If you pull the switch, better have a new one handy. They are install, and adjust ONCE, after that, it's junk.

 

While that is what the instructions say, it is not necessarily true. If you pop the plastic cover off (easy to do, just 4 clips), you can reset the "automatic adjustment" plunger.

 

Man, I was sure it was the switch. Would rather be that than wiring. Can you do some continuity testing on the wires from the MFS to the tail lights?
The Brake Switch voltage should go right thru the MFS with it in its neutral or center position. If you get that working, use that to find if there is a wiring problem.

 

If the third brake light is working, I'm pretty sure it's not the switch.

 

I was talking about the MFS, but you did just say that the brake switch killed your battery, and you were checking it. Great that it's working. You can trace that brake light voltage to and thru the MFS to the tail lights and even to the trailer connector. Do you have a test light?

 

Yeah, I have two meters (both pro quality) and a test light, mainly from owning old British motorcycles. XD

Yeah, the switch stuck in the on position and since the third brake light was working it stayed on all night and flattened the battery. Battery is recharged now and I'm going to do more probing and start mapping the circuits for voltage to compare to what they should be, try to see where it's not getting signal.

Also going to make a jumper from battery and power up the stop/turn bulbs to make sure they're working on that end so I don't chase my tail too hard on that.

 

That's good to know. Thanks.

 

Gotta love Lucas Ignition.

 

Imagine my chagrin when I opened the steering column to evaluate the MFS and saw the Lucas logo on that switch.

 

As crappy as their reputation is, I am just stunned that they are still in business.