you can get the original radiator re-cored from 3 t0 4 segment to increase cooling

take a gander the magic 8 https://www.hagerty.co.uk/articles/maintenance-and-gear/dvlas-dos-and-donts-the-risks-of-modifying-your-classic-car/#:~:text=Original%20suspension%2C%20axles%2C%20transmission%20and,have%20a%20Q%2Dplate%20fitted.

you could fit a modern 3 way cable operated valve that shut the flow off to the heater and allows it to circulate back through the flow and return pipes...

was the original coil you changed 6 volts if it was 12volt then no ballast resistor fitted unless the original was a engine V8.any images of the wire and coil in question

the ballast resistor usually has a white purple from starter motor which supplied 12volt to the 6volt coil after the ballast resistor on engine cranking and a ignition (white) feed through the ballast resistor to reduce the 12volt to 6 volt when engine running so the wire should run from the...

https://www.rangerovers.net/forums/range-rover-sport-l320.9/page-79 last but one item

ifo taken from Hella catalogue ,your starter has a pre-engage solenoid so should not draw a large current have you tried attaching separate earth wire to the relay to eliminate the alarm ECU the B/O wire when it's a none starter 4-PIN SOLID STATE RELAY Normally Open Relay (Solid State /...

think it's related

I would lose the post code are the battery's fully charged, have you checked the battery earth connection on the main battery

no water in trailer socket or caravan plug check link 5 in engine fuse box as this feeds both seats and fuse 34 to items in the body control module .Also check engine fuse box for corrosion or water ingress if seat power is a intermittent loss

Colour

any wet carpet events ,sun roof drain heater matrix leaks check header 289 ,it's a two part header an can be separated to check for good connections and allows you to check each indicator in the circuit and the two relays

see

check headers

no EBAY in general it's becoming a Chinese wholesaler buy cheap sell high with the union flag and put the Land rover or classic in front and the greed escalate to another level

have you checked for water ingress on sunroof module

the connector is basically a male and female connector try https://www.automotiveconnectors.com/20-way-sumitomo-hm-splice-female-23mm090-blue.html you can find them on EBAY but some of the prices are greedy, to remove and replace the crimps just a matter of bending the retaining tab back but...

Hella ,Bosch and other do Solid State bladed Relay but they are not cheap but still prone to crappy spade relay bases ,on my series one I fitted a 6 way relay base form a LDV van which has the spring contact connections .the early SSR would switch at 3 volts upwards flat battery or not so...

the problem with the relay could be the actual relay holder at the end of the day they are just spade connections and loosen over time and the more you wiggle them the looser they get as they are retained by a simple barb on the back of the spade simply bent outwards to stop the connection...

on my 1957 series 1 the glow plug have been replaced with 12 volt type ,resistor removed and the relay is mounted on the bulkhead behind the speedo panel with cable from relay coil supply to the warning light ,safe from water ingress and protected by a 50amp maxi fuse on inner wing panel just...