5 pages on this. These voltage drop discussions are out of control. Look keep it simple. THERE IS ONE WIRE feeding underhood loads. ONE. IT is the dark blue IGN1 "run" wire. if you unhook one load of course it changes, because you have changed the LOAD
Follow the path. I like to call it the "functional path" and was criticized for this, as sometimes I go from battery + even though I was taught "electron flow theory." But the path is a circle from battery + clear around through all the splices, connectors, switches, and components to the ground/ frame/ body/ block and back to battery NEG (Or the other direction if "you must" flow electrons LOL)
So follow the path and check the CONNECTIONS. The ignition switch, the switch connector, the bulhead connector, the ammeter and it's connections, (even the welded splice) and so on. FOLLOW THE PATH
"What is?" the path? On a stocker, and for "run" underhood loads, the path is "pretty much"-------
Battery-------wiring to starter relay stud-------fuse link-------through the bulkhead (ammeter RED)------to and through the ammeter---------out on BLACK to the WELDED SPLICE--------to the ignition switch connector----------through the switch--------back out the connector on dark blue "run"----------through the bulkhead connector----------through the engine harness "WHITE" connector on newer models-------and to various underhood loads, which are simple splices in the harness
