At 05:48 PM 7/13/06, Douglas E Starns wrote:
"My 1960 MGA 1600 brake lights don't light up until the brake pedal is depressed with a lot of pressure .... How is the sensitivity of the brake light switch regulated? I.e., how do I get the brake lights to go on as soon as there's just slight pressure on the pedal and the brakes just start to work? .... The switch is new ...."

You should be able to press the brake pedal with two fingers and make the brake lights work. This is nothing new. It's a faulty pressure switch. Send it back. If enough people send the junk back the vendors might eventually supply good ones.

The pressure switch in my car was working well when I bought the car at 150,000 miles. I don't know if it was original or not. I changed over to DOT 5 fluid during restoration of the car. The switch only lasted another 120,000 miles after that (270,000 miles in 40 years). The replacement switch purchased early 1997 is still hanging in there after another 80,000 miles (130,000 miles in 16 years as of June 2013). I had purchased a spare switch and carried it in the door pocket for a few years, but un-needed it went to the spare parts shelf where it is still collecting dust.

The problem with some recent new pressure switches is really cheap internal contacts which are not designed to carry the appropriate current load for long life. They usually work when new but may quickly burn contacts and deteriorate with normal use. As the contacts deteriorate they have higher electrical resistance, and require more pressure to get good enough contact to pass the current. Many will fail within months or weeks, and some may be bad right out of the box.

If you get a new pressure switch which fails prematurely, try a different vendor for the next one. Local auto parts stores can supply the parts. Early 1960's GM cars come to mind. NAPA-Echlin part # SL144 works, but I have mixed reports about that one too. They are under $10 (USD), so maybe keep a spare on hand. You might install a relay to off-load the current from the switch, but that's treating the symptoms rather than fixing the problem, and it adds more parts and connectors which could also give future problems.

The NAPA-Echlin SL144 is the grub screw version. It's strictly an LBC switch, i.e., 55-63 Austin, 48-64 English Ford, 51-56 MG, 49-64 Morris, 48-64 Rover, 49-64 Singer and 50-64 Triumph. Their SL147 is a blade terminal switch with a similar LBC list including 57-70 MG.