Need 12v switched power in engine compartment 85 300TD
 

Can any one tell me where I could find a good circuit to tap into? The fuse box is close but wires are pretty inaccessable on the other side of the firewall and buried behind the steering column. I need about 17 amps as its running a heating element on a Veggie fuel filter.

TIA John

It's easy
 

Try dropping your light switch and finding a terminal that is hot in "on mode" only. Then snake that single wire through the firewall rubber plug to a standard Bosch relay like the ones sold for fog lights etc. Use an inline fuse from the battery to the relay.

I guess you could tap into the supply terminal in the glow plug relay? Its before the 80 amp fuse and has a heavy duty wire running into it.

Where exactly would that terminal be? The other option I just noticed is on the left side of the fuse panel between the window motor fuses is a screw hole that is switched. I assume the glow plug circuit would be better; the terminal is in front of the relay, correct?