ok i am going to have another go at this
do i HAVE to put the audiable relay on?????
Yes its a legal requirment, unless you place a visible flasher led or similar that only flashes when towing electrics are plugged in.
The other thing is the extra relay takes the strain of adding extra lights to your cars existing flasher relay.
Or you just simply uprade the existing relay to higher amp one.
If you dont use additional relays you run the risk of overloading the cars own one.
Also note if your car runs a multi-plex wiring system or cam bus system you may need a bypass relay to avoid currupting the cars own systems ( expensive).
Usually audi, BMW , Jag, and alot of modern cars with bulb failure systems.
As a genreal rule of thumb if you remove a bulb and the car does not tell about it then you dont have that system.
As to scotchlocks ( the blue snap connectors) it spend upon the make 3M etc.
Cheap ones are crap!
You different colours for diffrent diameter cables, red being smaller than blue nornally right up to the big cream ones used on ignition wiring.
the main problem people have with these is that they sometimes dont cut through the wire casing properly and therfore give an intermitent connection.
soldering is he best way to be sure.
To test your wring colours as to which wire runs to what simply unplug the multi connector to your rear lights cluster and use a 12v screwdriver with a bulb in it ( or make one up with a car bulb and some wire, croc clip etc ).
then one end to a good earth on the bodywork and try the indicators, road lights brakes etc until you have identified all the required wires.
Can get a little more complicated with more modern cars using seperate or extra sidelight bulbs as well as stop/tail bulbs.
If you are only towing a small trailer dont bother with the fog light wire ( blue) as its not needed , but larger trailers , caravans etc do.
for more info try towsures website.
I have using them for over 20 years for towbars on a trade account.
they trade on Ebay as discount towing.
If you need any futher advide then PM me and i wil help you .
I'm out all day today but in this evening.