# Fordson Dexta 1956 electrical help



## Martin Weston (Mar 8, 2020)

Hi,

I'm having some trouble with the key switch.

The first symptoms were having to wobble the key to find a place that would allow it to start but now it is broken and wont allow it to turn over at all.

I have taken the cover off, there are some disconnected wires but I think they are just un-used ones but the red wire looks to have melt damage!

Pics below:
https://imgur.com/a/aOT3zIJ

https://imgur.com/a/ZqyNO7H

Can you offer any advice please?

Best,
Martin


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## pogobill (Jan 31, 2012)

Welcome to the forum Martin. You may have to replace the ignition / lightswitch then you may need to open up the wiring section that is taped up with blue tape to trace the red wire or any others that may be damaged. Something is causing the wire to overheat.


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## Martin Weston (Mar 8, 2020)

Hi,

Thanks for the reply.
I have ordered a replacement switch and will investigate.

Perhaps it is the heating button used to aid starting? Can you hold it down "too long"?


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## Fedup (Feb 25, 2014)

I can't believe a properly functioning manifold heater would draw enough current to damage a wire that much. The wire in the photo you posted appeared to have been the victim of pretty much a dead short to ground. Is the melted wire connected to the same post/terminal as the large brown wire next to it? Is the brown wire by chance a battery wire?


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## Hacke (Feb 22, 2011)

You call the switch "starter switch". How do you start the tractor, only by that switch or do you use a lever on the side of the dash to engage the starter after you have switched on this switch?

Normally this switch is a combined "ignition" switch and light switch. You turn on/off the power with the key and control the lights with the lever on the switch. It looks like this:
https://www.agrilineproducts.com/ford-fordson-ignition-light-switch-5071a
Then you engage the starter mechanically with a lever on the side of the dash.

The only wiring diagrams I have found is on this German site:
https://lumpf.jimdo.com/traktoren/schaltpläne/

There were different wiring for the Dextas during it's time, but I guess this one will be OK:
https://image.jimcdn.com/app/cms/im...1dc28877a55b3d60/version/1485424851/image.jpg
It is the diagram for Dexta without indicators, 1958 to 1960
("elektrischer Schaltplan Fordson Dexta ohne Blinkanlage 1958 bis 1960")

The wiring that is disconnected from your switch has to do with lights.
*** Edit
Only lights.
***

Your yellow cable seems to be the yellow with red tracer (Y/R) that feeds the switch from A1 at the voltage regulator.
The brown cable and the fried red cable that goes together at the switch seem to match the diagram.
The brown (BN) goes to the push button for the intake heater.
The fried red (3R) goes to the starter contact.

When you pull (or push?) the starter lever, the starter drive gear engages and the starter contact closes (3R) to (2R). (2R) is connected to the starter solenoid (Magnetschalter) that pulls the contact that gives power from battery to the starter, and the engine cranks.

If all this is true, the problem with the fried wire is either a short to ground along the way to the starter, a faulty starter contact or a faulty starter solenoid. It could, perhaps, be the faulty key switch that has not been cutting off the red cable properly, and the starter contact is leaking to ground.

Anyhow, check/fix the wiring and try the new switch.


This is a good source for information regarding the Dexta in general:
https://tractorspares.ie/tractor-manuals/


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## Martin Weston (Mar 8, 2020)

Hi,

Many thanks for the post.
It makes sense cheers.

It's ignition switch.
I use a starter on the side. When the switch is turned off (or not successfully wobbled into a working position) the side starter doesn't do anything. It now wont wobble to a working position.
I have no lights so only used as ignition (you noted this in your post).


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## Hacke (Feb 22, 2011)

By the way, if the cable (2R) from the starter contact to the starter solenoid is OK, the solenoid is probably OK.


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## Martin Weston (Mar 8, 2020)

Hi,

Your interpretation of the diagram was correct.
The red wire ended up being damaged right down to the starter contact.
I replaced the switch and the red wire (using a slightly heavier wire in the replacement) and it all seems ok now. I have not taped the red wire back in with the others so will monitor its condition.

Thanks for the help.


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## dexy (Aug 28, 2020)

It would be helpful if the designations would be used as reference. I'm also having trouble connecting wires. It seems like new wiring looms are for Dexta's with light-switch and key-switch separated.

Anyway, the connector in the middle is called COIL (red wire?) whereas the wire from AL is supposed to be connected to BAT. But new wire trees are pre-connected e.g. blue/black wire combined with the red wire.


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## Martin Weston (Mar 8, 2020)

Hi,

I can confirm the starter is still working for me, with no sign of the wire cooking again.


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## dexy (Aug 28, 2020)

Have you already tried the lights? My green-black wire and also the AL-BAT wire melted when switching the lights on. Here is the schematic that came with my wiring loom.


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## Hacke (Feb 22, 2011)

Judging from your avatar, your Dexta is pre 1962?

That diagram is a bit strange, I enclose a pdf with some comments. Not that it explains why your wires melted. That problem is more likely a short to ground at the headlights, or in the harness.

To be certain of the splices in the harness, I would test connections for continuity to be sure it is alright.


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## dexy (Aug 28, 2020)

Hacke, thank you for your confirmation. I came to the same conclusions as what you marked on the diagram. One additional note: the connectors to the control lights and rear lights in the diagram are swapped. The black/blue wire should feed the control lights whereas the black wire should feed the rear lights.

Thanks again.


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## rob77 (12 mo ago)

Hacke said:


> Judging from your avatar, your Dexta is pre 1962?
> 
> That diagram is a bit strange, I enclose a pdf with some comments. Not that it explains why your wires melted. That problem is more likely a short to ground at the headlights, or in the harness.
> 
> To be certain of the splices in the harness, I would test connections for continuity to be sure it is alright.


Hi, thanks for posting the correct wiring diagram, I was struggling with the “official” version! Yours is almost right… the only problem I found was the dash lights were on permanently, even with the key in the off position. The labels on the part of the loom that feeds the horn and dash lights are the wrong way round for oil light (should be blue/black) and rear side lights (should be black). Once they were swapped we were back in business, thanks for helping a mechanical idiot to rewire a tractor!


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## rob77 (12 mo ago)

dexy said:


> Hacke, thank you for your confirmation. I came to the same conclusions as what you marked on the diagram. One additional note: the connectors to the control lights and rear lights in the diagram are swapped. The black/blue wire should feed the control lights whereas the black wire should feed the rear lights.
> 
> Thanks again.


Yup, what he said!


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## Hacke (Feb 22, 2011)

rob77 said:


> Hi, thanks for posting the correct wiring diagram, I was struggling with the “official” version! Yours is almost right… the only problem I found was the dash lights were on permanently, even with the key in the off position. The labels on the part of the loom that feeds the horn and dash lights are the wrong way round for oil light (should be blue/black) and rear side lights (should be black). Once they were swapped we were back in business, thanks for helping a mechanical idiot to rewire a tractor!


Sorry, I never updated the diagram. I will do that now, but first a question about the feed from Control Box (Voltage Regulator) to key switch. I attach a picture showing the smaller harness. There is some wires taped onto the outside of the harness. One of them has to be the yellow/white (or is it yellow?) wire for the charging warning light, that is supposed to connect to Control Box (D).

What else is there? It looks like it is a short loose wire, is that the yellow/green that is supposed to be connected between the regulator (A1) and key switch (BAT)?

After my latest post, I found a wiring diagram that I think is the correct one for the Dexta variant that the aftermarket harness is for. Attached as a PDF.


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## tomgill84 (10 mo ago)

Hello,
I'm so pleased to have found this forum! I am rewiring my 61 Dexta with the agriline wiring harness and have got stuck when wiring the key/light switch! Could someone confirm what wire goes from the Bat terminal?
The above improved wiring diagram is a huge help!! Thank you


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## Hacke (Feb 22, 2011)

tomgill84 said:


> Hello,
> I'm so pleased to have found this forum! I am rewiring my 61 Dexta with the agriline wiring harness and have got stuck when wiring the key/light switch! Could someone confirm what wire goes from the Bat terminal?
> The above improved wiring diagram is a huge help!! Thank you


It is a mess altogether. This is what I have found out so far:

There were two different voltage regulators used on the Dextas. RB 106 and RB 108:





Lucas Regulators


Electrical wiring products, parts and accessories for vintage and classic cars




www.autoelectricsupplies.co.uk





Some tractors had "ignition" key switch and light switch combined.
Some tractors had "ignition" key switch and light switch separated.

In the diagram that follows the harness, instructions and colours for the different systems have been mixed up. Look at the original diagrams I have found so far, in the attached PDF.


As far as I know:

If you have an RB 106 regulator (E D F A A1) and a combined key/light switch, BAT is fed from A1.

If you have an RB 108 regulator (E D F A) and a combined key/light switch, BAT is fed from A. With this harness, A also holds the yellow wire from the "main harness".

If you have an RB 108 regulator (E D F A) and key switch and light switch separated, BAT is fed from A. With this harness, A also holds the yellow wire from the "main harness".


For the BAT connection, I would make my own wire. I suppose one of the taped pieces is meant to go there, but make sure you use at least a 6 mm² wire.

I would also put a fuse box in the system, to protect and separate the wiring. Do as you like, but it is easy to use an inline fuse on the BAT connection to give some protection:








Durite Splashproof Maxi Blade Fuse Holder With Cover - 50A Max.


Inline fuseholder for use with higher current Maxi fuses. Comes with rubber splashproof cover and 6mm2 tails for connection. 50A continuous & 100A intermittent.



www.12voltplanet.co.uk









MAXI blade fuse holder


Electrical wiring products, parts and accessories for vintage and classic cars




www.autoelectricsupplies.co.uk


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