Technical HYDRAULIC BRAKE LIGHT SWITCH LOCATION

Your questions might be missed on the first page. That idiot light is actually the brake warning light that comes on if one circuit goes bad. By the way, there is a spool shaped piston for that light and when bleeding a new install, the piston can easily move to one side during the start of bleeding, which will drive you nuts when you try to get any fluid from the second circuit you bleed. That spool often won't allow fluid for the second circuit unless it moves back on it's own or if you lock it in place while bleeding. Just a heads up.

Anyways, you'd need two hydraulic switches to make it legal. One front and one rear, just like old air-cooled VW masters cylinders had. If you only put a single switch, such as on the front circuit, you lose brake lights if the front system goes out...or vice versa. So, you'd need two inline tees, and two pressure switches...or..

We don't know where your master and pedal will be on a custom build, but most people here would use a mechanical switch rather than twin hydraulic ones. If under the floor, it needs to be waterproof, so that adds to the drama of getting the correct switch. On stuff I did for decades, I always used a Chevy truck switch from the 60s early 70s and they are dependable and very adjustable. Might likely be same switch on Chevy / or Gm cars too. They are not waterproof, they are used under the dash.

 

Harley Davidson makes a brake light switch that is as good as the old ones. Available at any Harley dealer.

 

Yeah I kinda thought so but didn’t want to start a new thread if I didn’t need to. But back to the question, I do have a tool to lock down the circuit so I can do the other side but this is all new to me. Disc conversion up front and drums in the rear. It’s a 1951 Ford so the master is under the floor. The original switch was under the floor on the rear of the master cylinder so I was going to put a tee in the front circuit and run it like that. I noticed that there are residual valves in the original post do I need them to or does this new fangled block have them built in.

 

Not in the block IMO, they normally are installed in the outlets of a typical OEM factory installed master cylinder.

Take the lines off the master and look in each outlet. OEM factory masters usually have a brass tapered pressed-in seat that holds the residual valving in. Someone on here said to very lightly press in with a small blunt tool to feel if they are there. I'm thinking just take a look, rather than disturb something.

Wait and see if others have more accurate info on the aftermarket systems like yours seems to be.

 

Painless wiring has a reliable one too, it was $27 a few years back.

 

You won't disturb the brake warning light "piston" if you vacuum bleed your brakes .

 

When I first built my avatar roadster, I used a normal hydraulic brake light switch with silicone fluid. I went through several of them. I switched to hydraulic brake light switch from a Harley and never had another problem. Harley uses a hydraulic switch made for silicone fluid and mine has performed reliability since being installed in 2010.

 

The kit that I’m installing in my car states not to use silicone brake fluid. Not a big deal for me because I have a plethora of DOT3 at my disposal