Got No electricity... No power to start, no On the dash,

I have a second truck that I've been babysitting until I clear up a few things with it and today I went to move it to cut my grass. Well there was no power at all. Nothing on the dash lit up, no air buzzers, etc... I was gone for about 2 weeks and had it running warm before I left...

I had to leave the house to go finish this load I'm under but I was looking for some pointers or advice on troubleshooting... I didn't leave any lights on or anything like that... Though once I get it back running I need to make sure there wasn't a light under the bunk or something that may have been on...

My plan when I get back is to test the voltage at the batteries with the key on... 2nd, take the batteries out & take them to NAPA and load test them... Check for grounding issues... I know there's an oil leak @ the cam followers that is leaking basically right over a stud on the frame that is used for grounding 4 or 5 wires... ((This will be corrected b4 the truck hits the road)) ...But I just drove the truck 1500 miles home no problem about a month ago...

Any tips or pointers would be greatly appreciated. Thanks in advance and safe trails

 

I see... So when I do this, I should hook up the cables directly to the battery right? And If so, which battery would be the best to hook onto

 

10-4. Yea it's an N-14 celect but only 3 batteries on this one.

 

Okay so I cleaned everything up real good, couldn't seem to find my multi meter. But I hooked up jumper cables and charged them from my other truck. Well I got the lights on the dash to come back on... I've been charging the batteries for a little over 30 minutes now with the truck idling around 1100 rpm.... It's clicking but not really trying to start... It has made some vibration like it was wanting to start turning over.../// Is it that the batteries aren't charged up enough?? I tried to start it about 15 times and I didn't want to burn out the starter... I was going to tap on the starter but I'm new to the N-14 and don't know exactly which one the starter is. I see the a/c compressor, air compressor, power steering pump, alternator on the passenger side, ...

Any more pointers or tips?