carringB - do you mean "main chassis" battery or "house" battery - did all SMB West rigs come with one ? What does it look like (photo) ?
Your knowledge level is SO MUCH appreciated - as is ALL senior members and others who unselfishly answer questions - I personally apologize for my lack of knowledge mechanically and electrically ! I played too much golf and tennis growing up, I guess ??
Yup^ That’s the one. The upper one labeled starter relay. It’s the same for 7.3L PSDs. I’m not sure about 6.0’s.
Everybody should know where this is, because it’s the most common no-crank fault on our vans (and probably has resulted in MANY unnecessary starter replacements). Mine goes out every 100,000 miles. I carry a spare. Just rolled over 500,000 some I’m due for another….