possibly main lighting switch when 6 and 7 way lighting switch not fitted

as attached

W2 coil must be earthed through metal body but check should hear it activate when 12 volts applied to W1

have you checked the door handle switch the glass should drops down to clear only , it think thinks the door is open and causing the problem

Have you confirmed that relay 9 is working ok ,have you battery voltage on c123-1 and c605-3 on the inertia switch to ground . and as mentioned by sierrafery the engine is not being immobilised

may help

did you check that your main relay was working before the fire starting

try attached

Assuming fuse 3 have you checked your headers for water damage and the reverse light and other item gauges etc fed by this fuse

try https://www.ebay.co.uk/itm/256413603714?gad_source=1&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338723872&toolid=20006&customid=dZcpDqgcAAAA3thFB2uUTOkHwRxFAAAAAA

try https://docs.rs-online.com/8dce/0900766b8148d932.pdf https://www.mudstuff.co.uk/collections/carling-switches

take a gander

as the immobilizer has been removed check your grounds as the unit removes some of these grounds when working

check the relevant headers for water ingress

what model of Leanardo unit this may help

just because it's new and shiny doesn't mean it's any good

not sure but may help

TRY https://www.gbsprings.co.uk/land-rover/

I would stick to your original plan as fitting in the battery box would render it to water ingress when wading and when running through melting snow unless your battery box is water tight (no battery anchor rods passing through the floor or unused bolt holes and gaps )

as the indicators work ok the ignition fed side of the hazard switch is working .where the brown fed from as this should have a battery feed for the hazard switch to work when pulled out,try taking a fused piece of cable from a known battery feed to the brown on the flasher relay and try...