Tractor Split = electrical problems??

My TEA20 is negative earth, the battery earth lead is connected direct to the top starter bolt and the lead terminals are clean and bright.

Years ago, when both my tractor and I were kids, battery leads were heavy guage wire and had soldered and crimped terminals. The terminals were tinned brass, less susceptible to corrosion. These days battery leads are small guage wire with crimped steel connectors which are very susceptible to surface corrosion.

Also often overlooked is corrosion at the leads and connectors on the gear lever activated starter switch in the bell housing.

My guess a starter motor must be around 2 or 3 horse power. At 12 volts, 2.5 horse power (1,875 watts) the current draw is 155 amps. (Halve the voltage to 6 volts on early tractors and double the amps!)

That's an awful lot of "ergs" to be flowing through a few rusted bolts!

From what you say, the dash is isolated from the rest of the tractor, probably by years of rust and dirt.

The battery ground connects to the dash (if it's like my TO-35), so if it can't find a good earth through the bolts and brackets that hold the dash in place, it's going to earth through the oil line.

The oil line may not be able to adequately ground the starter.