If the clutch engages when you apply 12 v directly to it,sounds like it is working ok. Maybe the resistance of the clutch is higher than the scale on your meter and you should try it on a higher scale. If the clutch engages,it has to have a resistance. May be one of the other interlocks. Am sure others on the board can help you a lot more.

What do you mean by "cannot get an ohm reading from the clutch"? I'm guessing the clutch should draw 2 or 3 amps which suggests the resistance reading should be somewhere around 5 ohms (Ohm's law). Are you saying there is no resistance?

With the tractor switch off I connect the ohm meter to the wires from the clutch and it reads 0.00 This is the same reading I get when the meter is turned on and the probes are touched together / no resistance.

Try reversing the leads of the meter to see if it shows "no resistance" no matter which way the leads are connected. Some of these PTO clutches feature a diode in the clutch wiring. The diode (if present) is to shunt high voltage "spikes" to ground. If a diode is part of the clutch, and the clutch is GOOD, you will read "no resistance" connecting the meter leads in one configuration, and when you switch the leads (polarity reversal), you will read the true Ohms value of the clutch coil windings. The Ohms value seen should be near the range of 2.4 Ohm and 2.9 Ohm. Anything much greater than 2.9 implies poor continuity through the windings. Anything much less than 2.4 implies "a short" to ground. If a diode is featured in the clutch, and the diode "shorts out", it will give the same Ohm reading (no resistance) as a shorted coil winding. Are you disconnecting the clutch wires from the chassis harness to access the terminals of the connector? Simply slipping the meter probes into the connector while it is still plugged to the chassis side harness will give a false reading.

When I engage the pto on my John Deere nothing happens. I can hook jumper cables off my jeep up to it and the pto will work but as soon as I take one of the cables off the pto quits working.