i am changing the engine in my 318 e36 to a 325 engine

how do i go about relocating the battery to the boot?

i know i will have to run a new +ve cable but where the battery origonaly joins there are 3 wires

what is the best way to join them?

I would look into a battery relocation kit that the 240SX guys use. The kits come with wiring, connectors, and a battery box with tie downs. I never realized that the 318's had the batteries under the hood.

summitracing.com sells battery relocation kits also. The plastic ones are pretty shitty cause the plastic breaks, so go with one of their other ones. I got the plastic one for Christmas one year and broke the damn thing trying to install it. I hope the other kind they have is a bit better quality but I don't know. :dunno