The 2 yellow wires both connect to a large rod within the machine with lots of steel wires coming out of it (look almost like bent paper clips!). In the below photo the yellow wires are inside that black insulation
We recently bought one of these from a farm sale auction and found it didn't work when we got it home.
First we cleaned it up as well as contacted SIP for an operator's manual and a schematic.
Found parts for the torch weren't readily available here in the UK so sourced some from Australia.
Couldn't see any obvious reason for it not working.
Googled for problems and found this thread and even though I had checked the obvious switch in the torch handle I opened the torch up again and found that the micro-switch was goosed. Having broken out the soldering iron I soon had this bypassed and the machine burst in to life.
I'll attach the schematic in case it is of any use to others.