My old RV has nice little LED bulbs installed in all the 12V dome lights. They are a little bit more money but way cheaper than changing the entire dome light to LED. They also work in the tail lights!
I pulled a few out and replaced the 12V bulbs with them in the 12V dome lights in my ....They don't work! Why would they work on my 12 volt lights in an RV and not on the 12v lights in a mac? let's see somebody answer this one!
Yep. I don't know why, but the lights in the Mac are always wired backwards from what you'd expect in a car or RV, so although incandescent bulbs work fine, when using LED's you need to reverse the polarity.
As stated, most likely polarity is backwards. Mac workers didn't have to concern themselves with polarity on incandescent bulbs.
I have found some LEDs that work both directions. One is in my anchor light and I had to install an actual Diode to use it in my reverse polarity mast steaming/anchor scheme.
....They don't work! 
Why would they work on my 12 volt lights in an RV and not on the 12v lights in a mac? let's see somebody answer this one!
