05-09-13, 09:39 AM
As always when there are electrical problems, it's well worth checking the connectors make decent contact and the harness hasn't chafed through anywhere, but it's hard to see how an external short circuit could cause the ignition unit to get excessively hot when the engine runs normally.
If the supply volts are OK then it's overheating is most likely due to an internal failure… though it would be unusual, they're extremely reliable.
I'd jump at red98's offer, substitution is the easiest way to prove whether the ignition box is the culprit.