Welcome and thanks for the pick's
We have seen rougher.
Check/replace the the ign switch as Roland suggests.
The plug on the back of the switch is known for problems as is the switch itself, especially when they are exposed to the weather as your pix's would indicate.
What you will find is the male spades on the switch corrode, reducing the conductivity, producing heat and most times melting the plug, mostly the one from the battery.
sometimes wiggling the plug produces a temporary "fix" only to occur again at usually an inopportune time.
Also one finds the spades on the switch are loose on the attaching rivets.
Other times they are plum rotted off, or so corroded they break off easily.
Bottom line, replace the switch with the correct one AND the female terminal ends/plug.--- delphi-packard GM 56 series
Example: ebay listing # 382231331196
There are also some that sell the plug on a pigtail with terminals attached to wires.
Have fun!