Right...

Want to keep my wiring as neat and tidy as possible, so the shorter the runs, the better!

Mine is a mid-engined car, so where are the best places to mount:

a) The Battery
b) The ECU (if in engine bay, will it need heat shielding?)
c) The immobiliser

Ta!

[Edited on 19/1/09 by scootz]

a)Next to the starter motor
b)Behind the seat in the cabin
c)Behind a trim panel

Depends where you have room, but IMO

a) behind seats or if you are light at the front up there in the passenger footwell area.
b) On the cabin on the firewall, so behind the seats. Keeps it dry and cool while still close to the action. Most modern ECU's seem happy in the engine compartment though.
c) Somewhere it's hard to find/fiddle with. Behind the dash?

the ecu needs to be free from

1. heat
2. vibration
3. excess water (or any come to that)!
4. condensation
5. vibration
6. thieves!
7. securely mounted with rubber or foam blocks