Kwangtzu,
I haven't been following this thread closely. I'm going to make some assumptions which might be wrong. Your truck is a 12 volt system with a stomp starter. If you don't have a internally resisted coil then there should be a ballast resistor on the firewall and a terminal on the starter switch which acts as a bypass terminal.
If you turn the key ON, the coil should be powered. If you turn the key OFF, there should be no power at the coil. The presence of voltage would be measured with a voltmeter from the key side (+) of the coil to a good ground.
If there is a ballast resistor in the primary circuit to the coil it will be bypassed when you push the stomp starter down. This powers the coil directly from the small terminal on the starter switch. There should be only one small terminal and only one wire on it. This wire would go to the coil OR the coil side of the ballast resistor.
I believe trucks of this year equipped with solenoid starters had a rather involved key switch that feed full voltage through to the coil on START. Your truck evidently has a stomp starter which would involve a ON-OFF-ACC key switch. The coil should not be powered in ACC either...only in ON.
I usually ground one probe of the voltmeter or ground the alligator clip of the tester and search for powered wires or connections with the other probe.
Stuart
