For the trailer warning light you will need a four pin relay see hereLand Rover Defender LED Flasher Unit 4 Pin Relay like Wipac WFL7LED Adjustable.
Valeo New Alternator Replacement 12V Fits Land Rover Defender Range Rover BV PSH
Land Rover Defender Discovery 1 Range Rover Classic Low Note Horn 12v - YEB10027
12V Starter Motor Solenoid For Land Rover Defender Discovery Range Rover Vogue
High Note 12v Horn for Land Rover Defender TD5 TDCi PUMA YEB500140
12V Starter Solenoid Switch for Land Rover Defender L316 110 / 127 LDH Discovery
Genuine Lucas SFB191 12v 4 Pin Flasher Unit Relay (PRC8876 Land Rover Defender)
