Faulty Brake lights / indica

[sfjsalter]

Hello

This is my first post, so please be gentle. I have recently discovered that the brake lights and indicators do not work on my TR250 (somebody shook their fist at me as I turned left!). I have checked all the bulbs, fuses, and tested the electric supply to the lights, and the switches - no problems with any of that. The hazard warning light circuit and relay is also fine. I am wondering if perhaps it is a problem with the earth, I am not sure of the earth location, but maybe there is some kind of link with the brakes and indicators? Any thoughts on what to check next?

Thanks
Steve

[RogerH]

Hi Steve,

welcome to the forum.

Have you got a decent wiring diagram to follow - http://www.advanceautowire.com/tr2506.pdf

If you have 12V going to the brake lights but they still do not work then that could suggest an earth problem. 

Did you inherit this problem or has it happened suddenly.

 

Roger

[sfjsalter]

Thanks Roger, very helpful and thanks for the diagram.

The unit does have 12v supply when the brake pedal pressed, so yes, it is looking like an earth problem. I will check the rear light unit next, given perhaps linked with brakes and indicators.

This is only a recent problem!

[Rodbr]

What TR are we talking about here?

[sfjsalter]

it's a 250

[Rodbr]

have you physically removed the bulbs from the holders. If not suggest that you do that, clean all contact points on bulbs and holders. Coat the shiny bit with Dyelctric grease and refit. 

Sometimes condensation inside the lens causes a crust to from between the bulb holder and bulb and contacts and bulb contacts.

I think there is a separate earth wire to the light body that also needs to be cleaned.

[sfjsalter]

Thanks - yes I have removed and cleaned all bulb contacts etc, and also the rear light bolt fitting to the bodywork - which I think is earth. I also tested continuity from that bolt to the bulb socket. My next job is to check the rear side lights

[Rodbr]

I would now check the continuity from bulb socket earth part to a wing bolt . It seems very odd that you have checked and found all OK. 

What has changed recently if anything that my have an effect on the lighting.

Re-chroming perhaps, changed rubber gasket, changed screws or bolts. Something has changed but it just needs to be narrowed down.

Do you have the number plate light?

I can't think of anything else you don't appear to have tried.

Just a thought have you actually lit the bulbs  on both filaments and not just checked a filament is visible? If not do this.

Rod.

Edited May 4, 2020 by Rodbr

[Ian Vincent]

Having in the past had all sorts of weird things happen because of earthing problems with indicators and side lights, when I rebuilt my TR3a I connected a separate earth wire from each bulb holder to a proper earthing point in both the boot and the front of the car.  My method for creating an earth point is to remove the paint from around whichever nut or bolt I plan to use and put a lead washer onto the protruding stud/bolt before adding the earthwire followed by another washer and the nut.  I have plenty of lead offcuts from an old roofing project and it stops corrosion happening where I have removed the paint.

Rgds Ian

[tthomson]

One of the problems with testing for voltages is that when using a multimeter, the meter has a very high resistance and may show a perfectly good reading when there is an Ohmic contact at the ground point due to corrosion, paint or dirt. Ian's suggestion above is very pertinent. Make sure there are good ground connections for all lights, whether for brakes, indicators, markers, fog, or any other lighting component. I would go further and say make sure all ground points are really clean and effective throughout the car. Ground problems are nothing but trouble.

Good luck

TT

[RobH]

34 minutes ago, tthomson said:

One of the problems with testing for voltages is that when using a multimeter, the meter has a very high resistance and may show a perfectly good reading when there is an Ohmic contact at the ground point due to corrosion, paint or dirt

A point I have been making for some time.  Far better to use a small light bulb fitted with flying leads for voltage tracing, as that presents a reasonable load and will show up duff connections. 

[tthomson]

I agree with RobH, in that for most situations on a car using a bulb with flying leads is simple and effective option, but need to be fairly low wattage or they can cause their own problems

Multimeters are useful when chasing down more esoteric problems, and for testing out-of-spec devices.

[sfjsalter]

Thanks for the info, I will try those things next. I am getting continuity to earth on both positive and negative sockets of rear side lights, and the rear brake lights (I think, rather than rear lights) - should that be the case? I thought I would only get earth on the negative side. I have replaced the previous little rear offside side light which was slightly blackened but functional, so that is now fine again.

[Rodbr]

If you have continuity to earth on both pos and neg sockets you have a short circuit somewhere that needs investigation.

You should be checking where the bulbs touch the socket to your earth point for continuity. There are no positive and negative sockets that I know of. The bulbs earth through the pins in the shiny bit. The female receptacle  has slots with a 90 degree lock section that the bulb earths through. Make sure that the contact pins or springs which are your power supplies for side and indicator are not bent a touching to earth under compression.

Rod

[Lebro]

Have you taken all the bulbs out ? if not you will get continuity at the bulb contacts (although not "short circuit) through the other bulbs filaments.

Bob.