[Excaliber]

The solenoid and the regulator have little or nothing in common.

One "regulates" the rate at which the battery is charged, thats all it does. You either have a full charge or you don't. Charging the battery externally or jumping it will provide enough power to run\test the solenoid.

Assumming you have a fire wall mounted (typical) FORD solenoid:
The solenoid is an electromagnetic switch that allows the power from the battery to flow to the starter, which can draw around 90 amps of power. So you need a BIG switch to supply that power. Testing it is pretty straight forward. Use a jumper wire (or simply a screw driver) placed across the small terminal marked "S" and the main battery terminal (LARGE) of the solenoid. This makes the electromagnet engage and you should be able to feel\hear the magnet inside "closing" the circuit and letting power flow to the battery. Of course your key switch IS the usual "jumper wire". The key switch simply puts 12 volts power to the "S" terminal and thus engages the solenoid magnet. If you have around 10 volts only, the magnet will "chatter" and not engage fully and the starter won't spin. The solenoid must be grounded to the car frame in some way for it to complete the circuit and "turn on".

The regualtor test is NOT easy. With the engine off take a volt meter reading at the battery. Say you get 11 to 12 or even 13 volts. Start the car (if you can). The voltage should increase to 14, perhaps a high 13 volts if the battery was pretty low all ready. If the battery volts DO NOT increase it could be the alternator is not supply power and the regulator is fine. If no voltage increase I would take the alternator to your local "Parts Store" and have it tested. If it checks out OK, then I'd likely buy a regulator. Of course check carefully to make sure the regulator and the solenoid have a good engine\frame ground first!

Testing a GM style solenoid which is mounted (typically) ON the starter is the same procedure as a Ford. But of course is MUCH more difficult to access!