Here it is in a nut shell-For full disclosure, I have limited auto mechanical skills.
71 challenger 318 built into 340 clone fully restored in 2012 and when I picked the car up it was 100%, every light, buzzer, gauge worked as it should. Standard dash was converted to rally. Mopar electronic ignition conversion. Mopar original repop yellow cap battery. Car ran flawlessly for 4 seasons with the exception of some thermoquad tuning issues. In 2014, I installed a repop "rim blow" steering wheel. The repop wheel has a non functioning horn switch but it did have a tab for the horn wire to attach to so I hooked it up to it so it would not be floating around in the steering column. The car was driven for weekend shows and cruise nights with no issues. Right before the end of show season, Oct 16, I had the car outside my garage running and out of the blue the horn began to beep. I thought that was weird and I disconnected the horns by removing the wires at the horns. At that point, I didn't even remember that my rim blow had a non functioning horn switch and I drove it a couple more times with the horn DC'ed and put her away for the winter. Fast forward to Feb 17 and I send the car to my regular mechanic (friend since high school, totally trust him, 50 years old, several muscle cars in the 80s) to get new leaf springs installed and while he has it see if they could swap a different thermo quad on there and try to tune it right. I get the car back and when I drive it home from the shop, I notice the oil pressure gauge is not working. I get home, check under the hood and find the oil gauge wire disconnected from the sending unit. I figured it got knocked off when they swapped the carb and I reattached it and put the car back away for the remainder of the winter. April 17, The weather breaks and I take the car out for it's first run. I now notice that my oil gauge has activity but all 4 gauges in that pod are now acting funny. Gas gauge bouncing way more then normal, sometimes looking like no power and just falling limp, Temp gauge working intermittently, charge gauge all over the place and oil pressure also working intermittently. Mind you sometimes all or some go back to normal operation. Talk to mechanic, says nothing to do with changing springs or carb. I drive the car for about and hour and put it back in the garage with trickle charger on as usual. 5 days later I try to start the car and it won't turn over, clicks like dead battery. Volt meter shows 13V at battery. I use jump pack to get it started, back it out of the garage and figure I will let it run to charge up the battery. The car runs for about 3 minutes (gauges working at this point), I hear a pop, immediately smell electrical burning and see light smoke outside the windshield coming from the voltage regulator. I shut it down and remove voltage regulator, the back of it has a melted spot and smells burnt. Talk to mechanic, it's Sunday and he is out of town but instructs me to replace new voltage regulator and then check charge gauge operation. I replace voltage regulator but before I jump it again I tried to hook up the horns to see if the battery has enough juice to beep them. Headlights working the whole time. When I connect the wires, It sounds like the horn it trying to beep but really not working. I remove the center cap or the steering wheel, DC the horn wire from the fake switch, now I try to operate the horn by grounding the wire to the steering column and as soon as the wire touches metal, the key in ignition/door open buzzer begins to operate, no horn. Weird. So I now use jump pack again to start car. Car starts right up, but now the only gauge that is working is the charge gauge and not only are the other three gauges in that pod not working but everything inside my car is not not working, no tach, no clock, no dome light, no key in ignition buzzer, no lights at shifter in console. Can't get back in touch with mechanic so I let it run to try again to charge the battery. It runs for about 10-15 minutes and I want to test the blinkers, as soon as I put the blinker on the car stalls. At this point I want to give up and just get the car back in my garage until my mechanic can get to it. I jump it again, try to put it in gear and it stalls so that is a no go. Get back in touch with my mechanic. He instructs me to look for burnt wiring/fusible link. I start at battery, inspecting wires, work my way to ballast resistor and when attempting to remove the top wire it crumbles in my hand. I replace that, car starts only with a jump, I pull it back in the garage and now it is time to get her fixed so I can get a few hours on her before I trailer her to Carlisle. I know this is a lot to digest but if any of you have some guesses of what may be going on so I can give my mechanic any ideas I would be forever grateful.

Is there a fusible link that protects the interior gauges and lights? Possibly the pop I heard?