Earthing Problem - Fault Finding

[Jaye R]

Having driven home from Chatsworth with my car lighting up like a nightclub each time I braked or indicated right I am going to be fault finding this weekend - I presume it is an earthing problem somewhere.

Any tips on where to start looking??

It happens when braking (front headlights light up), engaging reverse (again, front headlights light up) & indicating right (front headlights flash in time with the indicator).

Thanks in advance.

Cheers
Jaye

[SS2.]

The first place I might be inclined to start looking would be the [infamous] rear light clusters.

[Last S4]

Hi,
If you connect a long cable directly to the battery earth then you could use this to fault find. Just connect the other end to the earth on each cluster etc one at a time - if the fault goes you know where to start tracing from.
Steve.

[Barkychoc]

On my car (battery in the boot) the main earths from the chassis to the wiring loom are behind both front wheels, just where all the crud off the wheels can blast them.

Obviously also check the battery earth to chassis (as I'm a V8 I don't know where this is on yours, but it can't be hard to find) and there should also be a substantial earth from the engine to chassis.

Don't just check they are tight - take them off and clean them up.
Some petroleum jelly on reassembly or something similar will help keep the moisture out.

Also as has been said check the light clusters themselves too.

Edited by Barkychoc on Wednesday 29th April 09:39

[ketvrin]

Hi Jaye

all faults you state would involve the offside rear light cluster so thats got to be the first place to start...

good luck

K

[Jaye R]

Thanks for your help guys - will be having a look at the weekend, so hopefully will all be sorted for SCH09 - roll on June

Cheers
Jaye

[spludge]

I would clean up the chassis earth points before trying anything else, they can get pretty mucky over time. There's four on the S3, one on the front crossmember takes the earth strap from the battery, take that off and leave it off until the rest are done. One each side on the chassis diagonals just in front of the bulkhead and one under the n/s wheelarch.

I had a bent pin on a rear light connector and corroded contacts on the multiway connectors that feed the front lights which both caused problems similar to those you describe.

K

[bil]

there is also an earth strap between the gearbox and the chassis at the mid rail/gearbox mount.... well there is on mine...

bil

[jimed]

Cleaning up the earth points does sound like a good idea but I'm puzzled by spludge's comment that the battery earth lead should be disconnected when the others are being cleaned. Is there a reason for this or if I were to take them off and clean them and then re-attach one by one would there be a problem? My thought is to put a jumplead across from the battery to earth somewhere so as to maintain ECU settings (not starting it like this though!) and work through them. Any comments??
Jim

[Wiz]

If your messing with the electrics I'd disconect the battery, just to be on the safe side. As well as the earth points I'd check the connector blocks as well and give them a clean with connector/carb cleaner. Sure the ecu is ok if the battery is disconected for a short while. Don't quote me on that!

[spludge]

Safety and comfort. Its all to easy to short something when you are messing about with electrics, disconnecting the battery eliminates that problem. Reconnecting the battery on mine arms the alarm, having that thing go off in your ear a few times when you are working ain't nice!

Tvrgit posted something on ECUs a while back, IIRC it needs a full temperature cycle of the engine, till the radiator fan cuts in, to re-learn its settings after a disconnect.

K

[Jaye R]

Thanks for all the advise guys - turned out to be a 30 second job (thank god as I was rather fragile after a 'good' Saturday night out).

The connector had come loose in the off-side rear light cluster - probably due to the rattling it got on the run over to Chatsworth - the road surfaces weren't that fantastic shall we say.

Thanks again.

Cheers
Jaye

[jimed]

I've just gone over post this again as I was told after the run on Sunday (side lights on in the rain) by the bloke in the Sag who was behind me (he didn't manage to get past - OK I know ...) that the side lights at the back were winking when the indicator was on - ie bad earth. I checked them when I got home and they weren't too bad at all in fact I had to look reasonably closely to find it; anyway I had a look again this am - the near side is fine but the off side does wink slightly but not as a major issue but worth correcting. I've taken the bulb holder off and checked the connector and all seems fine but I cleaned the earth pin anyway - no change. The only point I would wonder about in what I've looked at so far is the actual connection to the indicator bulb where the earth bit of the socket seems to be not very proud at all from the plastic bulb holder. I tried to get a small knife in to ease it out a little but failed so would that cause my problem/has anyone any experience of that as a problem and maybe managed to tweek the earth connection out a bit? Next thing to check is probably the earth at the back (I did the main earth when this was originally posted and it was fine but cleaner now) but I'm puzzled as the n/s are OK so it suggests the rear light off side cluster itself may be the problem - maybe I'm making a wrong assumption here so any advice/thoughts appreciated.
Jim

[Barkychoc]

Jim - try it with the brake lights on (you need a friend!) you may find its worse then.

[jimed]

I've not tried it Chris but as you say it'll be owrse I'm sure - hadn't thought about that ... any ideas what is the likely problem anyone (I'll have a look at the rear earth anyway in the next few days) - later (edit) I wonder if the actual connections to the eye end (ie the wire into the eye end) gets corroded like the front light connections round the bonnet were on my car before I replaced them. If so I will need to get some new eye ends I can crimp then solder on in case so has anyone any experience of this as a problem?
Jim

Edited by jimed on Wednesday 29th July 10:19

[jimed]

Thought I'd give an update of the rear lights issue - jacked the car up this am and found the earth on the cross member at the n/s top front of the fuel tank - easy access with the wheel off. The rear light earths are both into one terminal and it was clean with no sign of any corrosion and the copper from the wires still looked shiny so all being well it is OK although next time I will take it off and solder on a better terminal as the current one looks like alloy of some kind and not solder friendly. The other earth there is from the fuel tank.
Whilst it all looked reasonably good the whole arrangement was a bit naff; the earth is a stud from the chassis member on which were 2 over size nuts pushed up against the chassis which was painted (as was that bit of the stud) so little contact. Against that was an oversize washer then the 2 terminals then another oversize washer and finally the correct nut. Clearly it has been working for 18 years so far but not the best I thought so after cleaning it all up I put on the 2 large nuts followed by a clean correct size nut which was then tightened. Against that I then put a small washer then the fuel tank terminal then a large washer and finally the rear lights earth, a correct size lock washer and the correct clean nut.
I then checked the lights and with the indicator on the offside rear light did wink ever so slightly (had to look carefully though and it may be a bit of a mirage with the indicator being next to it and much brighter when it winks, thus making the rear light look to dim slightly?) as they did before but then tried the brakes and all was fine with no wink effect at all. As I'd assumed the lights would be worse with the brake lights on I didn't try it before so don't know if its any better but it is certainly better earthed than it was before and works fine so that's it. It is strange though that there is a slight wink at one side without the brake lights so maybe I'll have a look at the connectors again some time; any ideas re that appreciated - I suspect its in the rear o/s cluster somewhere but not sure what??

Jim

Edited by jimed on Monday 3rd August 17:04

[ketvrin]

Could it be a problem with the indicator switch on the steering Column Jim ? maybe theres some tracking across the circuits going on there...

with the lights off, and the indicators flashing, can you pick up any readings from the light circuit each time theres a flash ?

I hate electrical problems

K

[johnnywgk]

BUMP!

Just wondered if all was OK now, i got a bit of a christmas tree affect
at the moment, will try all above later, was there anything else you did.

Cheers