Hi all

I have been working on this MOT forever its on a 1978 S3 2.5ltr Diesel. Drove it back from the MOT centre and as i was pulling on the drive it stalled and sparks ahoy, the earth on the gearbox under the center seat was sparking and then burnt through.

Took it off as it gose from the earth of the battery to the gearbox, now when i take a lead from the battery and put it on any metal part of the car i get a shed loads of sparks.......
Anyone know why?

Are you sure that you're using the -ive terminal for earth? (Seen the opposite done!)

If you are, then you have a major short for it to burn out the earth strap. I'd be looking at the +ive leads from the battery, starter & alternator as these are direct to the battery, so there is no fuse protection (which would have blown otherwise)

Presumably you mean you're getting sparks when you try to connect the earth lead to the bodywork - connecting the live would certainly result in sparks!
Does sound like the live has shorted to the chassis or engine, and at a fairly high current - follow the starter motor cable from the battery to the starter and see if the insulation has chafed or burnt through.

Disconnect the thick wire on the starter that comes from the battery and tape it up temporarily, then unplug the connector off the alty.
Quickly 'flash' the battery connection to earth again, if theres still a boat load of sparks then theres a wire rubbed through (unlikely but could also be a fault around the fusebox or dash area), if theres no sparks, disconnect the battery again then plug in the alty and try again, if theres sparks when you flash the battery then the alty is dead, if not then try again with the starter re-connected, if theres sparks when you flash the battery again then the starter is dead.
More likely by the sound of it that the battery positive cable has worn through somewhere.
Edit: instead of 'flashing' the neg lead onto the battery, connect a jump lead to it, and flash the other end to the chassis away from the battery, theres a risk of explosion if you create loads of sparks around a battery.

to ask the obvious question... it is a negative earth vehicle isn't it?

found it...

The battery is located in the well under the passanger, traced the main cable from the + into the engine well, the cable was lose and rubbing against the exhaust. The heat has melted the cable coating...

Just to say i didnt put the cable there and will be running it differently tomorrow.

Side-show-bob said:

found it...

The battery is located in the well under the passanger, traced the main cable from the + into the engine well, the cable was lose and rubbing against the exhaust. The heat has melted the cable coating...

Just to say i didnt put the cable there and will be running it differently tomorrow.

Click to expand...

Another success for landyzone! Don't forget to replace the burnt out earth strap.