dead in the water......73 cb500 77 cb550 engine swap

so the other day i ended up getting the engine to fire on the swap i did around christmas time. dropped a 550 engine into a 500 frame. it ran multiple times for a minute or so each just to get the oil to lubricate the upper end after a rebuild. it was 40 degrees or so the other day so i decided to do it again and everything seemed to work properly (electrical and mechanical). then it just died. i cant get any juice to anything on the bike. the battery tests out good and when put on a charger instantly kicks over to float charging. sitting steady at around 12.3 volts. i replaced all the fuses and still no power or ignition. is there something that i could have fried in the process of running the bike? i took my multimeter to the main fuse and seem to be getting power to the fuse itself so it is somewhere after the main fuse in the system. any information would be helpful at this point. i would go out to the garage and do a full test with the multimeter but its only three degrees out currently and my hands dont want to work properly in this weather. wish i could just bring her into the livingroom to work!!!!