The Fordson Tractor Pages Forum

The 'Chief Banker" of the family told me she wanted to use the Dexta to do a small job, being a cold morning I started it and warmed up the engine to make it easy for her. Unfamiliar with our blue darlings she then closed the fuel tap I had left on, drove off and ran out of fuel on the roadside. Trying to restart she ran the battery flat, removed it and replaced it with a new one, wiring it negative earth as she went, not realising it had been positive earth.
The question now being, would this have done any damage? I did restart the engine today but the green light does not go out.
Am I best to return the system to pos-earth?
Many thanks.

By reversing the polarity of the system, positive to negative earth, without polarising the dynamo, it is possible you have fried both regulator and dynamo. Put it back to positive earth, polarise the dynamo by flashing a wire from the output (live) side of the battery to the field terminal (small) on the dynamo and see what happens, you have nothing to loose.

You could also leave it as it is and flash the field terminal, that will change the polarity of the dynamo to negative earth. When doing the flashing the dynamo should have no wires on either terminal, just bolted to the tractor.

You may find everything is OK but be aware that you could have welded the points together in the regulater. If so, the back feed when the engine is stopped will try and make the dynamo run like an electric motor. If the fan belt is loose it will just turn and run the battery down, if the fan belt is tight, the dynamo will not turn and the wiring may heat up and catch fire. Seen that happen too many times. It may be best to slacken off the fan belt and see if turns like an electric motor, if it does, the regulater needs replacement.

On a Dexta, the red lamp should be the charge light and the green the oil pressure, that is how they left the factory, hope yours has been reversed.