I have the original shop manual for the Dodge M350 and M375 Chassis with the electrical schematics. I have a 1974 Commander built on the M375 and had to replace the entire electrical system so I know your pain! If you give me an e-mail address I can scan the schematics and send them to you. On another note there are 4 or 5 wires that are located on the back of the ignition switch that come lose. Look under the dash at the back of the switch and push those back on, the are marked “B’ for battery, “I” for ignition, “S” for starter and so on. There is also a fuse block under there to your left. You can use a voltmeter to check the various positions of the ignitions switch and see if it is supplying power. If it’s the ignition switch e-bay has one for about $30.00.
Cole
