Leave the connector connected, prick the Blue wire with the positive lead and the Grey wire with the negeitive lead, should read close to 5 volts. Often lower voltage, XJ´s are old.
Disconnect the coil and have osmebody turn the notor over a few times the volt meter should pulse.
I´ve never done this test mayself, just repeating the test procedure.
I´ve foregotten and ran my XJ for days without the Cam position sensor connected? I don´t really know hoe critical it is or if it actually does anything.