After a week of testing out the battery and starter, I am still struggling to get my 1979 240D to start. The starter is rebuilt (by a reputable local shop) and the battery is new.
Still no start.
After this whole ordeal, as well as testing and rewiring the GPs, a proper 50-amp fuse installed (the PO had pencil style GPs, old wiring, and no fuse), and cleaning ground wires, no start!
After attempting to start I go under the hood and notice there is absolutely nothing happening with the GPs. I can touch them; they are not even warm. I've tested for continuity, but when the key is in the ignition to glow the plugs, there is a most 1-2 volt current in those plugs.
What else can I troubleshoot? I'm starting to pull my hair out, especially considering it had no problems before I changed GP wires, added a fuse, and put in new return lines.