TL99 is your 12v lead to the PPD/cab and alt 12V terminal. It should be connected to the end of the 4 terminal zigzag. BT2 - is as good as anywhere, but it could be connected to any of the 4 terminals that the zigzag connects to(same point electrically)
TL48 is your ground and should run to the instrunment shunt(used to measure current).
Unfortunately hooked up the way you described, you have been feeding 24V into your 12V circuit, so hopefully you didn’t kill anything...
A disconnect on the ground lead is one way to electrically isolate the batteries To eliminate vehicle caused discharges. These trucks have a small 12V discharge/vampire load caused by the transmission which will over time discharge the outer-most pair of batteries(0-12V). Using that switch will stop that discharge.
soap box time! I would highly recommend you drop the bank down to just 2 batteries like is pictured above. The folks who put this truck together to meet a particular milspec made a very large error pairing this size of a battery bank with this small an alternator. If the batteries are allowed to discharge, with such a small alt, it takes a very long run time to charge them. If you don’t run the truck enough hours to fully charge it, or use a maintenance charge regularly you damage the batteries. Low state of charge is the biggest overall killer of lead-acid batteries, and bad batts kill alternators… To add to this, most of the electrical load is on the 12V side, so if the lights are on, the 12V pair(outer most batteries) takes a very long time to recharge. It is a vicious circle and the reason these A0 trucks have so many power issues.
Their error is proven by the later changes they made to the A1/A1R by adding the disconnect relays and the LBCD, which disconnects the batteries from an overloaded alternator and puts them on a trickle charge to save the alt. They went ahead and put in a 260A alt on the A1R, which was really necessary as AGM batteries became the norm and they make the overload problem twice as bad because they can draw more current during the charge. AGM batts in an A0 is a recipe for alt failure if you don’t pay close attention to them And keep them fully charged.
For the power equipment that uses the 3116 or 3126 engine, cat specced a pair of group 31 batteries @ 100AH capacity. The 240AH specced battery is gross overkill… halving it to 2 batts @ 120AH is closer to what cat specs and your alt will thank you in the long run…
