289 M 1975 Peterbilt battery cable problem

Trace out where your main battery cables go to. Peterbilts typically run 2 main positives and 2 main grounds both of which should be connected terminate at the starter.

it appears as though your trying to hook one of the grounds on the positive.

Then one of the jumpers between batteries needs to jump across the positives. There’s no need for the jumpers to cross all three batteries but it won’t hurt to add them either. I’d just add positive. Jump cables between and pretty sure the blue sheath cable is gonna be a ground. But trace it to be sure.

 

Quick question. Is that a 12 volt system or does it have a series parallel switch?

 

Very nice little unit. What ever you do don’t just give it away. I agree 100 percent with what @Goodysnap posted above

 

You need to be sure. If it has a series parallel, it's designed for 6 volt batteries hooked up in series instead of parallel. Please make sure.

Nice truck

 

2nd the above, it's the right age to have had a series-parallel switch. With an SP switch it'll be 24 volt starting but a 12 volt system with 12 volt alternator. Definitely want to confirm if it has one.

I think they were normally four 6 volt batteries. However, I did use four 12 volt batteries on my KW with an SP switch and it seemed to work. Been so long I can't exactly remember how I connected them.