If the combination valve fault switch is replaced, will it be necessary to bleed the lines? This is just removing the old switch and replacing with a new one and not doing anything else. Based on the cut away diagram it appears that the region where the switch goes is sealed off from the front and back circuits.

 

Generally speaking you should not have to bleed the brakes. No fluid should escape. If it does you need a new valve.

 

^^^This. There should be no fluid in the part of the valve where the switch contact resides. The bigger question is, why do you think you need to replace this? The "switch" is just a solid metal contact inside a plastic housing. The actual "switching" takes place when you lose pressure in one side of the brakes, which forces the internal piston against this terminal, closing the switch and illuminating the BRAKE light. There isn't anything in that part to go bad.

 

I have to remove the switch to jiggle the piston. My light goes on and off with varying brightness that started after I flushed the brakes. I let it go for awhile to see if it would go out permanently with use but it didn't. I figure for about $10 I might as well put a new one in there since I'm messing with it.

 

Sounds like the piston still isn't centered.

 

Sounds like the valve needs to be centered, not the switch replaced. Or... your losing fluid for one reason or another.

 

Yes, I agree that the piston needs to be centered but the way I figure it I might as well replace the almost 50 year old switch with a new one while I'm in there.