Two ways you can do it - the billy bob basic way, which I did is to cut a couple of holes in each reverse light and add a pair of 501 bulbs in each, wire them into the reverse feed, then put red LED bulbs in the main holder and wire them into the fog feed.
The other way would be to use a red switchback LED, but you either need to mod the housing to accept a dual filament 1157 bulb or bodge the wiring for a single filament 1156 bulb.
Unfortunately I got rid of my Nova haynes manuals long ago so can't advise how to wire them up any more