Did you actually test the switch with an ohmmeter, (have to disconnect both wires from the switch)? You may have a problem somewhere else. If it checks out good with the ohmmeter, then test it under a load, by hooking up both wires to the switch, but pull them back a little bit so you can get your meter leads on the switch terminals and set the meter for DC volts. Apply the brake and you can do this test one of two ways.

1. Put both of the leads across the switch terminals and your reading should be zero volts if the switch is good (current is flowing thru the sw, meter is pos to pos). If it's bad you may see a reading that is something like battery volts or less (current is not flowing thru the sw, your meter is now seeing pos on one side of sw and neg on the other side), depending on how crappy the contacts inside the switch are.

2. The other way to test under a load is to apply the foot brake put the black lead of voltmeter on your battery ground and probe each of the terminals on the switch with the red lead. If it's good, you should see 12 volts going in and 12 volts going out on the other contact. If it's bad you will have 12 going in and nothing or very little coming out on the other terminal.

If it's good, time to start ringing out the wiring to the light.

 

I put the bike up on the lift today in preparation for changing my fork sliders and decided to mess with the switch a bit. I removed the wires and checked the switch with an ohmmeter. With the pedal depressed, I was getting very close to a 0 reading.

I then turned the key on and shorted the wires together...Lights lit right up. When I connected the wires back up to the switch - Nothing.

After reading your suggestion, I took the meter to the switch and found that I have about 12V across the switch with the pedal depressed. I guess I need to replace the damn thing again!!

I guess the next obvious question is "why the hell are all these switches failing"??? The latest one was aftermarket, the previous 2 or 3 were HD.

 

Yeah that does seem odd that you've gone through that many switches. Is it possible that they are getting contaminated with brake fluid?

 

Last year I had to replace my stock rear brake switch (70,000 miles). I purchased one from my local dealer, for $65. 1 month later it failed! Apparently the replacement switches are prone to early failure. I went to my local auto parts store and found a replacement for $15. I've put 20,000 miles on since replacing it with no problems.

 

The first couple of replacements came from the stealer. The last one came from the indy.

I have no idea why they're failing so quickly. I had to replace my rear master cylinder early on, so everything including the fluid was new. I replaced the first switch a couple of months later when I found that it wasn't working.

I'll get another aftermarket switch in the next few days, but I have no idea why they're all failing.

 

What local parts store? also do you have the part # that you bought?

 

Okay so where is this post on purging the line?

 

The below was what I did to make a quick fix of getting the air out and the small amout of trash that could be at the edge of the thread of the old switch. If I thought I had trash in the line from repeated failure of the switch I would probably change out the fluid in the master cylinder and break the bleed a couple turns at the rear wheel and pump a couple master cylinder fills thru.

With the new switch close at hand, remove the bolt supporting the block if necessary to gain access. I need to do this on my softail since my block is back near rear tire. Newer bike are closer to the middle. Remove the two wires. Clean it off good at the exposed thread area of the switch. With a wrench to hold the block and another on the switch screw it out cclw. Let a few drops of fluid drip out to remove any trash. If you have a helper have them push the brake lever down very gently just to get a few more drips out. Do not let the brake leaver come back up. Screw the new switch in about 2½ turns. Should be engaged but have a little shake. Very carefully and gently push some more on the pedal till you see a few more drips. While still holding the pedal snug up the switch. Do not push hard when only engaged by a few threads!! Seems complicated but is really not. By doing it this way if by chance there is any crud it will be pushed out and not stick the new switch and you will bleed ever bit of the air out of the line. You are ready to go.

 

Did this and it worked like a charm. Damn switch went out on me right as I got it to the base safety inspection. Failed and I was fuming because I just checked it pre-ride!

Had to find a shop that carried it in stock and get it back in so I could continue the process of bringing it to Japan......Pain in the A$$

 

any 1/8 npt two pin pressure switch will work ..
I had the original HD switch go bad ..

bought one at NAPA( think it was for a old chevy) and changed terminals to match ,,,
still working after several years . cost about 5 bucks