Wow, what a blast from the past. My first car was a 1990 Mercury Grand Marquis, and it developed this same solenoid issue. My grandpa taught me that same trick of shorting past the solenoid so that the car can start. My friends were always very curious why there was a hammer underneath the passenger's seat, at least until I told them to hand it to me and crank the engine when I gave the shout.
Kind of wild that both you and GP developed tricks for shorting the solenoid when a replacement solenoid is like $20 and 10 minutes of work. Well, at least for a Mercury Grand Marquis aka the Ford Crown Victoria, I can't speak for Superior German Engineering.
The neat thing about Ford solenoids of that era were that they were very conveniently located near the top of the firewall and can be easily triggered manually if needed with a big screwdriver across the leads. (And hope you don’t get electrocuted in the process.)
Contemporary GM solenoids were integrated into the starter motor and were a real pain to get to. Certainly not impossible to do the screwdriver trick but far less convenient with needing to crawl around on the ground and all. Being located right next to the exhaust headers also meant they were easily susceptible to heat soak problems which would cause a failure to activate - especially if you have a hot-running high performance engine. It was actually a pretty common and easy mod on those GMs to use a Ford solenoid and bypass the one on the starter motor.
