I have a 50hp thunderbolt 1982. I get over 12 volts to the large solenoid terminal. theres like 3 volts to both the small terminals key on but not cranking. is this the norm?
No. There should be 12 volts to the small terminal at cranking too. Zero volts with the key in the run position. Go over to the Merc forum and ask about correct wiring, interlock switch, ignition switch, etc.