Sprinter negative battery connection

[Sprintervanman]

Hi all, i have an accident damage 2016 sprinter , have changed all to do with the air bags also changed live battery terminal, do i need to change the neutral terminal lead aswell? As van still wont start, what are the purpose of the red and blue /white cable which plug in to it? Tia

 

[cheddar]

The one you picture on the negative terminal senses current, for energy management purposes only, does not cut power.
The one on the positive terminal is the one that disconnects starter/alternator circuits in a hard impact, but there is a distribution box near the battery that can isolate other supplies too following impact.

 

[Sprintervanman]

Diagnostics machine comes up with one fault, no output at terminal 50??

 

[cheddar]

Have you been through all the fuses?