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TR2/3/3A TR3 Brake Lights

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PSUTR3B

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Its a 1962 TR3B. Both brake lights suddenly stopped working. The tail lights are fine. At the switch it registers 12V and when the pedal is depressed it goes down to 8.5-9V. I think I need to replace the switch. Any other tests I can try and anyone have a thought of any other problem it might be. Thanks!
Gary
 
I would certainly try cleaning up the connections at the switch before replacing anything. You may need to strip the wires to expose cleaner copper or just replace the little harness. I tin the tips of the wires to get better contact.

On second thought... perhaps later TR3s have Lucar connectors here rather than the screw posts in which case cleaning may still help but tinning is n/a.
 
The TR3 uses a pressure switch and is a common failure point. You can try to remove the switch and clean it inside with brake cleaner and compressed air. I had to replace mine because it started to take too much pedal pressure to be useful. Easy fix. Located on pass side of the frame under the carbs.
 
The Bullet connectors are problematic on these cars, I would take them apart and thouroughly clean each suspected one, especialy in the trunk area and the switch, also the bulb holders inside of the Lucas tail light leave a lot to be desired. Remove the bulbs and clean the bulb contact connections also. Ensure that the wires are making good contact to the bulb holders inside the tail light. If this proceedure fails to remedy your problem try another switch.
 
When mine failed, I installed a 30 amp automotive relay in the circuit so that the pressure switch was not switching the high amperage of the brake lights. Installing the relay caused my failed switch to work. I have since installed a new switch, but the relay also increases the life of the new pressure switch.
 
I also suspect the bullet connectors, mine were always covered with a powdery residue, if you pull the chrome assembly out, try a continuity test, ground check and if it is a short harness from the main, check the bullet connectors there as well and clean to avoid future issues. On some occasions when all passes the above tests, the actual socket is the issue. The same residue coats the two contact points for the base of the bulb quite often. Test continuity to those points to eliminate that as the source of course.

Best Regards,
Brian
 
With the pedal released, you should only see 12v on one side of the switch. The other side should be at ground.

If the hot side drops to 9v with the pedal depressed, there is a poor connection somewhere in the wiring (or possibly a bad ignition switch). I would check next at the 'green' terminal of the fuse block, to see if it also droops when the pedal is pressed. If not, the problem is in the green wire from the fuse block to the brake light switch; possibly in the bullet connector above the switch.

If the 'green' terminal on the fuse block does droop, then the problem is farther upstream. Next place I'd check in that case would be the 'white' terminal. And so on.

Now that you've dealt with why the supply voltage droops, what does the load side of the brake light switch do ? If it's the same as the supply side with the pedal depressed, then the switch is probably OK. If not, the switch is bad.
 
RedTR3 said:
When mine failed, I installed a 30 amp automotive relay in the circuit so that the pressure switch was not switching the high amperage of the brake lights. Installing the relay caused my failed switch to work.
Click to expand...
That's a very interesting comment, wish I'd tried that. After about the 3rd pressure switch died in as many years for me, I converted to a mechanical switch (ala TR4), but being careful to select a switch from a car with a "high center" light (for increased current rating). Worked great, but the wires across the engine compartment are kind of ugly. I'll try a relay next time.

Thanks !
 
Aloha,

A simple test to see if it is the pressure switch is jump over the switch. A small length of a test wire with alligator clips at each end is handy for this. Connect each of the two terminals on the switch together with the test wire. Turn on the ignition, if the brake lights are on, the switch is the culprit. If they are illuminated, the problems is else where in the circuit. Another handy electrical test tool is a 12VDC lamp (I use an old speedometer lamp) with about 2 ft wire leads and alligator clips on the ends. You can use this to trace a circuit with one lead clipped to various connections in the circuit and the other end to ground. If the lamps lights, power is getting to that connection. Moving along the circuit you can determine where the power failure is. Most common LBC electrical problems are a bad path to ground (earth).
 
Dave
I tried the alligator clips across the brake light switch and the brake lights went on. If I push the pedal hard the brake lights do come on. The harder I depress the pedal the brighter the lumination. If I correctly understand, the problem is the switch? In removing the switch will any fluid leak out? Thanks for your help.
Gary
 
Aloha Gary,

I would recommend replacing the switch based on your test results. It is my experience that I need to replace the switch every two to three years. I believe that is caused by the relatively high DC current load on the switch. As RedTR3 suggests, installing a relay may extend the switch life.

There will be some fluid leaking during the changing of the switch, but if you work quickly it will be minimal. You may not even need to bleed the brakes.
 
My TR3 brake lights quit working just before I took it off the road. It was the switch. I cleaned it up and bought some time with it, but I think replacement will be the only fix.
It is so close to the exhaust and high heat along with dirt, grime and everything else that gets thrown at it. It would be worse than being a Cleveland Brown!
 
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