Hi all,
It's been a couple years since I've poked in here as the truck has suburban has been relegated to occasional use status and was also running good while doing it. Until now, which brings me back!

Something's been up for a while but it was ignorable (hah!) until now. OEM voltmeter in the dash has been reading low, I've had a long-term parasitic drain (solved with battery disconnects), and occasionally starting would be sluggish. Well this last week while doing a dump run in the summer heat this gremlin hatched into it's final form: a dead truck. At the transfer station (city dump). At closing time.

When I say dead I mean no power to the cab. After 15 minutes of grovelling on the dump floor (an automotive low point, for sure) and under the hood, with annoyed attendants pacing around as if that would help, I finally got it to fire back up. What I did was pull the two + wires off the alternator, rip off the connectors, and direct macguyver splice the two together to insure a solid new connection, while wiggling the seemingly tight battery connection. With each new attempt the lights would come back on, I'd go to start, and the starter engagement would kill everything. Which leads me to believe that the electrical load is the culprit.

The connections between the batteries and from battery to main + out is good and recently fiddled with. Ohm meter shows great battery voltage, a low resistance ground. So I'm thinking it's power towards or ground away from the cab that is the issue. That would explain the no lights total death and the persistently low cabin volt meter in the dash. And here's where i need help.

It appears the cab and everything in it is fed by the one red wire coming off the alternator. Is this true? Any idea how that wire is routed?

What is the ground path from the cabin electrics back to the frame/batteries?