Re: ignition coil
It is probably time for an electrical tuneup involving replacing the contact points and condensor and setting the dwell and timing.
A coil will have voltage showing at both positive and negative terminals, they are the ends of the primary coil of wire inside the coil and as such are directly connected. The coil is really a step-up transformer that ended up being called just "the coil". There are two coils of wire inside the coil housing, they are called the primary and secondary circuits. The primary coil is connected to the positive and negative terminals. The way spark is generated is the positive terminal gets 12 volts all the time (really more like 9 or 10 after the ballast resistance is considered) and the negative terminal gets grounded and ungrounded thru the contact points inside the distributor. This causes a magnetic fiield to be generated from the primary coil and then collapse when current is interrupted. The secondary coil has way more windings than the primary coil. When the voltage thru the primary is interrupted the magnetic field lines from the primary collapse and induce a voltage in the secondary. Since there are more windings in the secondary the voltage is stepped up. The spark plug and coil "high tension" wires make up the rest of the secondary circuit. One end of the secondary coil is connected to the coil tower and the other grounds thru the same negative terminal as the primary coil. The coil high tension wire goes from the coil tower to the center of the distributor and gets sent to the proper cylinder's spark plug high tension wire thru the rotor.
A standard coil can be checked easily while on the engine. Remove the negative connections. Connect a longer wire there, one that you can touch to a suitable ground. Disconnect the "big" coil wire at the distributor and place the metal connector inside the boot near a suitable ground but not touching it. Make sure is it not near a source of fuel like the carb or fuel pump or lines. Turn the key on then touch the wire from the negative coil terminal to to gound. When you remove the wire from ground after it has been grounded for a second or so there should be a spark generated at the end of the coil wire. It should work like a telegraph key, touch to gound and remove in rapid succession and the sparks should literally fly.
The spark should be blue and be able to jump 1/4 inch or so. It is best observed in the shade or in twilight or nite time conditions.
