I have been thinking about an easy way to do this modification for a while
and finally got around to putting something together tonight.  Here is a
quick prototype of what I think would be a simple and very secure connection
solution:

https://sites.google.com/site/vanagonheadlightrelays/home/12vsplitter

I have been using the male 1/4" tab method in my '87 Wolfsburg and it has
worked fairly well outside of a couple times when it wiggled loose on bumpy
roads killing the radio etc.  Losing the radio until my next stop is no
biggie, but if the wire worked its way out and grounded against something it
could make for some sparks and a much bigger pain in the butt..