The control side of traction speed, 12v goes throught door switch, brake switch, sas or belly switch, fwd or rev switch,back down to terminal bd in the middle up to contractors, any resistance in that circuit , doesn't allow enough voltage to operate coils of contractors, low bat volts, bad switches, bottom of mast switch, or bad switch above b contactor, not supplying -ve to c. All have a bearing on 3rd speed.
All lift pump motors are serviceable, and should be checked every service.brushes are replaceable.
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