Brake light issues

[dudload]

Afternoon all!

Looking for something help and hints on what could be causing a very frustrating issue keeping my car off the road today.

After starting up this morning and, as I haven't driven true car for a few weeks, thought I'd do a walk around to check all lights are working. I quickly noticed that no lights were working at all, checked the fusebox and found both fuses blown. Quickly replaced them and found everything was working except the rear brake lights.

Checked the bulbs and both all ok (strangely enough I had to take the rhs fitting off a month ago as the bullet connector for the rear light had fallen out). I then took both connectors of the brake light switch and electrical taped them together. Stomped on the pedal a few times with confirmation of no lights and went back to the taped connectors - it was very hot and the tape had partially melted. Also when the rear lights are on and my lovely assistant stepped on the brake I noticed that all lights dimmed and the indicators stopped working.

I take it this means I've got a short somewhere in the circuit. Only problem is how to find the bloomin thing? Have tried to check the loom but it's all behind the cloth with no obvious shorts at joins.


Finally, I tried running the hazard lights, which clicked a few times and now also don't work, and the horn now doesn't work too (indicators do still though)

Any thoughts or tips? It's a mobile leccy if I can't fix it fairly quickly unfortunately...

[SteveClem]

Probably worth going round and cleaning/tightening up all connections before spending money on getting an electrician out. Often it's just a dodgy earth or something.

[dudload]

i would have thought that a bad earth wouldn't blow a fuse or cause the join to go hot? i think something has gone wrong given the horn and indicators have packed up too - tested the fuse and it looks ok. ive bought an £18 signal tester that hopefully should help me find if/where the fault is.

Jonathan

[beero]

First of all the lights are not on a fused circuit (I assume you meant the sidelights didn't work) so I don't know why changing fuses cured it. When you took the wires off the brake light switch and taped them together the brake lights should light up without you touching the brake pedal (providing the ignition is on.) This taped connection is likely to heat up if the connectors are a bit corroded, that is, if the lights worked. If you had a short circuit the right hand fuse (white to green wires) should blow.
The horn is on the left fuse (brown to purple wires) and is separate from the brake lights. On this fuse is the interior lights as well, do they work? The hazards should also be on this fuse if wired correctly.
Are you now saying the indicators do or don't work? Also if the lights dimmed this would suggest a poor earthing point. Check your earthing in the boot. In mine there is a connector for all the earths at the boot lock staple on the boot floor. I would also check all the bullet connectors in the boot. Clean the brass bullets with fine abrasive paper and renew any sleeves that are not shiny inside, these are almost impossible to clean if they are corroded.

[dudload]

Hi Beero,

Thanks for the help! Might be easier if I give a blow by blow of what happened and what i looked at:

Started the car up and did a quick walkaround - noticed that the indicators and brake lights weren't working. (Hazards were at this point though)

Checked the fuse box and both fuses were blown - replaced both but no joy on the lights. Now when pressing the brake pedal the tail lights dimmed and the hazards stopped working when brake pedal was on, but returned once pressure released.

At this point i remembered that i fixed the connectors in the RHS rear tail light a few weeks ago as one bullet was loose. Took this apart but all looked ok.

I then took the two connectors of the brake light switch and taped together - walked round to check and lights weren't on. Went back and terminals (they are quite dirty as you said) were very hot and melting the tape. The RHS fuse does have a discolouration in the middle which looks like i caught it just before it melted.

I then went in the boot, removed the spare wheel and had a look for dodgy connections, but i couldn't find any that looked seriously bad. (I did spray dinitrol down the rear chassis a few weeks ago, so checked to see if any had seeped into the bullet connectors, but again all looked clean.)

I then tried the indicators (which still didnt work) and also the horn which didn't work. Chased the loom from back to front and couldn't see anything weird externally.

One very strange thing that happened when i was testing for power (at 9pm in the street!) was when running a multimeter from the body to a terminal on the LHS fuse the indicators started working. I suppose this confirms that the problem (on both sides?) is most likely due to earth points?

[oliver90owner]

If the brake light circuit is drawing current (switch bypassed and joint overheating), either the joint had a high resistance or there is a short to earth. Taped joints are notoriously ineffective and if the fuse did not blow, the circuit was not a dead short. You can connect your meter, if it has a sufficiently high range (careful, or you may blow the meter if not fuse protected!), to check the current while bypassing the brake light switch, both with and without the brake lights connected. Check individual brake lights by connecting a known live feed is another relatively simple operation. It should not be too difficult to isolate the fault.

RAB

[dudload]

If the brake light circuit is drawing current (switch bypassed and joint overheating), either the joint had a high resistance or there is a short to earth. Taped joints are notoriously ineffective and if the fuse did not blow, the circuit was not a dead short. You can connect your meter, if it has a sufficiently high range (careful, or you may blow the meter if not fuse protected!), to check the current while bypassing the brake light switch, both with and without the brake lights connected. Check individual brake lights by connecting a known live feed is another relatively simple operation. It should not be too difficult to isolate the fault.

RAB

thanks Oliver,

just to check (as unfortunately im not too handy with a multimeter) when checking the current when bypassing the brake light switch - should i have the negative on the earth of the car and positive lead on the bridge connection.

[oliver90owner]

The brake light switch is presumably a feed from live to another live (only when the switch is being operated. If that is the case (the usual configuration) the current measurement is made in series with the disconnected wiring. The earth will be the other side of the lights.

RAB

edited to add a g to cnfiuration!

[dudload]

evening all! interesting development - whilst poking around the fuse box with my multimeter the hazards came on and horn also now works. now this is if i push it a bit - pushing (although there's almost no play) can also turn them off.

now - i'm starting to wonder if the fusebox is the issue. i reconnected the two brake light wires after confirming the hazards were working (i know they're on a different side following your advice - but wondering if fusebox is somehow shorting) and still no joy with the brake lights.

however - smoke started to come from the (brand new) 35A fuse on the right hand side and i quickly turned off the ignition. I took the fuse out to have a look and it was brown on top, but hadn't blown. it then started to pour so canned my fiddling around.

any thoughts on whether the fusebox could be the root of all evil in this situation?

Jonathan

[beero]

Quote "One very strange thing that happened when i was testing for power (at 9pm in the street!) was when running a multimeter from the body to a terminal on the LHS fuse the indicators started working. I suppose this confirms that the problem (on both sides?) is most likely due to earth points?"

Yes, very strange!
The fuse box could be a problem. Remove the fuses and disconnect the battery and use some fine wet and dry to clean the fuse holder contacts. The left fuse feeds the horn and interior lights so if the interior lights are okay then the fuse is good. The right fuse feeds everything that operates only when the ignition is on, so indicators, wipers, brake lights, heater etc. So if any or most of these are working then it is not the fuse.
Test EVERYTHING and let us know exactly what is working and what is not and we may be able to track down the problem, but do clean the rear earth points first.

[dudload]

afternoon all

the brakelights are now fixed! i replaced the fusebox, cleaned all the terminals on the fusebox end and the rear light end and everything magically worked!

bit of a weird issue was that the indicators just would not work. i eventually got them working, but had to undo some of the 'work' the electrician did when installing the hazard unit i bought.

per the picture below i disconnected both of the small brown/ white wires at the top of the image that came from the flasher unit, one of which was connected to the old green wire that used to be connected to the "b" terminal on the flasher, and the other was connected to the "b" terminal itself.

bizarrely, the hazards work (even with ignition off as they should) and the indicators work (ignition only) perfectly now, but i do wonder what the purpose of those two wires was? next job is to put proper lucas connectors on the joints he soldered and leccy taped up.

unnamed (1).jpg (74.56 KiB) Viewed 3573 times

(you may notice that there's a flasher unit in the glovebox area too on top of the one in the engine bay i talk about above - apparently he had to install that as the hazard unit going through the current flasher in the engine caused the lights to flash too fast)

[beero]

Glad you got it sorted. Well done

[firedrake1942]

It is worth replacing those bulkhead grommets as without them you will get wear and fraying of the cables - as well as ultimately, more shorting out ! Good to see you have sorted the issue though !