Building trailerhitch relais box, some Q's.

Hi fellows.

Due to not being able to use the cheap American trailer-hitch boxes (too little wires), and them being bloody expensive here, I'm building my own.

Supposedly the Prius doesn't have a wining canbus and can support the extra lights in parallel to the normal brake/indicator/etc. lights, but it doesn't feel right.
I tried designing them with electronics, but you will always have a voltagedrop with normal transistors and fets also are tricky with such 'low' voltages.

So decided on relais. they draw 30mA, so it's peanuts.

My questions:
- is it correct we have 2 fog-lights? Are they both on the same circuit and fuse? Our trailer-hitch sockets often have an auto-disconnect when a plug is jammed in there, so you're not constantly staring into the glow of the foglights reflecting of off the trailer. But I'll have to cut both fog-light-power-feeds and parallel them through this switch and back to the lights.
- can I find an accessory wire somewhere in the rear? If I don't need the 6th relais for the foglights, I'm reserving it for a switched power which should only come ON when the car is in ready-mode. Even considering adding a 30 second delay so it doesn't interfere with the start-up current during getting "Ready".

 

No, I don't *need* the accessory, but I like making it fancy I have a 13 pole socket and it would be a waste only to use half (we have standardized 7 and 13 pin plugs, I happened to run into this cheap 13 pin socket and my other car is also 13 pin)
BTW, the +12V would be fused with 20A and the accessory with an extra 10A thermal, resetable fuse.

BTW, my Volvo has (guestimate) ~23AWG wiring for the 60W headlights so wouldn't even consider paralleling anything on that, but I think the Prius wiring has some more 'headroom'.But still doesn't feel right to add a ~50W draw without any upgrade on wiring/fusing.

Just worked on it today, so it's almost done (wiring it up will be another matter though). Will post a pic shortly incase anyone's interested of a pic of 6 relays in a box

 

Thanks. I wish... But we have separate indicators, whereas the indicators in the US are the same as the brakelights, correct? So I would not be able to use that box, sadly enough (we have 5 wires + 1 ground in our standard plug). I also searched for the pass-through connectors and even mailed EVnut about the connectors he used (link) but I cannot get hold of the connectors, nor did he know where to get them now.

So that's why I started this project and am, sadly enough, forced to hack into the existing wiring. Not willingly, but I see no alternative (but am open to ideas!!!)

I would very much like to know HOW they did it though, seeing the size of the box, I think they used electronics instead of relays, so they seem not to have my (perceived) problem of voltage-drop to the lights.