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no brake lights have all other lights in 1941 chevy truck 6 volt system.If not pressure switch what else?

Have someone push on the pedal really hard or watch the lights while you do. If they light under extreme pressure it's the switch. On my '38 the pressure switch would get really stiff and I'd have to lock the brakes up for it to work. I got tired of replacing the switch every two to three years and replaced it with a later mechanical lever switch. If you remove the wires to the switch and touch them you should get the brake lights to come on. Apart from a broken wire the switch is about the only thing that could be wrong.

Relace the switch. Common problem especialy if you use silicone brake fluid.

Before you replace the switch make sure the brake lights work. Simply put a jumper wire between the 2 terminals on the brake light pressure switch. That should turn on the brake lights.

I agree with Tiny and Gene. There are lots of posts about failures of these switches Also my experience is that most of the switches you buy today take a lot more pressure to work than the original switch.

The wire for my brake switch, broke off where it comes out of the loom. Haven't figured out if that is the power wire or the one to the rear.

With a voltmeter or test flight you can check the wire that is still intact.

Connect one lead to a good ground. Touch the other lead to the wire that is not broken and still attached to the switch. If you have voltage or the light comes one that is your answer.

That is the plan. Haven't got around to it yet and it has been real hot here. 112 on Friday 8/14/20 and 113 on 8/15/20. I did pull the switch and it checked out good.

I will “bleed” the brake light switch to make it a little more responsive. That reduces the compressible air pocket between the master cylinder output chamber and the plunger in the switch.

Just replaced mine and while looking over the counter mans shoulder, I read the working description, 60-120 lbs.

I just got mine working a little while ago.
I used a volt meter and a wife on the brake pedal and light switch.
First I made sure it wasn't just bad contacts at the bulbs.
Then made sure I had voltage to the brake switch (mine is the mechanical one on the front of the toe board), and through the switch when the brake was depressed.
I was lucky and it turned out it was the connectors in the wiring harness from there back to the tail light.
Mine has the original wiring and there is a pair of those spring loaded turn and lock connectors inside the frame just back of the master cylinder, and another pair on the inside of the frame just ahead of where the wires go through a hole in the rear cross member to the tail light.
I used two pairs of pliers to lightly and carefully twist the ends of the connectors back and forth while pushing them together until they would unlock and I could pull them apart..
A little fine emery cloth, a can of contact cleaner and some patience, then packed it full of dielectric grease and reassembled.
The only reason I even thought to look for connectors was because the parts book said there was a separate harness for the tail light... so I went looking for connectors.
Ole

After paying $18.00 for a pressure switch at O'Reilly and having it go bad in about a year, I crossed some numbers and bought a fist full of old stock switches on eBay for $5-$8 each. I have not had any problems with the replacement switch O'Reillys gave me. I think it is the spare parts stash that is keeping my new switch honest.

Mike

Got problem fixed .Light switch and bad ground at tail light fixed problem.