'68 Barracuda - charging system questions

"With a jumper wire between the alternator and the battery positive, charging power should go right to the battery." That sounds good to me. OK so I get 12.5 or so on blue IGN wire of voltage regulator with car running. With engine running, I tested some of the fuse block hots and found the one for instrument lights had a voltage drop to 11V when I turned the lights on with headlight switch. This fuse has 2 wires tapped into it that supply power to 1) the LED lamps in the after market small gauge cluster..and 2) something else I still need to find...we'll see . Because power source for instr. lights circuit comes form headlight switch, I am thinking corrosion/weak connections/other issues in that switch could be reason for drop - does that sound like a possibility?