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TR2/3/3A Brake Light Switch

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M

mxp01

Jedi Warrior
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Gentlemen:

My brake lights do not come on when I apply the brakes. I had this repaired previously and have driven the car very little (a lot of time passed, but little driving). I have a few questions:

1. Is this a common failures on TR3s?
2. I see the electrical switch on the hydraulic line union and where it connects into the wiring harness. Is this the only connection?
3. I have looked under the steering wheel and around the pedal box, but have seen no additional switches. Is their another switch here to activate electricity to the tail lights?

Please let me know your thoughts,

Mike Pennell
 
There is no additional switch. It starts with a green wire from the fuse box, goes through the hydraulic switch (changes color to green/red) and on to the brake lights. There's a connector before the switch, and one after it. The ground is at the back through the body, a common source for not working.

Here is a wiring diagram...
https://www.advanceautowire.com/tr24a.pdf
 
It is probably the switch (the one you see on the hydraulic line). A quick test is to remove the two wires and touch them together (ignition on as I recall) and see if the brake lights come on. If they do then the problem is that switch.

Originals lasted a long time - replacements not so much so. There are various brands available - the Asian versions seem to fail sooner, the German versions (FTE) last longer. I think it is the same switch that was used on VWs -- if someone can confirm that then you will have more options for the replacement.

One can usually swap the switch w/o losing enough fluid to matter (if you're quick about it) and thus, perhaps no need to bleed.

One can also fit a mechanical switch to take over the duties. Even Triumph went this route with the TR4. Apart from getting away from the failure prone hydraulic switch, the mechanical switch can be set with a hair trigger - coming on with the slightest touch of the pedal. Sometimes an aging hydraulic switch will still work but only after you have really romped on the brakes.

I still use the hydraulic on the TR3 and also use DOT 5 - but I also added a relay to the circuit since I have 5 brake lights instead of the original two.

I did fit a mechanical to my other British car using a Volvo switch available on Amazon:

BrakeLightSwitch_zps467bf20e.jpg


I haven't examined it but quite possibly that mechanical switch could even be fitted to the master cylinder bracket using the holes left over from the deleted stop-bolts. Not stealthy but easy to set-up and adjust.
 
My hydraulic switch was replaced with a plug -my system is Silicon fluid.
I have a switch fitted to the pedal as Geo shows, but the quality of my switch is not so great. I'm on the third one now and it takes weeks for O'Reilly to get a new one. Lifetime warranties aren't worth much when they fail and you don't notice.

Geo, can you tell me the part number of the one you are using?

Mine is O'Reilly P/N 18-1980 while 8615K and 35350-679-003 made in Taiwan is also on the box.
 
I also had a lot of failures with the stock type switch, which may have been related to usage of DOT 5 silicone fluid. On my previous TR3A, I mounted a mechanical switch (from FLAPS) in the holes in the MC bracket (which were for stop bolts on earlier cars)

Worked great, but kind of ugly and obvious with the hood up.

So when the original switch on my current TR3 quit, I made up a bracket to mount the mechanical replacement under the dash. This photo shows a generic replacement from FLAPS, but when that failed as well (after a few years of daily use, likely contaminated with DOT 5), I used a TR6 switch from TRF. It has been in daily use for over 5 years and still going. (However, I have added relays, so currently the switch only controls two relay coils and about 10 watts worth of LEDs.)



PS, in both cases, I just left the original switch in place to plug the hole. no problems there. But I believe it is a standard 1/8" NPT thread in case you want to use a plug instead.
 
Thanks for all the input, guys. I ordered this new part through Amazon. I think I'll see it on Monday. Hopefully, that will make all the difference in this case.
 
Installed the new switch today. It is a much better switch. One issue I had with the other switch involved the physical "load" of the wires. If the side force placed on the lugs changed (because of a wire moving), so did the on/off point of the contacts. The lugs are tight on the new switch and impervious to wire movements. -It actually weighs 10g more tho it's an inch shorter. Thanks for the link/part reference.
 
Glad it seems to be an improvement. Time will be the real test.

Interestingly the original mechanical switch used on TR4s was made by Delco - not Lucas. It was made in England of course - possibly for cars in GMs UK line.
 
TexasKnucklehead said:
Ordered and will be here in a week. Thanks. I hate driving around wondering if my brake lights are still working!
Click to expand...
Easy check is to watch the ammeter. If it kicks when you step on the pedal, the brake lights are working. At idle or with the engine stopped, you should see it swing farther to discharge and stay there until you release the pedal.
 
Thanks to all for the info and to Geo for the switch info. The TR4 switch I am using has nylon/plastic body and threads which have become stripped, so I, too, ordered the switch from Amazon. Thanks again.
 
TexasKnucklehead said:
Installed the new switch today. It is a much better switch. One issue I had with the other switch involved the physical "load" of the wires. If the side force placed on the lugs changed (because of a wire moving), so did the on/off point of the contacts. The lugs are tight on the new switch and impervious to wire movements. -It actually weighs 10g more tho it's an inch shorter. Thanks for the link/part reference.
Click to expand...

can you show a pic of your TR3 brake switch mounting bracket ( on the pedal)? my hydraulic brake light switch is out.
any specs or tips are appreciated.
 
GTP1960 said:
can you show a pic of your TR3 brake switch mounting bracket...
Click to expand...

One page back Randall showed how he mounted a mechanical switch on his TR3 - looks like a good set-up if I ever go that route:

DSCF0029_crop.jpg


Very stealthy too - someone who have to be very curious (and on their knees with their head in the footwell) to see what you have done.
 
Geo Hahn said:
One page back Randall showed how he mounted a mechanical switch on his TR3 - looks like a good set-up if I ever go that route:

DSCF0029_crop.jpg


Very stealthy too - someone who have to be very curious (and on their knees with their head in the footwell) to see what you have done.
Click to expand...


"
I still use the hydraulic on the TR3 and also use DOT 5 - but I also added a relay to the circuit since I have 5 brake lights instead of the original two."

Geo,

How did you hook up your multi brake lights & relay?
 
GTP1960 said:
...How did you hook up your multi brake lights & relay?
Click to expand...

The relay is on the RH inner wing, above the hydraulic switch. After the switch so the greater load is carried by the relay.

I substituted two-filament sockets in the rear turn signal lamps (used the same sort of sockets as on the front of the TR3) and wired the second filament to the brake lights. Those are LEDs so not a lot more load but they do come on quicker than the incandescent lamps on he corners. Downside is that my rear turn signals may be harder to see when the brake lights are also on - but I do not consider that a big problem.

The 5th brake light is a magnetic base towing light (Harbor Freight) that I set on the rear deck for driving in-town in traffic.
 
Geo Hahn said:
I substituted two-filament sockets in the rear turn signal lamps (used the same sort of sockets as on the front of the TR3) and wired the second filament to the brake lights.
Click to expand...

Was that the bright "filament" or the dim one?

I'm just curious, as I did the same thing with the dim filament as the brake light and didn't especially like the result. That was some time ago, though (on the previous TR3A), so I was still using incandescent bulbs. If I were going to do it again today, I would probably use multiple relays and the original sockets, so the one filament works for both brake and turn.
 
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