Why would the manufacturer use thicker wires?

Hi everyone!

I rewired my car in January prior to this course. I will do it again more professionally soon but I noticed something. I have the Haynes book for my Vectra B and I used its wiring diagram for the job. Yesterday out of curiosity I checked a lot of resistance of different sensors, actuators and such. The readings were near what I learnt in the course however the wires were thicker ones than what were recommended in the course. I am sure that because of the resistance measures we can use thinner wires but then the question arises: why did the manufacturer use thicker ones if they are obviously more expensive?

I would appreciate any insight!

Heavier gauge wiring adds weight and expense - both things manufacturers try and avoid, but sometimes there are issues such as current or voltage drop limits, that require the heavier gauge wiring. It may also be to ensure the mechanical strength of the wires are up to the vibration, etc, loads they will be subject to.

Exactly which are you referring to?

Thanks for replying!

A lot of them actually. For example my injectors have 1 mm^2 wires so 17 AWG to them even though I measured their resistance and it is around 15 Ω. So 22 AWG would be more than sufficient. But there are a lot of examples. Inlet manifold solenoid valve, EGR solenoid valve, fuel tank ventilation valve, idle speed actuator have 0.75-1-1.5 mm^2 wires. I measured their resistance as well and I got bigger numbers so totally don't see why. Ignition coil has two 1.5 mm^2 and a 2.5 mm^2. Strange. I mean to be exact I needed 8 m of 0.5 mm^2, 29 m of 0.75 mm^2, 16 m of 1 mm^2, 15 m of 1.5 mm^2, 3.1 m of 2.5 mm^2 and 0.25 m of 4 mm^2 wire to make my engine harness. I made some modification of some of the trajectories so it is better organised but it doesn't even have 22 AWG wire in it (20 AWG being the smallest) even though I learnt we use that a lot and the actual resistance measurements that would suggest smaller wires.