Brake Light Switch

M38MN · Post by **M38MN** » Sun Sep 22, 2019 6:11 pm

I'm on my 3rd new brake light switch. Lights and wiring are good, verified by using a jumper wire. With no continuity across terminals I bought a new switch. Installed with the same results. Called in a friend, we verified we had fluid by slowly depressing the pedal with a finger over port and it moved the finger and shot about 8" or so. Determined it was a bad "new" switch. Got replacement with same results. Got another from different store with same results. Filled the switch with fluid to maybe help? The 3rd switch is a NAPA SL134. Thoughts?

Post by **wesk** » Sun Sep 22, 2019 8:01 pm

Are you saying that with at least 40 or 50 PSI of brake fluid pressure an ohm meter indicates no continuity across the switch's contacts?

Some hydraulic brake systems operate with as much as 600 PSI. 1 or 2 PSI can make an 8" squirt. If you do not have a way to accurately pressure test all three of your switches, save yourself a lot of time and money and take all three to an automotive shop that can do the pressure check properly checking contacts with an ohm meter.

jnissen · Post by **jnissen** » Sun Sep 22, 2019 11:15 pm

Ran into a faulty switch in our rebuild and replaced it with a different one and it's been working just fine. Are you sure of the pressures the switch is seeing? If your brake cylinder is not properly pressurizing the brakes then it likely will never have continuity and more importantly your brakes will never work!

Be careful not to over tighten the switch. I used a large socket and was careful to not get overly aggressive with the ratchet wrench. These things really can be damaged if you use and open end wrench and twist or distort the metal while you torque it down. I could see that causing a problem.

I'd roll the dice and get another new one. Use a full socket and ratchet to install the new one. No need to put gorilla strength on the thing.

M38MN · Post by **M38MN** » Mon Sep 23, 2019 7:24 am

I have not checked the pressure from the Master Cylinder. I did a check ride with the previous owner and at 45 MPH the brakes (which are all new) worked well. When driving around (after buying) down a hill they seemed good. And yes ohm meter indicates no continuity across the switch's contacts. All were installed/removed with a socket and short ratchet to a good snug no leak fit. I doubt I'll find a shop to test the switch(s) but wil try.

Post by **wesk** » Mon Sep 23, 2019 8:37 am

And yes ohm meter indicates no continuity across the switch's contacts.

My complete question was:

Are you saying that with at least 40 or 50 PSI of brake fluid pressure[/u] an ohm meter indicates no continuity across the switch's contacts?

M38MN · Post by **M38MN** » Tue Sep 24, 2019 8:43 am

I plan on renting, borrowing or buying a pressure test set and verify the pressure at the port before I continue on with any more switches. I'm thinking I may still need to get a low pressure switch [closes @ 45 PSI]. I did some reading on the switches that I've had and although listed as 60 PSI a couple of users have tested them and found that they are closing closer to 80 PSI.

Post by **wesk** » Tue Sep 24, 2019 10:03 am

You do realize the switches will also respond to good old compressed air. You just need to assemble a collection of necessary adapter fittings and be sure you have an accurate pressure regulator and gauge.