You should be able to use the 18ACR plug in loom, then just join the two wires that aren't the earth on the 3AW to get the light working and fit the ring connector to the starter solenoid battery in terminal.
Just to clarify for an electrical dumb ass (me)
What is the 18ACR plug in loom ?
The 3AW is the round silver relay thingy in the drivers cubby bin on the door jamb ?
Please explain this bit you wrote
'and fit the ring connector to the starter solenoid battery in terminal '