I did this mod a few months ago but I finally got the pictures off my camera and finished up the Visio diagram for the circuit so I figured I would share.
I installed a Harman Kardon Drive+Play for my iPod a while back and the location of the stock hazard switch was the perfect place to put the control knob. Only problem, what to do with the hazard switch? I had hoped it was a simple SPST switch that controlled the blinker relay but why would Honda design something that simple when they could use a TPDT (that's right, tripple pole double throw) switch instead? You can exactally pick these up at Radio Shack so I couldn't just buy a simple switch and wire the stock harness to it. I also didn't want to reuse the stock switch because I've been dying to get one of those big red "aircraft" switches on my dash. My only option was to find a TPDT relay and wire it up with a simple SPST switch controlling the coil. Hence, this contraption.
Note the in-line fuse on the power lead going to the switch. The circuit I tapped for the power is already fused at 15A but I wanted a seperate fuse for the relay coil. Since the coil draws about 0.2A I figured I was safe with a 5A fuse. This way if the coil or switch shorts it will blow the 5A fuse before it blows the 15A fuse under the hood.
Based on the pin outs given in the Service Manual (that green thing the circuit is sitting on) I was able to design this circuit:
Which is based on a very badly hand-drawn piece of crap...
So the fabrication was pretty easy, I just used 16ga wire for all the leads with 3/8" female spade connectors on the ends to connect to the relay and switch. I did run into two snags. First, I purchased a TPST relay by accident but luckly it still had the contacts for the second throw so I was able to solder a lead directly to the contact. Second, hooking into the factory harness was a challenge because the male spade connectors needed to be about 1/8" which is, again, not something you can buy at Radio Shack. I ended up using 1/4" spades and grinding off half their width with a Dremel.
Here's a pic of the contacts on the relay. This gives you the pin numbers used on the diagram above
I think the whole thing too me about 2-3 hours not including the time it took to track down the relay. The only hard part was getting my handmade 1/8" spades to stay in the factory harness. It took some creative electrical taping but I managed to get something relatively secure.