I have had less than satisfying results with replacement pressure switches on these older vehicles. The big variable is the pressure required to activate the switch. And it is hard to find that data.
You want to get as low a pressure switch as possible because these brake systems operate at lower pressures than late 50's and 60's vehicles. A 100 psi switch (common on Fords) will not turn the lights on until you are well into the brakes on a '30's or '40's Chevy.
I finally found a NOS GM switch. It is a 30 psi switch so works much better. I am still going to go the same thing Tiny did and add a mechanical switch to my '37.
