14vdc to 28vdc up converter
OK, I did the same as to what you want to do. The 14v units are more in demand and that makes them more expensive, so I will give the straight scoop.
I have taken a 14v unit apart and looked at the guts with a maintenance manual.
First, the 28v units will use 28v light, they will work, but will be dimmer than the 14v lights.
The relays are 28v, and will switch over.
So they bottom line is, it will work. Mine did, but all I wanted was the button switches to get my KLN90 to work and the lights to come on.
Anyway, it will be a real pain to switch the lights and relays out if you need them, so I installed the following unit which is cheaper in compare to others. Since you are just going to run the lights and relays, the current draw is very low.
They are made in Germany so you know the quality is good. I am happy with the one I installed.
http://www.jaycar.us/productView.asp?ID=AA0264&CATID=83&form=CAT2&SUBCATID=1002#12
Good luck, and if you need any more info, PM me and I will see if I can help.
Brian