What gauge wire do I need to use?
I've gotta run a new wire from the first glow plug, through the firewall, to the indicator. It's a 73 220d, no relay, just a straight run from the "salt shaker" in the dash to the first GP. Thanks for your help!

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1973 220D

I'd use 6 or 4 AWG (American Wire Gauge).

I hope you are not going to bypass the fuse.

I haven't been able to find the fuse! I know it's on the firewall somewhere.
I thought the fuse was between the battery and the gorilla knob, am I wrong about this? Is it between the salt shaker and first gp? the diagrams I'm working from may be incorrect.

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1973 220D

I believe it's mounted to the firewall.

Here is a picture from DieselGiant

I believe your model still incorporates the ballast resistor...if you still use series glow plugs,you need it,if you`ve upgraded toparallel glow plugs,you do not-you put the 50A box in its place...The manuals recommend minimum 6sqare mm. thick wire between the plugs,however I `ve noticed the wire coming to the plug of cylinder n-r 4 is not that thick(in either case-parallel/series)...maybe 11awg. I think 10AWG wouldn`t hurt anything...
Some more info:
http://en.wikipedia.org/wiki/American_wire_gauge
http://www.dieselgiant.com/mercedesdieselloopglowplugrepair.htm