TE20 earth / coil questions

Sounds like a negative earth system... but I'm confused by a couple of things. First, I think the tractor still has the original 6V coil (it gets *really* hot, sparks at the plugs are feeble and it won't spark for hours when it's been running a while); one side is connected to the points (as you'd expect), but the other is marked (-) - that's where I connect the positive terminal of the battery.

How likely is it that this is the old coil, and the tractor switched from positive to negative earth when it was converted to 12V? I assume this must be the case, as the starter wouldn't crank properly if it was connected with the wrong polarity (would it?) Saying that, it's always been difficult to start, though I've always put that down to a poorly coil and a badly tuned carburettor. I'd feel pretty stupid if I'd been starting the damn thing by cranking it the wrong way all this time...

If I'm right, and it is negative earth, would a new (12V) coil give me stronger sparks and greater reliability? I've given the distributor and the plugs a lot of attention, so I imagine it's the most likely weak point.

I'd be very grateful for any information and ideas (not to mention a good 12V TE20 wiring diagram) -- thanks to all who have posted in this forum for a lot of really useful information.

• TO-30 12v wiring diagram (- ground)

teadave

If I was wrong about the conversion, and the tractor was 12V from the start, would I still need this?

Many thanks for your helpful reply - I won't chuck the coil out just yet!

Christian

• Link

Serial number is TED268089, and I have a scrap of paper documenting the first sale of a '1952 Ferguson tractor', so I assume so. I'm guessing on the conversion - it may always have been 12V - but if so, I can't explain the (-) marking to which I connect the battery. The regulator looks newer than most of the tractor, too - although that's far from conclusive.

> Regarding the weak spark and poor starting check coil/condenser/points/distributor cap/HT
> lead.

I don't really know how to check the coil, but I've pushed it so much (and without the 'ballast resistor' mentioned in teadave's reply) that I think it may need replacing anyway. The condenser is the little capacitor thing by the points, right? I could test its capacitance - does anyone know what this should be, or is it just a case of buying a new condenser? Points / distributor cap / HT lead should all be good - I put a lot of work into cleaning them up, and there's a good spark at the points.

> I thought that with a positive earth system the lead from the positive on the coil should go to > the distributor. If negative earth system, the coil negative lead would go to the distributor.
> Again perhaps others can provide their thoughts.

I'm relying on a legacy here - the tractor was in a bad state when I was given it (although I'm assured it did run well, and the cabling has done nothing but corrode since then). The only intact lead on the whole damn machine goes from the points to an unmarked terminal on the coil. The other coil terminal (to which I connect battery +ve) is marked (-).

If the starter motor is rectified, what would be the problem with connecting the battery the wrong way round (provided the connections to the rectifier were switched accordingly)?

Many thanks

Christian

Somebody had pinched the battery when before the tracrot was given to me, but it has a 12V regulator so I'm fairly sure that at least the battery should be 12V...

> If you have a generator it would be a positive graound. If you use a negative ground for your
> battery connect the wire from the distributer to the negative terminal on the coil.

It has a generator, not an alternator, but some other posts on the site suggest that this arrangement is possible with a negative ground system. I'm loathe to move the points cable to the negative terminal on the coil without full details of the correct wiring system, as I'm told it always worked fine when connected to the other terminal. It certainly starts and runs if I connect it negative ground with the points cable leading from the distributor to the (+) terminal of the coil, but of course I haven't tried hooking up the generator and the regulator yet...

This is all a bit of a mystery!