What gauge of wire to use to safely manually trigger the starter or glow plugs?
 

This is for my 1985 300D.

I would like to keep a jumper wire in my car for use in the case that I might sometime get stranded with a failed ignition switch and/or neutral safety switch and hence, the starter not cranking or the glow plugs not glowing.

I would be using the jumper wire between the battery + terminal and the screw connections in the terminal block on the right front fender.

This might seem like a silly question but I'd rather ask and avoid getting burned or starting a fire:
What gauge of wire is adequate to carry the load when using such a jumper wire?

I'd appreciate any clarifications on this. Thanks-

Only the tubo models W123s have this terminal block in the attached picture in front of the battery.

See Attached picture. The 2 screws to the left are both eventually connected to the Positive Battery Terminal.

The forward to the right screw has a White Wire which goes down to the Starter Solenoid and a Purple (Lavender?) wire that goes to the Glow Plug Relay. If you jump from right to left the Starter starts cranking and the Glow Plug relay activates but will shut off as soon as you stop cranking.

A 14 gage wire ought to be sufficient. However, you will know by it getting hot if it is too thin of a wire or not.

If you want to apply the Glow Plugs before cranking that is more complicated.

I clip a remote starter switch similar to the one in the last picture to the terminal block and us it to crank the Engine during valve adjustments or for other issues. The wires on it are not thick. It seldom gets into the low 40s F where I live.

Great. Thanks-