Brake light electrical issue

OatMilkMan · Jan 18, 2021

Hi there,
My brake lights stop working the other day and I went under to see what the issue was. There was a number of corroded wires underneath (at rear right of car). A previous owner had installed a plug for a trailer but these had all corroded so I cut them back and reconnected (albeit just to test) the same coloured wires but the brake lights still didn't work. I checked my Haynes but couldn't see much on it.

Please see the picture but there was also an earth wire which was loose and I wondered if that could be part of the issue?

Any advice would be really appreciated and I also appreciate it might be a simple fix I'm just still learning my electrics!

Thank you,

Scott

lynall · Jan 18, 2021

Start with brake light switch and the power supply to the switch, then work your way back from there.
A mulitmeter is nice, but a bulb and two wires will do the same thing on simple circuits like you are looking at.

layfin · Jan 18, 2021

Bad earth causes all sorts of wierd and curious problems.

TheMegaMan · Jan 18, 2021

layfin said:
Bad earth causes all sorts of wierd and curious problems.

So, so true. Get the earth attached properly, and try again.

That wiring looks horrible, however. Were the wired just twisted together? In the wheel arch? That's never going to last. My trailer socket was wired in using chocolate block, which I thought was bad enough, but at least it was up behind the cover inside the body of the tub, out of the spray from the road. Done it properly with bullet connectors, now...still protected from the wet.

OatMilkMan · Jan 18, 2021

lynall said:
Start with brake light switch and the power supply to the switch, then work your way back from there.
A mulitmeter is nice, but a bulb and two wires will do the same thing on simple circuits like you are looking at.

Thanks for the advice, I went and got a multimeter and followed the wire, do you know where it goes after it goes behind the dash?

Thanks again!

OatMilkMan · Jan 18, 2021

layfin said:
Bad earth causes all sorts of wierd and curious problems.

Thanks for the advice! Maybe it is the earth, I don't know it you can see in the photo there was an earth which I think was for the trailer, but maybe I somehow need to reconnect it

OatMilkMan · Jan 18, 2021

TheMegaMan said:
So, so true. Get the earth attached properly, and try again.

That wiring looks horrible, however. Were the wired just twisted together? In the wheel arch? That's never going to last. My trailer socket was wired in using chocolate block, which I thought was bad enough, but at least it was up behind the cover inside the body of the tub, out of the spray from the road. Done it properly with bullet connectors, now...still protected from the wet.

Thanks Mega,
No that was just me that twisted them to test after cutting away the corroded trailer wire. Would I need to connect the earth up to four wires you see there?

They do go into the back of the rear lights and they are earthed there.

TheMegaMan · Jan 18, 2021

OatMilkMan said:
Thanks Mega,
No that was just me that twisted them to test after cutting away the corroded trailer wire. Would I need to connect the earth up to four wires you see there?

They do go into the back of the rear lights and they are earthed there.

OK, that's not quite so bad, but you really want to avoid having connectors where they will get wet and muddy, so would be better taking the wires up through the top of the wheel arch (through grommeted holes, of course) and connecting everything up in there. But you may not have a lot of choice.

I'm not actually sure I can make out 4 black earth wires on those photos! But really, connect all earths as often and as well as you can. My tail lights have 3 wires - tail, brake and earth. The lights may well earth to the chassis when they are screwed on, but I make no assumptions and earthed the black wires from the lights and loom to the chassis, too. You really can't do too much!

TheMegaMan · Jan 18, 2021

OatMilkMan said:
Would I need to connect the earth up to four wires you see there?

Sorry. I've looked again, and I don't see 4 black wires...actually, I'm not sure I see any black wires at all. Which are the ones you think are earth?

TheMegaMan · Jan 18, 2021

Just a thought...you're not assuming all the green striped wires need to go to earth, are you? Black is earth on a Landy... The green wires will be the indicator and stop light 12V supplies, and you really don't want to be earthing those, and you'll short out the lights, and blow a fuse if you're lucky...melt a wire or switch if you're not.

Sorry if that's not what you mean and know they aren't earths, but it just got me worried when you referred to 4 of them, and I can only see 4 sets of green wires.

lynall · Jan 19, 2021

OatMilkMan said:
Thanks for the advice, I went and got a multimeter and followed the wire, do you know where it goes after it goes behind the dash?

Thanks again!

Sorry no idea, but we are pretty simple here, so guess ign live feeds the brake light switch, have you checked there is power at the switch with ign on? if so then press switch and see if power is making it through the switch? if so then (and I am guessing here) it will come from switch into chassis drivers side, then emerge chassis drivers side at the rear to a connector that will split it so it can feed both brake lights.

If you google land rover series wiring diagram, pick which model 1/2/3 is yours and have a go at following the colours.
They are simple, but can also be bloody annoying as well!

Checking for power is a piece of psis, checking for a decent earth is slightly harder, so always worth running a temprorary length of wire back to the battery negative so you can confirm any fitted earths are any good.
The fact you are having a go means you will fix it, it may take some time but when you suss it you will be proper chuffed.

OatMilkMan · Jan 22, 2021

Thanks Mega and Lynall! So I removed the wiring for the trailer plug, reconnected the wires, fitted new LED bulbs and it worked

I am proper chuffed - thanks for all your help!

lynall · Jan 22, 2021

OatMilkMan said:
Thanks Mega and Lynall! So I removed the wiring for the trailer plug, reconnected the wires, fitted new LED bulbs and it worked I am proper chuffed - thanks for all your help!

Good result, builds confidence as well as there will be other electrical issues, people blame the cars but in reality it is normally the previous owners bodges/repairs gone wrong.

Always worth carrying a few feet of wire, insulation tape, chocky blocks, few basic hand tools, with that you can pretty much fix any elec issue on them.
I have run a wire from battery to haadlights as floor mounted switch went wrong 100 miles from home.

OatMilkMan · Jan 22, 2021

lynall said:
Good result, builds confidence as well as there will be other electrical issues, people blame the cars but in reality it is normally the previous owners bodges/repairs gone wrong.

Always worth carrying a few feet of wire, insulation tape, chocky blocks, few basic hand tools, with that you can pretty much fix any elec issue on them.
I have run a wire from battery to haadlights as floor mounted switch went wrong 100 miles from home.

Great advice, I will do exactly that

Thanks again for all the help!

Brake light electrical issue

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