[Mk2] [Generic] Dash lights dimming when braking

[jonb-]

Hey all,

Odd problem. When I brake my dash lights dim. My little turbo timer with a voltage read out can dip as low as 10v if my charge cooler pump, headlights and windscreen wipers are on (it's a bit like if you pull up both electric windows when they're already up, that sort of power drain.)

Now instant assumption is the alternator is dying but the rest of the car functions as normal, and if i turn everything off I get the 13.x on the turbo timer.

Any one any suggestions? The chargecooler pump is wired into the fog light circuit and hasn't been a problem before.

I did start blowing a fuse a few years ago after me and nightspirit installed a push to start button (yet only about 800 miles ago ) that cut all power, so i just replaced it with a bigger fuse. I guess I should check which fuse it was

I'm rambling now. I hope everyone is well

[black gts]

it might be a short on the rear lights,(bad earth?), get some one to press the brake pedal for you , with lights on and off , fog light aswell just incsae

[Si_Crewe]

Having all the lights go dim when you do summat like apply the brake lights is very often a sign of a bad earth somewhere.

FWIW, your brake lights don't draw a great deal of juice.
Each one is 20w which means they draw about 4 amps altogether.

Do you get the same problem when you put your headlights on, or your front foglights, or your a/c?

If you DO then the problem probably IS a charging fault but, in that case, your charge warning light should also come on to warn you that your car isn't making leccy fast enough.

If you can switch the headlights on (which draw more than double the current) without causing problems the problem is almost certainly a bad earth or a short-circuit somewhere on the braking circuit.

[jonb-]

Thanks guys, that makes sense.

Now I get to go earth hunting! We did a bit of rewiring under the dash as the chargecooler pump is on the fog light circuit so perhaps we messed something up under there.

I suspect it might be a tricky one to find

[Si_Crewe]

Well, much as you probably don't want to, your best bet is probably to start by undoing what you did.

Did the fault start happening IMMEDIATELY after you did your tinkering or is it just summat that's started now, after you did some rewiring a couple of months ago?

If it's the latter the fault could be totally unrelated.
It's winter and the roads are covered in salt and salt can seriously mess with car electrics.

An afternoon attacking your leccy connections with a wire brush and a jar of vaseline may be all that's required.

[jonb-]

Well, much as you probably don't want to, your best bet is probably to start by undoing what you did.

Did the fault start happening IMMEDIATELY after you did your tinkering or is it just summat that's started now, after you did some rewiring a couple of months ago?

If it's the latter the fault could be totally unrelated.
It's winter and the roads are covered in salt and salt can seriously mess with car electrics.

An afternoon attacking your leccy connections with a wire brush and a jar of vaseline may be all that's required.

My car is special. I actually did the wiring a few years ago but it's only covered a few hundred miles in that time. TBH I can't even remember what we did or how bad the problem was before.

Perhaps I'll take it to an auto electrician and play innocent I'll have ago at checking all the major earths first.