Hello everyone i was wondering if someone could help me figure this out. I have a massey 6180 1997 8000hrs but in great condition. the 4wd will not engage but lights and everything seems normal. I checked the shaft and couplers, I jacked up 1 wheel at the front when tractor not running and the wheel wont turn, then I start the tractor and the wheel will turn which tells me the 4wd pack is good and the solenoid is working, however when the the tractor is running there is 12v permanently at the solenoid plug, i also swapped the 4wd switch with the Difflock switch and swapped solenoids etc but still the same. Is there a relay or sensor somewhere that sends the signal? any photos or help would be great thanks.