The Fordson Tractor Pages Forum

Hi All I'm hoping somebody can help me with bit of basic advice

On my Super Major the dynamo has been swapped for an Alternator and my battery is not charging
I have 2 wires coming off the Alt
1 seems to go to the solenoid but can't find the other wire
I have no light on my dash lite up
When I put a multi meter across the battery with the engine running it is only showing 12.5 volts I would have thought it should show around 14v if it's charging

Many thanks
Jim

I think... power should come from your ignition switch, through the ignition light, and then to the small terminal on the alternator?

And I think, that this should be similar to the dynamo, so the existing wiring shouldn't have been altered too much. The output from the dynamo would have went to the control box/regulator and then to the solenoid; whereas the alternator has its regulator built-in, so the output can go straight to the solenoid.

I have been led to believe that alternators don't like being run not connected, so yours may well not be working anyway.
As a first step - if you earth the small wire at the alternator with the ignition switched on, the red light should come on. If it doesn't, then check the bulb and wiring. (a 12-volt sidelight bulb will do if you can't find a correct replacement right away).

As an aside.. my Major also came with an alternator fitted, but with the tractor's original (dynamo) pulley fitted to it. It did charge (the red light and ammeter are both working), but only when revved-up. Alternators seem to need more rpm's than dynamos, so I found a smaller pulley (and shorter belt) and everything now works much better, the red light now goes out straight away.

I can have a look to see what has been changed on my wiring if it helps, this is not a Power or Super Major so the instruments are different, although the wiring should be similar to yours. It is easy to find a wiring diagram, just Google it if you don't have a manual.

on a dynamo the earth is +, on the alternator it should normally be negative. Did you check this?

The fat wire (+ve) from the Alternator should go directly to the battery side of the solenoid.

The thin wire from the Alternator should go to the Alt warning light and thence to the ignition switch.

The alternator body should be earthed to the tractor chassis (-ve).

Thanks for the advice,
My wiring loom looks like normal household cables nothing is wired to the ignition switch,
To start the tractor I just push down on the lever
Think I might have to buy a new loom and do a total rewire

Jim

Ahh... yes I think you need a whole new loom, then work from there. You 'should' have to switch on the key before you even get the tractor to start.

Jimbratt wrote:Thanks for the advice,
My wiring loom looks like normal household cables nothing is wired to the ignition switch,
To start the tractor I just push down on the lever
Think I might have to buy a new loom and do a total rewire

Jim

Jim,

Or you can make you're own.
This is for the normal setup: (for the alternator you have to switch the poles and forget about the regulator)

If you want a new harness, I got mine (Dexta) from Autosparks. I can recommend them. All colours as per original. Got mine made without end terminals, so I could solder on my own. Got all my terminals from them too.

An alternator needs to have a voltage applied across it before it will start producing power - if you read battery voltage between the thick lead AT THE ALTERNATOR and the body then it ought to charge when spun up - I have one coupled to a Suffolk Punch lawnmower engine for battery charging or supplying 12v for lighting or amateur radio and if I haven't taken a 12v battery with me, I have got it to kick up with a not very new AAA cell across it, mine is a Lucas and voltage to either the thick or the thin lead will energise it but not all alternators operate the same.

Its also worth checking the slip rings and brushes are intact as they take a caning on a tractor

So if I go for a new harness,what do I do with the 4 wires that would go to the regulator
And would I use all 3 connections on The Alternator or just 2 of them
Would like to know before I go and buy a new harness as will also have to buy an ignition switch and horn button and horn
Starts o get expensive

Thanks Jim

See the wiring diag for my Dexta with alternator, described in this thread. Your Major should be pretty much the same.

http://www.fordsontractorpages.nl/phpbb ... php?p=8390

I left the four unused wires (DEAF) in the new harness, but just taped up the ends to keep them out of the way. I also included an auto resetting circuit breaker, similar to used on a Harley Davidson bike.

Thank you so. Uch for the advice
I will order a new wiring harness now I know what to do with the wires

Cheers
Jim

Do make sure you get a decent harness, no scotch locks or similar. Soldered terminals are best and will last for years - nothing worse than dodgy electrics!

I actually fitted a non-standard 'ignition' switch, a Hobbs Honeywell 848289 3-position key switch:

https://uk.rs-online.com/web/p/products ... lsrc=aw.ds

Lights are on a separate lights-only switch (as for a Super Dexta). This is a much more weather proof set up.

I like your switch Ben, I may have to do the same in time.

Mervyn Spencer wrote:I like your switch Ben, I may have to do the same in time.

I installed the switch in the usual Super D position, on the RH side of the lower inst panel. Fits neat and tidy.