Technical Brake lights

[AndrewRL]

Just another plea for help. Back to electrics...

Car passed MOT but they noticed (like I had) that one brake light is fine, the other very dim. At their suggestion I have cleaned up the connections at the rear and bulb holder etc as much as I can but it still remains very dim. Changed the bulb but to no effect (and passed the car anyway).

Presumably current is escaping somewhere. Any other suggestions (easiest first )?

Thanks.

 

[AndrewHarvey]

The rear lights are rather through a brass tag that is compressed onto the top screw holding the light unit in place.
I would recommend removing light unit - clean earth tag and ensure the captive nut in car body is in good order and reconnect. The screw holding the light in place is providing the earth.

 

[stevehg]

As the bulb has been illuminated, it's most likely to be a poor earth connection.

 

[F123C]

I agree with what Andrew Harvey suggests.

A quick way of checking this without dismantling anything would be to connect one end of a length of cable to a known good earth point (e.g. engine casing) and touch the other end to the suspected poor earth point.

In your case above, if touching the cable to the screw holding on the rear lamp results in the light immediately becoming brighter, then you know the earth is suspect and can delve further.

If cleaning the earth doesn't improve things, then you'll need to check out the live feed. If one brake light is working ok, you can assume that the fuse, brake light switch, and most of the wiring is ok. Take a look at the cable and it's terminal at the bulbholder on the faulty light unit. You may find corrosion between the cable and it's terminal which will need to be cleaned or a new terminal crimped/soldered into place.

Al.

 

[AndrewRL]

Thanks all.

Problem solved although a bit embarassing

Spent a long time checking/moving the earth connection, cleaning contacts, replacing connectors all with no success (apart from getting a multitude of combinations of sidelights on/sidelights off/indicators flashing from both bulbs etc etc...amazing what a difference just moving the earth connector can have) :bang:

Put it all back as it was, carefully checking I had the correct connections (a previous Italian owner/mechanic had "helpfully" written on the bulb holder which colour wire should be connected where) and still the same issue

Then I realised that the sidelight when on was very bright on that side of the car but the brake light remained dim and the penny dropped :idea: ...a quick swap over of the two wires feeding the bulb and now all sorted

Lesson learned...think logically, assess all the evidence and do not over rely on apparently helpful hints and clues that may have been left!