On my 2006 CR-V, I found the harness runs behind the right-hand trim panel in the rear cargo area. There is a connector with about 20 wires located right above the rear wheel housing. On the rear side of that connector, I probed wires until I found the ones I wanted (tail lights, brake lights, left turn, right turn). I cut those (one at a time, of course) and installed the diodes there.
The wiring kit I used had four diodes, each having two inputs and one output. To install the diodes, I had to cut the Honda wire, strip both cut ends and crimp on a spade plug on each end. The spade plugs onto the diode -- the end nearest the tail light, for example, plugs onto the output side of the diode. The wire nearest the harness goes to one of the input blades on a diode. I also brought the wire harness from the motor home to that same location, and stripped/crimped a spade lug on that wire. It plugs onto the other input spade on the diode.
The diode isolates the MH harness from the car harness. Input from the MH travels through the diode to the light, but doesn't feedback into the auto harness. If you're using the toad, its normal power feeds thru the diode and illuminates the lights.
This was somewhat of a pain to do because I had to hunt for the right place to connect everything. Maybe I could have made the connections inside the tail light housings, but maybe not. I had removed the tail light housings, but it just didn't look like there was good working room. Removing those trim panels is not that difficult. I started on the left side, as someone had told me that his CR-V harness was on that side. That may be the case with yours as well. But I didn't find connections to all the lights there; I had to remove the right-hand panel.
The hardest part of my entire job was getting the four-wire harness thru the car's firewall; once I got that done, I felt like I had really accomplished something.
USAF, Retired (1962 - 1983)
2000 Itasca Horizon 36LD, 300 Cat
2006 Honda CR-V Toad