I'm putting my newly acquired '88 back together. When I fixed the long dormant foot brake light switch I tested all the lights to make sure they worked. Today I replaced the damaged clutch and front brake levers with some questionable quality new ones, and again attempted to check the lights. Now nothing works. The battery is up and there is power to three of the four wires to the relay above the right shock, and to a single red wire heading up under the tank.  No power to the key switch or anywhere else.  So are there fuses somewhere? The only wires I unplugged were those from the magneto. Plus the ones on the new clutch and brake levers. I didn't have the tank off - is there anything under it I should check? At this point I'm stumped. While eating dinner I had a thought - the first time I tested the lights I had the bike on a stand. This time it was on the sidestand. So I ran out to the shop, stood it up, and folded the sidestand. Still nothing. Rats.

Ah yes, the one I thought was a relay, since it says "relay" on it.  One fuse was blown and its replacement blew immediately. So any suggestion where to look next? I'm going to unplug both the clutch and front brake switches since they are the only wiring I had fooled with. But have to go get more fuses first.  I read somewhere that the decomp system can cause electrical problems. I have no idea how to test that.

I unplugged the two switches I had been messing with and replaced the fuse, turned the key and it blew again. So next I will re-check the battery connections and every other wire I touched. I downloaded the wiring diagram so that should help. Any other suggestions would be appreciated.

As I just posted under The Cafe, I removed the seat and tank, and unplugged every connection I could find.  With a fresh fuse in place, I started plugging them back in until it popped again.  It was the plug under the tank for the RH handlebar switches.  I thought I had narrowed it down until I noticed 7 wires at the plug but only 6 at the switches, and wires having current flow that shouldn't.  After slicing open the sheathing I found that 3 wires are joined together inside the sheathing, which therefore sends current from the orange wire back upline to the plug and who knows where beyond that.  This is making it much more difficult to solve since the wiring diagram I downloaded here doesn't show anything like that, or match the wire colors I'm finding.  And it is all original, unmodified wiring.

Good advice, but I think I found the problem. My plan of reconnecting plugs until the fuse blows had a flaw - if I connected the problem plug and then one upstream, the latter would appear to be the faulty circuit. So I started over in a different pattern. This time the lead to the LH grip switches was the fault, and since the horn and signal switches are not energized at rest, I figured out it was more likely in the headlight/front signal circuit. I unplugged the headlight and both signals and then plugged them back one at a time until the RH signal blew the fuse. When I got the bike the RH signal was very loose so naturally I tightened up the attaching screw.  It was still loose so I cranked on it some more. But apparently a previous owner had used screws that were too long and I ran it through the wires.  Lesson learned, and I will be checking the other side too.
As for the new clutch and brake controls, I needed a new brake reservoir so ordered a matching pair, but they are cheesy Chinese quality. The wires are a little short to fit and the brake ones were mangled anyway, so I will be extending them. Probably not the best plan but it will do for now.