'98 986 Heater ac control panel has no power
 

Everything worked [but the horn] after purchase and a 100 miles. The car sat for 6 or 8 days and the battery went dead. I charged the batt and drove some but noticed, then, that no switch on the control panel worked. Fuses D-6, E-7 okay and relay 18 too. I changed out relay 18 and relay 9 and still no response from any switch button pressing.

Did you disconnect the battery before charging it?

Battery was not disconnected from the car. Battery charged only long enough for me to start the car

Line surge or charger error probably killed it.

You should always disconnect the battery before charging. I also will not use a maintainer that is hooked up with the battery connected, but that's just me.
99.9% of the time, there will be no problem. However, it is possible to fry sensitive electronics in your car anytime you connect something to it that is powered by AC.

You'll likely have to replace it.

Sadly, that appears to be the case. I have two 911's; the youngest is 42 years old. With those, there hasn't been a problem I couldn't solve/fix. This 986 is new to me; lesson learned. (Made a shop appointment already). Thank you!