I've done a search for potential solutions, but I'm stuck.
The taillight stays on with it just sitting there. But if I push the lever out a little, it goes off. The front brakes are tight and respond really well, with not much play in the lever. I did use a shim when taking off the master to check it, and the boot on the switch itself looks solid. And yes, the master and the switch housing are snug up against each other. With the master off, I can click the front switch in and out to get normal operation. Almost seems looks either the spring in the master piston isn't fully returning the lever to kick off the switch, or the switch itself is shifted back in the housing.
So my options are to gut the lower switch housing to check that it's fully seated, or replace the piston on the master (or stretch the spring a bit, which seems like a bush league fix).
I need to get this working before the Memorial Day ride to Yosemite! But I can't ride it will the light on (not legal OR safe!)
Thoughts?

 

It's an 03, how many miles? when was the last time the Master cylinder had a rebuild? ever? The light goes out when the piston pushes the tip of the switch in. (activated) Just not doing a full return after actuating the brakes.

I'd buy a switch too, just in case. It could be they are both slightly worn and it doesn't take much for that switch to not work.

 

About 45K miles, and I doubt the master has ever been rebuilt, so a new piston kit isn't unreasonable. It's just that the action is really good, and the lever "feels" like it has a little play in it compared to the new ones at the dealer. Last Spring I did a full brake job, with new rotors, and really cleaned the caliper Pistons. It's not spongy at all in front, just the minimal play I mentioned.

 

Just because pictures are cool!




New rotors





Around town style





When my wife comes along...

 

The plunger on the brake switch probably is worn out, and needs replaced, or it is in a bind.

 

The little nipple broke off the tip of the brake light switch on the bars. Mine did the same thing when I accidentally broke it changing bars. Drag Specialties has one for $16.00 and HD has one for $60.00. For obvious reasons, I went with the Drag Specialties and it works great.

 

Done! I bought a new master piston from HD for $40, some fresh DOT 5 and some spray cleaner. The button on my switch seemed intact, so I just hoped it would work...
45 min later, I had the whole thing cleaned, and the piston kit installed. Remounted, and the brake light works perfectly.
I learned a trick from a master mechanic a while back: pull back the lever after pumping it a few times and zip tie it overnight. THEN bleed at the caliper the next day. Air bubbles in the line will mostly travel up and you can cut your bleed time by 90%.
By the way, the "small amount of play" I had in the lever is completely gone.
Looks like I'm making the Yosemite trip after all....