Cyrix ct wiring

[Welshclimber]

I’m installing a cyrix ct and removing the old relay switch. I have attached the wiring diagram for it. I’ve done most of the wiring but unsure whether there should be a negative cable between the two batteries or if it’s just showing that they both need to go to ground? If anyone can shed some light on it please that would be great!

[Cecil]

Grounding the negatives to the chassis with good clean connections,perhaps corrosion protected with a bit of petroleum jelly would be best. I don’t think the wiring instructions intend you to link negative copper cables to the alternator or starter motor either. Linking the battery negatives with copper cable would be the way to go if the starter battery and the leisure battery were adjacent to each other but that is unlikely in a t25.
Fit the fuses as close to the battery positive terminal as practicable . Also consider adding an extra 120 amp fuse in the positive cable between the starter battery and the relay ,again close to the battery.
I like the start assist function!

[Oldiebut goodie]

That diagram is meant for boats - they don't have a chassis to use as a ground therefore they have to run negative cables.

[Welshclimber]

Thanks both, that’s really helpful. Will also get another 120a fuse as that makes sense to protect the wire that side too.