Just wondering how the OP went with the headlight issue... just had fun making a plug in relay system for mine as my switch kept melting and I found the reason why. Some @#$$ didn't wire one of the headlight plugs properly when it was changed so when high beam was applied, both high and low beams were on hence the dim light. Plus the wiring wasn't designed for a 120W globe so the headlight went dim. Now all the headlights work brilliantly and now I can drive at night with the high beams!
WIth DMM's, I'm not affraid of them I have around 3 different types and use them very often.. Ony time I use them on a car is to check chraging voltage..and that's about it. Many good autoelecs I have chatted to swear by the good oll testlight. When I was doing my emergency breakdown service job, test light was always in my hand with any electrical issue. Test lights can show you if there is any form of bad ground or low wattage...the globe wasn't bright! If you know how to use a tool properly, in the right hands its a very powerful diagnostic tool. DMM's have their place in electronics without a doubt... but when you are dealing with just 12V, test ligt for me works wonders.