The quick test for starter/solinoid is to bring battery power to the center terminal of the 3 prong plug at the firewal next to the booster [ left of the booster, the wall between the engine and booster]
This is starter feed after NSS and ATA.
If that works, work back from there .
My first try would be N instead of P .. suspect is NSS ...very common on 124 shassis of age/miles..