a puff of smoke and now nothing 69 valiant electrical issue

Maybe I can help Disconnect both battery terminals!!! Double check your ammeter connections on the back of the dash. One wire is a 12 Gauge red wire, this comes from the battery to the ammeter. The other is a 12guage black wire and runs to the ignition switch. If theses are correct. You need to check the Fusible link, it is basically a smaller gauge wire that will burn first, the weak link in the chain. This to protect the wire harness. Unfortunately sometimes they locate this in the cluster of wires at the bulkhead connector which is not very accessible. The connection here at the harness which carries all the high current and is notorious for starting fires at the bulkhead due to corrosion/resistance which cause it to heat up. Then you need to check the fusible link. You can use a cheap voltage probe with power on but in your case I would be hesitant as you may have a created a short grounded. the safe way to check the fusible link with power disconnected is to use any cheap DVM set to low resistance or continuity mode. Connect the DVM meters black wire to the ammeter 12 gauge red wire, then use the other to probe the 12 red gauge wire that comes from that red wire at the starter relay. You may need a long extension wire to reach it. What your looking for is continuity between the ammeter red wire and that same 12 gauge red wire that goes to the starter relay(which the battery is connected to) This will tell you if the fusible link is blown and or the resistance of that infamous dangerous high current connection between the firewall and passenger compartment. I am working on my car now going through all the wiring. I am going to bypass that firewall connection by running a new red 10 gauge wire through a another firewall grommet. I have heard one to many stories of that high resistance connection starting a fire right at the fire wall. I am moving the fusible link to the starter/battery side instead of at the firewall. When these fires start they will take out your entire bulkhead harness. I hope this helps. A note is if I remember, fusible links are 2 gauges smaller that the wire it protects and has an improved insulation and keep it short like 4 inch's. I recommend using non-insulated connectors, then soldering and use at least 2 layers of good shrink tubing. hopes this helps