Putting in new lithium for all accessories. Is there no negative wire?

[CHECrappie]

2013 Triton 19XS

going to move all accessories to a lithium battery. On starting battery there are 2 positive wires but only one negative. One of the positives goes to the motor as well as the negative. The other positive wire goes to a switch/breaker that kills everything from the battery. However, there is no matching size negative. There are positive and negatives for the bilge and some other accessories on the starting battery but they’re all small gauge wire. Am I missing something?

Should I tie the negative if the lithium to the negative of the starting battery?

[EricTR21]

I think there should be a negative going to negative bus bar mine is near the top cap of the starboard side of the battery compartment.