Thanks. As Roger says you'll need to stop the DRLs which come on with the ignition feeding the rear position lights through the factory wiring which connects them to the front position lights. And you can do it • With diodes, as above.
• With a changeover relay in the feed to the DRLs so that they can be powered either by the new ignition circuit or by the factory sidelight circuit.
• With some sort of relay in the feed or earth to the rear position lights. (It would be amusing to isolate their earth with a relay from the new DRL circuit!) I can't see any advantage in the third of these. Experts, please: What are the advantages and disadvantages of diodes and a changeover relay? If diodes are preferable what's the specification? NB: If you run a new circuit remember that it might need a new or differently rated fuse. Jonathan