Most likley scenario is that it is fitted but not working

Do you have a pair of relays fitted near the battery tray? and a spare rubber booted plug on the front loom with or without a small ally can like a bigger indicator can you got under the dash?

if so then thats all the cause of the hot switch

pull off the plugs on the relays one has 5 wires the other 4

on the 5 wire plug join socket 1 to socket 5 with a jumper( short wire with a lucar spade on eithet end. the numbers are on the base of the relays