OK. If the leads are getting hot the battery may be OK but you have a short somewhere? The switch or solenoid may also be faulty.
I'm not familiar with that switch so can't tell you if it is correctly wired or not, but it doesn't "look" right? The white wire is power into the switch and red wire is power back to the solenoid. One would think
the white power in wire should probably go to the switch central position (if that is the power in position?) - but appears to go to the accessory/on position??? Don't change it as I may be completely incorrect?
Where does the red wire on the switch central position go to?
Can you look closely at the black bakelite back on the switch and see if there are any markings on it? My guess it has three positions - "off", "accessory/on" and "start", or maybe four positions "off", "accessory", "on" and "start"?
If you have a multimeter set to continuity, you could disconnect the switch and check it's internal circuitry?
I Googled "wiring diagram universal ignition switch" and came up with a number of sites but THIS
The reason it is hard to help is that your TEA20 never had that switch from new and did not use a starter solenoid. Originally, the starter was engaged by placing the gear lever - "shifter" - into the "S" position, which activates a mechanical switch in the bell housing, behind the engine. Often a solenoid is fitted because often the mechanical switch appears not to work when all it needs is adjustment - it is held in by four screws and adjusts forwards and backwards.
Is the battery ground/earth still connected to the back of the dash or has it been moved to one of the starter bolts? On these old tractors, the dash is a very poor earth/ground and the lead should be moved?
The Lucas starter on your tractor does not give many problems. You could test run it in a vice, by jumpering leads onto the case (ground) and the terminal on the back end of the starter. There is a dust cover around the back of the starter, lossen the screw, remove and you will see the two spring loaded brushes and commutator. The brushes should have "meat" on them - not worn out - and commutator should be bright and clean. An auto electrician should be able to test it for you, for a few dollars.
Sorry about the vague reply, but I am not familiar with that ignition switch. If the black bakelite has any markings on it, post here and I'll see if I can work it out - or someone else may know. I will check my 1966 Jaguar XKE later today as I suspect it has a similar switch, although it has a separate starter button.
The Messiah of Fergusons, John (UK) may be familiar with that switch, as it was common on British cars of the 1950s and 1960s.
I wonder how a TEA20 got to Knoxville? :D
Bob in Oz
P.S. That is a 12 volt system with 12 volt battery? What is the tractor serial number? If in doubt, the 6 volt and 12 volt Lucas starters are different (6 volt has a nose cone) and I know the Lucas 12 volt starter has "12V" stamped into the case. This post was edited by Bob (Aust) at 12:40:47 10/09/10 7 times.