Suddenly, no brake lights! where do I go from here...

[ron88]

All other indicators work, headlights, etc. Just had someone tell me (two actually) that my car is running without brake lights. Very sudden. I haven't begun to check anything, but I was hoping for some guidance as the best place to start. Would that it would be so simple as a fuse (fingers crossed). I am terrible at Lucas electrics, hence the naive starter question.

[ianc]

On a standard TR4, one fuse feeds:

- Fuel & Temperature Gauges

- Wipers

- Heater Fan

- Brake Lights.

 

If most of those are operating, it will the fault will lie with the brake light switch, of which there are 2 types:

- a pressure switch mounted in the 5-way junction in the brake line below the master cylinder

- a switch mounted on top of the pedal assembly such that as the piston is pushed into the master cylinder, the switch is operated.

 

If the latter, a superior type of switch is available - search the Forum for details (I think it may be from some German car manufacturer).

 

Pressure switches can fail - if you're quick, you can replace a switch without much loss of brake fluid (a.k.a. paint stripper, so be careful) and the need to bleed the brakes!

 

Ian Cornish

[RogerH]

Hi Ron,

check for 12V on the live side of the brake switch.

Operate the switch and check for 12V

In the boot area the single wire coming from the brake switch splits into two - Check for 12v.

 

You could simply put 12V on the lamp side of the brake switch and see what happens.

 

Roger

[TR 2100]

Failure of the pressure switch is a favourite, especially if you

have a 4-branch.

Try really standing on the brakes (when you are stationary!)

and see if they come on. Not guaranteed and not conclusive,

but easy to check.

 

Ah but - (see below) - my post relates to the earlier models

with a switch fitted in the hydraulic circuit. Later models (4A)

had a switch on the master cylinder bracket.

 

Thanks, Stuart (again!)

 

AlanR

Edited July 16, 2013 by TR 2100

[peter clarke]

Check for power to switch by connecting 12 volt bulb between earth and each wire in turn with ignition on. (one wire lights bulb = power supply ok)

Check switch.....remove both wires and join together (care not to earth out) ...turn on ignition and check for brake lights.(lights = faulty switch) no lights = faulty connection in harness between switch and brake lights

[cvtrian]

and don't forget to check the bulbs are OK................

[ron88]

Thanks will give it a go....is the pressure switch on the pedal an electric or does it screw into the brake line? I've got a 66 4A. Or, in the engine well near the master cylinder?

[stuart]

It should be on the front of the master cylinder mounting bracket. Check that you have voltage up to it and that its not seized up/button stuck in. The original metal Lucas ones were pretty long lasting as opposed to the new plastic Lucas ones which are very poor.

If you do need to replace it then these are better. http://www.ebay.co.uk/itm/Facet-Brake-Light-Switch-BMW-7-E23-735-i-77-86-/360690200167?pt=UK_CarsParts_Vehicles_CarParts_SM&fits=Car+Make%3ABMW&hash=item53facfae67

Stuart.

Edited July 16, 2013 by stuart

[ron88]

Thanks Stuart - just checked but the website says not compatible with a TR4A 66?

 

Will go over the car tomorrow. Manufacture was Dec 65

[peejay4A]

It will fit. If you find one that says it's for a 4a you'll likely finish up with the useless nylon thing that will last 5 minutes.

[stuart]

I fit them regularly so ignore what it says there. Its originally for a 7 series BMW but it works fine and keeps on working unlike the **** plastic ones.

Stuart.

[ron88]

Ok, good news then. I'll get to the car and check it all out.

[Badfrog]

One seldom thinks about the bullet connector in the stop light line. It's the one under the dashboard, at the top of the lateral panel (driver side in a LHD). That was my last "no lights" trick and took me days to figure it out. Everything else was fine.

Undo the connector, sand the contacts, put them back in and voila ....

 

Badfrog

[ron88]

 

Where do the other electrical wires go to? I understand two, but not four......

[peejay4A]

The Green is the ignition switched live feed from the fuse box. The Green/Purple feeds the brake lights. The others are not standard and it looks like a previous owner has used the Green as a source of ignition switched power for something. On a standard loom only the Green and Green/Purple should be present.

[ron88]

Hi stuart, it's definitely the switch as I joined the wires and the lights came on. I ordered the one you suggested and installed it - but the brake lights stayed on! No amount of fiddling could make it work. Wonder what I did wrong - swapped wires, made sure it was not depressed, etc...bit of a mystery

[peejay4A]

Ron. Sorry if this sounds obvious but the switch operates when the pedal lever moves away from the plunger. So if you depress the plunger the lights should go out.

[ron88]

No I appreciate the observation. That said, I did remove the switch, connect the wires (which turned on the lights) and then fully depressed the plunger. Lights stayed on

[peejay4A]

Sounds as though you have a dud switch. Can you check it with a multimeter?

[ron88]

Ok, I'm the idiot. I had not depressed the plunger far enough on the new switch. Thought I did. Once reconnected and up against the pedal lever very tight, it works. I had left too much slack previously. Problem solved. PS No idea what the extra gray wire does (or did) but may find that out down the road!

Edited July 26, 2013 by ron88

[peejay4A]

Good news. Get out there!