replaced the starter motor and cleaned all wiring to it batterys are all new and ful of power but still wont start, i wiggled the starter relay and starts first time, got new relay but still same problem, what else shall i try??
make sure its correct relay,[4or5terminals] if relay is plugged direct into relay/fuse board then it could be a faulty soldered joint inside fuse board assy.also have you ruled out cab tilt switch - this is the one that wont let you start engine with cab tilted. another check is alternator wiring,make sure none are broken or insecure [forms part of starter circuit]
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Try fixfault.com to fix lorries/trucks.