T3 Rear Brake Stop Light Switch No Work

Stop light has ceased to come on when rear linked brake is pressed. Front works fine. Assuming the pressure switch has packed in does anyone know if you have to first drain the system of hydraulic fluid to fit a new one? Thanks for any help.

My rear brake light switch wasn’t working when I got the T3. Turned out to be a bad electrical connection. Fortunately I checked that before I removed the pressure switch (which was my first instinct). Could be worth eliminating first.


If you do need to change the pressure switch, I don’t think you need to drain the system first (as long as you’re quick), but you may need to bleed the system afterwards, which is allegedly a PITA.

one brake light (either front or back) is all that is required for an MOT, if you are happy with one just disconnect the wire to the rear switch. If it is fitted and does not work that is then an MOT failure

I would follow the above advice,you do not need to drain the system but put a rag around the area of the switch. the wires to the rear lights/turn signals should be connected via a 4 wire connector running along the top frame tube behind the right hand side panel, but as T3’s are now at least 35 years old the wiring could have been changed over the yearsthink Intermotor Brake Light Switch no 51650 works on T3’s, just take the old one to the local car spares place, Volkswagen Beetle unit from the 1970’s.if you have braided brake hoses the job of bleding the brakes after the new switch is fitted should not be too hard a job, but if the original brake hose is still fitted well yes it couls be a pain in the wotsits to do.

northwest2014-06-24 18:02:09

Try shorting the electrical cable to the frame to see if the brake light comes on.
That should show if it is the pressure switch that is faulty or not.
I have to say that I have not found bleeding the brakes to be a big issue. As many Cali riders use the linked brakes the front does not get as much use as on most bikes so it is probably best to get the system sorted or you might have a passed MoT but a bike that is not giving following drivers a bit of useful data!CylvaBirch2014-06-24 18:44:43

This is true up to aqbout 1986 bikes. After that both must work.As the rear Linked system is the one you would use most then I suggest that needs to work.As pointed out above very easy to fault find on and sort.

Don’t short the wires to the frame, touch the two wires together to test it. Touch to the frame and you are going to blow the fuse!The switch unit is located on the back of the splitter unit on the left side, just in front of the top shock mounting. You should see 2 wires connected to it Try that first. If it makes the light come on then the switch is dud.

Due to its location it is just as easy that the connectors are caked with mud and corrosion, there’s supposed to be like a rubber bootee over it to try keep out the worst. I also have normal 1/4" covers over the female blade connectors as well.

Thanks everyone. It was the connectors. Having just put new brake lines on it and still a pain to bleed with the old 2 nipple calipers I didn’t really want to repeat the operation.

Excellent. There ya go check the simple things first.