Electrical weirdness (Sorted)

Post by **v-lux** » 06 Sep 2007, 13:27

Hi,

Van seems to be blowing brake light fuses like they are going out of fashion.

Also noticed the other day, just after replacing the said fuse i was testing the brake lights to make sure they came on.

But, well, they did come on but very dimly, and they made all the rest of the lights on the van go weaker.
Headlights, rearlights, interior lights, dash lights etc etc.

Ironically it started doing this after i had the entire electrical system checked out and a new battery installed whilst in Portugal.
(I had it checked more to put my mind at rest as we had been suffering with some buzzer of doom, so was just making sure the senders etc were doing their thing, along with an oil pressure check)

Anyone got any ideas.

Website · Post by **syncrosimon** » 06 Sep 2007, 14:29

Usually when a brake light or similar is put on and it makes the surrounding lights go dimmer it is an earth problem. All the lights in that cluster have to get their negative voltage through a defective earth which makes the whole lot go dim as there is less power to share around. That problem though should not blow the fuse. Only a short out would normally blow a fuse in my experience.
try unplugging the rear light clusters one at a time and see if the situation improves. Check the new battery is giving out around 13 or so volts when the engine is running, a defective alternator can send the volts too high which may blow a fuse, but would make the lights brighter.
good luck
electrics is the worst.
simon.

Post by **v-lux** » 06 Sep 2007, 15:26

Getting 13v from the battery when running, so im guessing that's probably ok

Im wondering if all of this could stem back as far as my gearbox change? The fuel gauge decided to pack in just after i had changed the box.
But i'm pretty sure that i didn't mess with any electrics on the van during that time. Other than the gearbox earth of course. (could be worth checking again i guess, make sure its actually making a good contact)

I have noticed that the drivers side rear light keeps going out every now and then, a quick bash with a fist usually springs it back into life, could this be contributing towards the fuse blowing?

Website · Post by **syncrosimon** » 06 Sep 2007, 15:47

I wonder if the main wiring harness has been squashed, that would account for all the weirdness. I think it runs over the top of the gearbox somwhere. would have needed a really good squeeze to break the insulation though. If a bang on the rear light cluster sorts it, then it's likley the problem is in that cluster. unplug the cluster and check the voltage getting to the rear lights. check the continuity on the earth connections. see if the voltage drops as you switch on more lights.

Post by **v-lux** » 06 Sep 2007, 16:27

Nice one, will do!

Many thanks

Post by **garyd** » 06 Sep 2007, 19:44

Dim lights and blown fuses sound like two different problems.

As has been said, a bad earth at the lamp unit will cause dim lights and often make both the tail lights come on dimmly when the brakes are applied. (The power applied to the brake filament cannot earth directly so goes back through the tail-light filament, through the loom to the other tail-light and then earths from there.) If anything, this will reduce the current being drawn by the brake light circuit.

A repeated blown fuse can only be caused by high current. Can you get an ammeter on the feed from the brake light switch (I am guessing that this is above the pedal). If it is only feeding two 21 watt bulbs it should show about 3.5 amps. If you are blowing 10amp (?) fuses, it might show in excess of that. A partial short to earth seems most likely.

The suggestion of a crush cable during the gearbox work sounds a good possibility. I don't know off-hand where it runs but follow it back from the rear lights and see what you find.

Good Luck.
Garyd

Post by **v-lux** » 06 Sep 2007, 21:30

Something i remembered earlier..!

Ive been installing a new interior recently and as such have had to mess about with the rear interior light.
(its the only electrical thing i can think of that iv'e meddled with over the gearbox install period)
When the van was all back together and i started fettling any oddities, i discovered that the interior lights were not operating with the door switches. Whether this was coincidence or not, i remember finding that the brake light fuse was blown and replacing it seemed to make the interior lights work properly again? (is this possible, or was it a coincidence?)

Anyway, ive had a fiddle with the interior light, made sure that the contacts are good, added a bit of insulation tape to parts that could be making contact where they shouldn't and it seems to have sorted it.

New 10A fuse installed, all lights tested and working correctly, no dimming of other lights when the pedal is depressed.

I still need to check the rear light cluster, theres obviously some contacts that need a fettle in there, but for time being it seems ok.

Does this just sound absurd? or is it possible that the interior lights could be having some effect?

Post by **garyd** » 07 Sep 2007, 16:52

Accordinging to the info I have for 1989 on diesel Transporter the brake lights are on fuse 2 and the interior lights on fuse 3. Both should be 15 amp rating.

Can't immediately see why one should affect the other unless everything off the fuse box busbar was also affected (but not noticed?)

cheers
Garyd

Post by **v-lux** » 07 Sep 2007, 19:25

As it happens, ive blown the fuse again. So they cant have been related.

Hmmm, this is a bit outside the realms of my understanding.
Anyone know a good auto electrician near Exeter?

Ive got MOT coming up at the end of the month......

Post by **v-lux** » 21 Sep 2007, 12:02

All sorted.

Turns out the Towbar electrics were at fault.
One of the mounting screws for the socket under the bumper had pierced the cable going into the socket.

Resulting in the short circuit. Caught it just in time too it would seem, as it was just about to start affecting the sidelights too.

Should anyone need a good auto electrician near Exeter, who just happens to be VW friendly too, then John Harrop is your man!
Superb service, quick as you like.

Send me a PM if you need his number.

Post by **Louey** » 21 Sep 2007, 15:15

I'm wondering if you might have given me the answer to my problem - the indicators stay on instead of flashing when I put my foot on the brakes, I had my towbar electrics hit by a motorbike and It might have knocked them about a bit

if not, mines an earth problem