Non Starting

[Chris]

The earth to the engine block goes via the change over relay from the second battery. If that connection is poor the car won't start. Connecting the neg of the same battery to the block simply replicates that connection. How else is the second battery is grounded?

It's the positive terminal you need think about.

 

[StarCruiser]

Yes, that Earth then gets connected to the + of the left hand battery, so creating the mid point. Which is why it must not be used as it changes from the negative to the positive/negative mid point.

Any connection from the far right terminal to engine shorts the right hand battery on starting.

 

[Chris]

All I can say is that it cured mine. Showed up the fault immediately. I don't recall saying run it like that, but in terms of fault detection it save me hours. Maybe jumping chassis to engine might have been better but would it have shown me the fault? I can't say now obvious because it's fixed.

It is an unecessariluy complicated system and I am pleased to be rid of it frankly.