Dodgy wiring HELP

[cynic-al]

Loving your input Ron - the foot switch is kind of loose, as the original mountings seem to have gone and it is attached by a metal tab* (1 of 2 - the other has disconnected). No other wires under the dash (bar the brown) look melted.

*I suspect that there is an issue with this fitting method that may have caused the short. I'll get the ohm-meter out tomorrow. If you're right I may post you a pint of Guiness, but you should really try some proper beer:

http://www.caledonian-brewery.co.uk/

[Derek UK]

Ron's doing very well here. The switch should be screwed straight to the floor. There is a small pressed island for it. Maybe one of these metal tabs has shorted out to the powered centre tag. As the switch is screwed to the body it is essentially an earth. What does the tab do?

[cynic-al]

Only just got to looking at this again. I've taken the footswitch out. It seems to be lacking any form of backing that would stop the connectors shorting against the body - this can't be right, can it?

It seems that the blue wire must have shorted against the footwell, as the switch was loosely attached and moving around. I am thinking if I can secure it and put some insulation in that should sort the fault.

Here's a pic.

[Ron Kwas]

Al;

...a most interesting finding...but it certainly proves you're on the right track...apparently, someone planted a time bomb for you...clearly the switch was taken apart and the bottom was not put back on...very peculiar!!!

...to details: If the Blue wire was the only heat damaged wire, that pretty much proves that the short occurred (and thankfully was limited to!) at the switch. A short in this manner also (probably) did not damage the switch (but why it was taken apart in the first place is still not answered). I would tkae the switch apart totally if you can to inspect internals, and if you don't find anything which would make you need to replace the entire switch, make and fit a new bottom of plastic or resin paper, or even fibreglass filled epoxy circuit board material if you can get it (remove any copper conductors) have a bandsaw available to shape it, rebuild and and reinstall the switch.

Please keep us informed of progress.

Cheers from Connecticut!

[cynic-al]

Thanks Ron. Seems fine internally. That would be a nice fix, but I was thinking of washers to keep the contacts away from the footwell, given that the switch outer casing is earthed through the fixing screws in any event.

[JP 1800]

I replaced my foot switch last month and there was no backing insulation on mine also, those switches are of the Lucas type and are very poor quality. I got a replacement Bosch switch from Brookhouse which comes with an insulating rubber backing and are a direct replacement but of much higher quality. The switch only cost £19.50, the spade connectors will need to be cut as the Bosch has screw type contacts. I hope this helps.

[Ron Kwas]

JP;

Thanks for additional input...I would have though that the bottom cover was surely missing ( I presumed they had one...its been a long time since I closely inspected one), but if that switch didn't have an insulated bottom cover from the Lucas factory to begin with, the timebomb was courtesy of the poor Lucas design...curses on them (again)! This means that the terminal to which the Blue wire is attached is quite close to the (metal) mounting surface...all it would take for the electrical contact to occur is a little additional bending (from contact by shoe or carpet maybe). Perhaps that's what happened on Al's vehicle.

Al; I would still add a bottom cover, but perhaps an additional insulated separator to keep terminals definately separated from sheetmetal.

Cheers

[Derek UK]

I've never seen an insulator cover on these but it would be a good idea and easy to make from rubber sheet. Fixed properly/solidly and with good insulated connectors on the wires they should still be OK. I don't go along with the "poor quality" decription. There are plenty of cars out there still using the original one.
The one I have at the moment is the same as JP's and is either Bosch or Hella. Not round, has an alloy body and with screw terminals. It does work a bit smoother than the Lucas one but the difference isn't that noticeable when you're mashing it with your foot!

[Ron Kwas]

Derek;

This is the first time I've heard of this mode of failure of the switch also...but having not seen the exact cause of short (bent contact which allowed contact to chassis, loose terminal which contacted chassis, etc....maybe Al can provide some more specifics) I maybe shouldn't comment on the design...I probably can be accused of being predisposed to hating them, but this is not without (other) well known reasons...

Cheers

[cynic-al]

There is an explanation.

To stop the contacts shorting on the footwell & in place of the base, two screws went through the original mounting holes and screwed into thin metal tabs to hold it all together. The tabs extended outwards and further screws went through them into the footwell. However one had come off and the whole assembly was moving, this allowed the blue wire to short against the footwell. Hope this makes sense - someone basically made a stupid bodged repair that was doomed.