Hi Roling,

I think these older LP Trucks have GM IMPCO Engines. The faults seems to be an electrical issue, most likely a loom short. Combilift North America team can be contacted by email or phone. I can't add an email address here but it is service.usa followed by a @ and then Combilift.com.
Alternative go to the combilift web site and scroll to the bottom and select Technical Support.

Hope this helps.