Machine is around a 2007 and will not unlock posi drive or boom hydraulics. Had trouble finding a schematic of the electrical systems in these machines, but found a pdf here: http://www.tractorbynet.com/forums/parts-repairs/338666-asv-sr80-sr70-pt80-terex.html My wife took the file on a card to UPS and they blew it up to 2'x3' for easy reading. According to it all 12v coils on the stems in the pilot valve block should be grounded to the frame behind the seat. Machine is getting 12volts to both safety coils/stems (these coils unlock drive and boom hydraulics), but is lacking a ground in both. Traced grounds back to a plug in the wiring harness that continues to cab behind the seat so it has a variation in the electrical system. All other coil grounds go behind the seat to the frame. I am assuming the safety grounds are switched somewhere. Don't know why they would design them like this. Which leads to another variation...my seat switch and seat belt switch according the the schematic ought to be a switched negative circuit (grounded to the frame close by), but these have 12volts in them. Both switches when engaged separately trip their subsequent relays in the fuse panel, but when the belt is engaged it does not allow the seat switch to trip it's relay. Something weird is going on and it's been driving me nuts! Any help would be appreciated. I know I need to get a hold of the correct schematic somehow. Machine does not have the lap bar on either side.
Called Terex Service Department (218-999-4266) and they were very helpful. Machine took some of the SR80 and some of the PT80 electrical schematics to get the problem solved. They will email whatever you need, ASAP. Saftey switches in this machine are wired in sequence with seat switch having to be closed first, then seat belt, then both safety coils will have completed ground. Machine had one bad ground, terminals in fuse box cleaned and blown out, replaced two bad relays. All is well (for now). Now on to the dreaded lag in the drive joystick...Terex does not make a resolver block for this machine...says the only option is to replace entire joystick (850 to $900).