Tonerman, here is the kicker here. 1969 is little past our usual gig here. We do not have a wiring diagram for it. The 69 dash has either idiot light or an actual "battery" gauge. You seem to be adding an aftermarket ammeter. You chose not to replace whatever is in the cluster. The 1969 had moved to a more moduled approach with a printed circuit board on back of the gauges. Which has a connector and all the wiring harnesses to connect everything properly. Including the ammeter or idiot light.
You now know the general idea of an ammeter.
We don't know how you are going to connect the various wires from a printed circuit board and it's connector to you ammeter. That's up to you. In general most wires except for the 12ga from battery to ammeter, are per a wiring diagram. 20ga to 14ga. We don't know how you will connect other harness wires to the aftermarket ammeter. You know that almost everything should be feed from the ammeter. Probably should have done a volt meter. MUCH MORE SIMPLE IN YOUR CASE.
The ignition switch usually turns on some fuses in the fuse box and some fuses are "always hot". So many accessories will get power from the fuse panel. Ammeter to ignition, ign to fuse panel, if that is what the diagram says. Some things have a separate fuse/separate wire, maybe wiper, heater, light switch whatever. Just get them wired. Some things get direct power from the battery, your truck may feed battery power to the horn relay and use it as a "terminal block" to feed power to some things. light switch, ignition, etc.
You will need to refer to a 1969 C10 diagram or someone may post one here.
You know the plan, the hook up. Do it the best you can. Don't worry about how many connections or length. Everything is short under the dash anyway.
Is your alternator internally regulated or do you have a separate voltage regulator box?
Just to throw this in for the archives. When you see a negative symbol on the back of an ammeter (-)...It DOES NOT mean ground.
