Power Wagon [886] Ambulance wiring question !!

IGNITION SWITCH. I would cut the "run" line coming into the engine bay and add a bosh relay. Wire the relay coil to the "run" wire on the firewall side of the wire. Hook the engine bay end of the cut wire to the switched contacts. Feed the relay power from the starter relay "big stud" through a fuse or breaker, about 20A

This will relieve load off the key switch.

Also investigate---since this is an ambulance--other added loads on the ignition switch that you maybe ought to add relays to drop those loads off the key.

It is rare but even that welded splice--under the dash--in the black ammeter wire....can and has failed