The Fordson Tractor Pages Forum

Although my Dexta works fine in the electrical department (except for the lights and horn) there are lot of wires that look like they are about to come apart at any minute and so I am going to rewire the whole thing.
Before I start taking wires off the tractor I would like to understand what they are all for (i would hate to have a working tractor that stopped working due to my attempts at fixing it).

The generator has no markings on it at all just 2 terminals, a larger one and a smaller one, which have a wire each which disappear into the wiring loom and seem to come out where they are supposed to (although it is hard to be certain as it seems that some wires have been repaired with different colours and then all painted over). There is an extra wire which connects the 2 terminals on the generator to each other. This seems wrong to me but the tractor is running and charging fine.
Why is this wire connecting the terminals on the generator?

I don't think it should make any difference but the tractor is negative earthed.

Thanks

I suspect that your regulator is not working and by connecting the Field (small connector) to the Dynamo output (Large connector) the field winding is always energised and making the generator produce an output. If you disconnect the shorting wire and monitor the Dynamo voltage it may well not be giving sufficient output to charge the battery. Remove the regulator (disconnect your battery first!) and remove the cover and without mechanically moving (bending/adjusting/altering) any part use a piece of 1000 grit wet and dry paper, polish the contacts. They may have corroded over time. Also the screw connectors into the dynamo may be loose/poor connection. Check these.
There is a wiring diagram for the original Dynamo setup in the downloads section and there is my wiring diagram available for a more modern wiring with an Alternator, brake and indicators.
Jerry

As for a re-wire, a complete new loom is not excessively expensive and easily available

Thanks for the reply. I will have a go tomorrow at checking the regulator voltage and all the contacts.

I have a new loom and have been trying to match it up with the wiring diagram and then comparing it with the existing wiring before removing the old wiring.

If the colours of the wires in your new loom match the originals, then matching it to the wiring diag is easy!

I have finally gotten a rainy day to spend in the shed on the tractor and have fitted a new wiring loom.

I checked the voltage output on the dynamo and, wired properly, it is 3v at idle and 5.5v at speed which seems too low.
With the dynamo shorted between the 2 terminals the voltage (between the dynamo and earth) is 20v at idle and 40v at speed. Is this right? It seems quite high. Is there any down side to running it like this (will it cause any damage to anything?)

The dynamo has spade connectors not screw ones however I couldn't find any looseness.

I forgot to clean the inside of the regulator - perhaps that is a job for the next rainy day!

Thanks again

That would be correct! The Regulator is there to control the output of the generator to charge the battery but not overcharge it (this will damage the battery and cause the battery to give out gas which is explosive). Once the engine turns the generator above tickover then the regulator connects the generator to the battery and adjusts the voltage applied to the field windings. This controls the output of the generator (big terminal) to make the voltage slightly more than the battery voltage therefore forcing current (amps) into the battery to charge it. As the engine revs increase then the field voltage is reduced to adjust the generator output accordingly. I think your problem is in the regulator or the wiring. I suggest you borrow another regulator and try that.
The alternative is to fit an Alternator but that would require some extra work and rewiring!
Cheers
Jerry

You might end up having to get the regulator repaired or buy a new one, if youbuy new, don't throw throw the old one away, there are people (me included) who consider a repaired original much more reliable than a patern new one.

http://www.worldphaco.net/uploads/REPAI ... _RB106.pdf

Good luck with it.

Regards

Ian