Hi there Brian,
I have spliced/soldered into the wiring of the original cargo bay light before the plug and then covered with heat shrink insulation. However if I was to do this again or recommend a way, I would simply purchase the socket fittings to plug into the standard plug and make a separate loom to go then to the factory light and my LED strip.
I could have splashed out and gone with the 50/50 LED which would have been brighter - would I recommend that - sure but I'm happy with the amount of Light we now have.
Hope that helps.
Thank you to all those who have contributed good ideas to this thread also.
PS Sorry for the delay