I assume my 1975 300D is one of those odd "in between" years for glow systems. I have the old series type plugs with a key start system (i.e. not the pull knob glow/start system), but I do not have the 80 amp fuse in the engine compartment. With a little help from some forum members, I traced the glow plug power source back through the firewall to a caged relay (a little square box with a couple of springs in it, each with what looks like a thermal switch piece of metal under it). This device does not have any obvious faults, but I am not getting power to the glow plugs when I switch the key to the glow position.

The caged relay has four wires exiting to the engine bay, and two coming in from the dash area. Can I assume that the two coming in should carry 12 volts across them when the key is in the glow position? If so, I think I may have a faulty igition switch, as I cannot get voltage to measure at the relay at all.

Any advice would be much appreciated; as it stands, I have to jump the battery to the plugs to start the car (which works fine every time).

Thanks!

Chris
cscmc1@eiu.edu