Brake lights not working.

[Ian21401]

Agreed, it doesn’t make sense.
There must be 12v in one of the wires to light the brake light filament. If that wire is switched with the tail light wire the tail light should be lit. That’s assuming that you have twin filament bulbs fitted correctly.

[PurpleTurbo]

Originally Posted by Laird Scooby

That doesn't make sense if they are normal bulbs unless a filament is blwon. Do you have a multimeter?

I do yes

[Laird Scooby]

Originally Posted by PurpleTurbo

I do yes

Whip the bulbs out, set your meter on the 0-200 resistance range, hold one probe on the metal body of the bulb and then touch the other probe to each of the terminals on the base of the bulb in turn.

One should give ~25 Ohms, the other should give ~6.7 Ohms (this is the 21W filament i.e. brake light) then repeat for the other bulb.

I suspect one or other of the filaments in both bulbs is defective.

Once you've proved the bulbs are dead or alive, fit working bulbs to the bulbholder and after you've located the common earth terminal (it's the one that mates with the long strip on the back of the cluster running top to bottom) connect one probe to that and then touch the other two terminals in turn, looking again for the same readings as the bare bulb.

[PurpleTurbo]

Originally Posted by Laird Scooby

Whip the bulbs out, set your meter on the 0-200 resistance range, hold one probe on the metal body of the bulb and then touch the other probe to each of the terminals on the base of the bulb in turn.

One should give ~25 Ohms, the other should give ~6.7 Ohms (this is the 21W filament i.e. brake light) then repeat for the other bulb.

I suspect one or other of the filaments in both bulbs is defective.

Once you've proved the bulbs are dead or alive, fit working bulbs to the bulbholder and after you've located the common earth terminal (it's the one that mates with the long strip on the back of the cluster running top to bottom) connect one probe to that and then touch the other two terminals in turn, looking again for the same readings as the bare bulb.

Ive fixed it! Thanks everyone for the help.
The bulbs were not giving out the ohms you stated but they are 21W bulbs.

Turns out that at some point the contact point on the light assembly had been pushed into the housing so the contacts weren't meeting.
Cant wait for something else to go wrong next week!

[Laird Scooby]

Originally Posted by PurpleTurbo

Ive fixed it! Thanks everyone for the help.
The bulbs were not giving out the ohms you stated but they are 21W bulbs.

Turns out that at some point the contact point on the light assembly had been pushed into the housing so the contacts weren't meeting.
Cant wait for something else to go wrong next week!

Either something wrong with the multimeter or your measurement technique then!

Volts/resistance = Current, Voltage x Current = Power (W)

12/25 = 0.48A , 12 x 0.48 = 5.76W

The ~25 Ohms was a guesstimate but as you can see, pretty close!

12/6.7= 1.79A , 12 x 1.79 = 21.49W

Again, the ~6-7 Ohms was a guesstimate but as you can see, close enough in both cases to be correct for the 21/5W bulb you should have.

Glad you've sorted it and hopefully learned that sometimes a problem is simpler than you think. Very often with these cars the problem is so simple it's staring you in the face but people are conditioned these days to look for the complicated solutions.

In this case, some muppet had tried fitting the bulb the wrong way in the socket and pushed the contacts too far in so with the bulb correctly fitted, it wasn't making contact and working.

[MiniNinjaRob]

I have to say I had an issue with my brake lights and it was the plastic bit that had broken so I bought some new tail lights.

The second time I had an issue I had bought the wrong bulbs and could not for the life of me figure out what I had done wrong. I think I compared them to the old ones and realised but I felt like such a dimwit.