8 ohms for the grey wire (there are a bunch of running lights on the Coleman). This seemed relatively reasonable.
Checked resistance of the blue wire and the red, green, and grey wire. got 4.4, 4.5 and 2.8 ohms respectively. Looked OK, as it would measure the resistance of the lights in series with the brake magnets, I am guessing.
So, at first blush it does not appear to be a short in the wiring - I dunno.
I then Checked the break-away switch. It appeared to be open circuit when the key was in it,, and a close circuit when the key was removed. That seemed OK.
I left the trailer connector open, and re-connected the trailer battery. I checked for 12 volts between all the pins, and only got that between the white and black wires. The blue wire seems like it is isolated.
I crawled around, and saw that the brake wires (blue and white) is routed through the frame and axle. I wiggled both at the Y connection as it came out of the frame and into the axle. I also wiggled the connectors at each wheel. I disconnected the battery again, and checked the resistances, and they were unchanged.
I then made sure the trailer connector wires were screwed down tight. I put it back together, reconnected the battery, and looked at the truck connector.
I took it apart, and checked resistance between the blue and white wire -- it was unreadably high. I checked the wires for tightness and sprayed it with contact cleaner. I then sprayed the trailer connector with same. That looked OK. I checked the white wire and truck frame for ground. That was good.
I then checked the white wire on the trailer and trailer frame. It was good.
Ordinarily, I would hook the truck up and see if I changed the behavior at this point. However, the trailer is popped-up right now, and I did not feel like taking it down, so I crawled into the cab.
I saw that the Brake controller was not mounted firmly to the dash--it would do a fair amount of shaking. I took it off, cut the tie-wraps, unwound the black tape, and wrung out the connections. The white wire (again, ground according to the Draw Tite pamphlet) was indeed grounded, and I wiggled the connections, and they seemd tight.
I re-mounted it to the metal dash frame, and tied the wires back.
I plan upon folding it up in the next day or two and hitching it up to see if the wiggling and spraying and tightening affected the problem at all.
If it is not fixed, I plan on doing the following:
I have a friend with the same brake controller in his truck. I will borrow the truck and see if the problem repeats with his brake controller.
If it does, I will know the the fault is from the trailer connector rearwards. If it does not, I will install his controller in my truck and see if it repeats. If it does, I know it is in the truck wiring, if it does not, it is probably the controller.
If it is in the trailer, i plan on temporarily running two wires from the trailer connector to the y connections, and disconnecting the wire that runs through the frame. Then I will do the same with the wires through the axles, if that does not do the trick.
If it is still doing it, I will know it has something to do with the magnets, and will have them looked at by the dealer. Might as well have him repack the bearings, too.
I will update this thread when I work on it again...