It shouldn't matter which place you tie in. I think it's typically to the starter solenoid post that the factory tied it in. IF you are losing power through the day and you are not using power (i.e. gp's, starting, etc.) then I would start looking for a draw. If you are starting and using the truck through the day and it's getting progressivly weaker, you are not charging. Have you tried running a new cable from the charging post on the alternator to the solenoid? Typically there is a fusible link there I think. If it's bad, it wouldn't charge. As a quick check, you can carefully, hook a jumper cable to the battery hot post and the charging post of the alternator (don't let it touch anything) and see if the voltage changes. You really should be at like 14+ with it running and charging after a start. If the alternators are testing good, then it's got to be something in the wiring to them that is either telling it not to charge or not letting it charge. Alternators read the system voltage and adjust to charge accordingly so that you don't overcharge the batteries. It will only supply what is needed so if it can't tell anything is needed, it won't charge. The other thing you can do is by-pass the lt gr/red wire and tie it to the battery + to simulate the key on power. I really don't know what else it can be. If the alt is good, its key on voltage in, power out. If all the wires are connected correctly and tested to be good, then I'm completely at a loss.