Fuel gauge problems.

hello there,
Coming up with my second thread,
on my series the fuel gauge never doesn't work, i opened the panels ander my seat and discovered that the sender has two male spade terminals while only one wire is connected to only of those terminals. should there be another wire or is it normal? how can i trouble shoot if it the gauge that has gone wrong or the sender(exept from buying new ones immediatly )

Petrol vehicles just have a gauge, whilst diesels have a low fuel warning light as well., this means that a petrol sender has 1 terminal whilst a diesel has 2. It is not unusual to find petrols with a diesel sender unit, usually due to availability when replacement time came, and they work fine.
I know yours has a diesel in now, but it is the loom it was built with that matters.