Your rig being a 78 , it "should" have the ballast wire. The ? is . Is the wire to your resistor connected to the ballast wire, or some other direct 12v wire.
I had a 60 that used to run like a dog when hot. After some digging , the PO had wired the ignition module from the coil+, witch was only 10v.
Full 12v fixed it. This must happen a lot IMO.
Only the coil + should be connected to the ballast wire. Any other electrics need 12v. Relays might be ok. They seem to activate as low as 5v sometimes.
I had a 60 that used to run like a dog when hot. After some digging , the PO had wired the ignition module from the coil+, witch was only 10v.
Full 12v fixed it. This must happen a lot IMO.
Only the coil + should be connected to the ballast wire. Any other electrics need 12v. Relays might be ok. They seem to activate as low as 5v sometimes.