M60A3MG

On Mine whomever installed the Plow and front grille jumper cable system wired them to the Aux Battery probably cause it was closer. The PDF with the schematic was helpful. I believe my fuse holder is on top of the main battery though. I will check out replacing the relay next

I already replaced the solenoid, I didn't know it was grounding where it is bolted to chasis, Also The 2 small wires the connect to solenoid, will just one be positive or both especially if it is grounded through the mounting? I prefer to keep the solenoid as I like the idea that if I run down the Aux battery , I still have power on the primary to start. I have been looking for schematics but no luck,

The Voltages are rounded off

I have a 2011 Sierra 2500 HD with 6.0L. I bought it from the original owner. It has the Factory Dual Battery setup. I started noticing a problem with My snowplow and then the external Jumper cables, Both of which are connected to the Secondary Battery. I had Replaced Both batteries with New ones thinking one of the batteries were older and I just like to make sure I always have a good battery. a couple months after replacing them I noticed a problem I was having with a Ham Radio that I just ran a power line from the secondary battery. I ended up putting a meter on the second battery and got about 10 Volts. The Primary is 12V when sitting and 14V when the engine is running. So traced the wire from the primary to the secondary and identified the solenoid / coil "part number 12135194" that keeps the battery separate when the truck is not running so the primary won't get drained. On the solenoid I have 14V on the primary battery side and 10V on the secondary side with engine running. This made me believe the solenoid was bad and not opening to allow the 14V to pass through to the secondary. Only $60 so not bad. Problem is I still don't get the 14V being passed through the solenoid. The next part I'm looking at is a Relay 21997407 Am I barking up the wrong tree or Is there something I should check first??