Master Cylinder Brake Switch

I'm working on a 72' 750 project from scratch and don't know what worked and didn't before this all started. After bleeding my front brake I connected the power wires and the brake light stays on. I know it's a pressure switch normally open, when I put my ohm meter across the switch I can activate the meter by using the brake lever like it's supposed to work but not with power to it. The rear switch is new and works fine. I used a jumper wire across the two switch wires and that will work the light. Any suggestions :?
The inside of the switch is as clean as I can get it after flushing it with spray cleaner.
I tested a spare switch with my meter and it shows a short across the terminals so I assume it's junk?


Tim_S

Yep if it still conducts with12-ish volts on it, toss it and get another from BI or Harley vendor, but sometimes on '72's, like mine, the switch terminals are round bullets not flat spades, so to avoid making new wire terminals, if yours are round try BI vendor first and ask about the terminals.

Let me rephrase this issue ,,,,, My switch is attached to the master, I put my meter across the terminals and I can trip the meter by pulling the lever. I jumper the power wires and it trips the light. I connect the wires to the switch and nothing happens. :? Sometimes simple isn't simple..... or is it just me

Tim_S

Tim, Check that your switch connectors are not earthing through the body of the master cylinder, they should be completely isolated, but if earthed then the power to the switch will go straight to earth rather than to the brake light feed wire. Use your multi meter to see if there is continuity there between switch spade-connectors and switch body.

I didn't think of that Dave ! Terminals are nice and tight but no contact through them to the body. Good idea though ......

Tim_S

Tim, Then I can only think that there is a high resistance with the internal contacts, it may show continuity with an Ohm meter but doesn't actually allow any power through it. I think you've done all of the appropriate checks and a new switch is called for.

Dave ,,, I did one more test. I hooked a battery to the switch with an inline light bulb, no glow. Junk switch........


Tim_S

New $30 switch cured the problem ,,,,,,, If only I had known and consulted the group? :roll:


Tim_S

Tim_S said:

New $30 switch cured the problem ,,,,,,, If only I had known and consulted the group? :roll:


Tim_S

Click to expand...

Only ten days from the last bit of solid advice. Probably raining where you are so no riding anyways, right? :mrgreen: