Can't see how the body can be acting as the positive supply though, but don't worry about it.
Dont worry too much about that, I think it was either some older vehicles that had a positive earth or might have been older military vehicles. Think its safe to say vehicles today are all negative earths. Still it's always safer to check with a meter if your going to wire something up to your vehicle esp if wiring it to an existing wire or switch and esp as some vehicle manufactures dont stick to normal wiring colour codes i.e Red wire does not always a positive feed and Black is not always a negative. I have a Black wire coming off my door switches but I have no idea if its a negative or a positive been too busy to put a meter across it.
Yeah I'm using a 2G Giff Gaff sim, but think its my Virgin network thats causing the delay as I can see when my Caravan alarm transmits a text, not all are received straight away, the delay varies quite alot. Might finish wiring up the GPS this weekend and give it test run, just depends on weather and other jobs I'm trying to finish