Hey I’m helping a friend with his gem. It’s a 2002 Gem. It has the upgraded DC to DC converter on it. He has no 12v output. No lights, No horn,No wipers. Basically all 12v acessories are not working. When I checked the voltage in the colored wire (in the photo) I was getting 40+ volts. It was my understand this was the 12 output. One other strange fact. When he switches the headlights and the wipers ON the car will NOT run. Any help or advice would be great.
P.S all the fuses are good and the grounds are good.
Sounds like someone definitely made some unintentional wiring changes. I tried to find a wiring diagram for you, which is what you really need. You would surely find that in the service manual. But I couldn’t find that either. The only thing I could find was someone who was selling service manuals online.
Here is an eBay link, and here is another possible source.
Perhaps if someone owns one of these manuals, they can scan in the wiring diagram and share it? 
Grant
Email me I have a service manual on PDF File is too big to post here
Rodney
rodneyadiehl@aol.com