Cable joints.

[overherebc]

I have to connect wires, only two, pos and neg, under the car at the rear. I obviously don't want to use the traditional local method of twist together and cover in sellotape or similar.

Is there such a thing here as a good joint unit that would be road spray proof? Like image.

Can't re-route without stripping out the whole interior.

[Kwasaki]

An auto-electrical shop will have what you want or a motorcycle shop. 

[fredob43]

Strip wires Solder them together and use shrink wrap. Before putting them in a waterproof flexy tube. Attached with cable ties. That's what they seem to do here. Worked for12 years without a problem on my old Vigo.   

[overherebc]

Search over found a couple.

??