I've heard that connecting the positive lead first can lead to shock if you somehow ground yourself before hooking up the negative side, i. e. touching the frame as you lean over the fender. If I'm wrong, then what is the proper way to replace and reconnect the batteries in a dual battery set up?
Crunch,
A twelve volt system won't shock you. You can lick your fingers and touch both terminals on a battery and feel nothing.
The factory service manual for my 1995 truck doesn't give a procedure for changing the dual batteries in a diesel, but here's my procedure with the reasons:
1. Remove the negative cable from one battery. It doesn't matter which one. This is the grounded side of this battery, so if this cable touches the truck body it doesn't matter. The reason for removing the negative cable first is because it is the grounded side. If your wrench should touch the truck while loosening the negative bolt, it won't matter. DO NOT allow the wrench to touch the negative post and the positive post on the battery at the same time or you risk melting a notch in the wrench.
2. Remove the negative cable from the other battery. The batteries are now isolated from the truck and from each other. If either of the loose cables touch the truck body it doesn't matter. Since the batteries are isolated from the truck, it doesn't matter if the positive cables touch the truck, whether they are attached to the battery or not.
3. Remove the positive cable from either battery. You may allow this cable to touch anything.
4. Remove the positive cable from the remaining battery. The batteries are now completely electrically detached from the truck.
5. Loosen the hold-down bolts and remove the hold-downs on both batteries.
6. Lift the batteries out. They are heavy. An Optima battery weighs about 45 pounds. The factory batteries are heavier.
Reconnect the batteries in the reverse order. That is, clamp down the batteries, connect both positive cables, connect both negative cables.
Good luck.
Loren