Thread: Can the fire wall be used as an earth???

There are a number of earth points on the D2. From memory there is one on the firewall. If its not the battery earth it shouldn't pose an issue, but I wouldn't earth the battery back to there.

Your best bet is to PM or phone drivesafe (Traxide) and ask him directly.

hi Matt

I would take the earth from the aux battery to a bolt on the engine (i really need to work out how to post photos!)

as a sparky, i would earth the body (the firewall or anywhere else) and the chassis.
no point earthing the engine, unless it is going to run off the aux battery.
the engine, chassis and body are all earthed from the main battery, so althourh you may not need it, the engine will be earthed to the aux battery anyway.
bear in mind that the "earth" as is colloquially known is actually the negative path for the battery circuit, which uses the metal in the car's body as a conductor.
keeping this in mind and the fact that the positive will be of no use at all without the negative, might help you in understanding the function and reasoning behind the connections of the earth and their importance.

a poor termination of the cable, whether it be a bad crimp or bad contact into the metal of the body (use a star washer for better effect), will create heat, whih will slowly get worse until either the wire burns off or your car bursts into flames.
have a nice day

Hi, I ran a decent size cable - 35 sq mm along the firewall across the top of the engine (cable tied onto the brake lines) and down the right side to the main earth point adjacent to the TD5 ECU. This then ties all earths together to one common point.

Connecting the 2nd battery to a riv nut or self tapper on the fire wall may be OK for a while but if you get any corrosion you can get unstuck.

Erich

barney,

why would you earth the body (the firewall and anywhere else) and the chassis when you say they are all earthed together anyway?

beacause copper cables provide a much better path to all those little electrons than the various bad joints ( in electrical terms ) between panels and between panels and chassis.

As said before, the term "earth" is bit of a misnomer when applied to DC currents in motor vehicles, considering they are well insulated from the "earth" by big rubber tyres. It is the negative side of your circuit, and just as important as the positive side running via the wires. Using the car body to complete one side of the circuit ( either positive or negative ) really was a cheap way of getting out of having to run two wires to every device from the battery. The practice has kept the auto electricians in a job for decades tho , finding "earth" problems.

The idea of a common "earth" point where all your negative cables come together, is that the circuit is completed via cables, not the car body.

And especially important when you realise that power actually flows from Negative to Positive

Originally Posted by Tombie2

And especially important when you realise that power actually flows from Negative to Positive

electrons run from negative to positive