Mercedes W123 300TD - Fuel Heater & Rogue Wire

A previous owner has fitted what I think is a fuel heater, powered by a live feed and relay, both water and fuel pass through it. The car is running hot and I working through bits to rectify this. Work done so far - coolant flush and thermostat change.
If I disconnect this I can eliminate the fact that this is doing something to my running temperature (just under 100 deg. C). It looks untidy anyway so it’s gonna go.
Secondly, the other live feed has been put through trunking and taped to my injector pipes. I haven’t touched it yet but at the other end an earth comes out! Obviously something not quite right there…