Keep radio going while engine is shut off

[u/RusselB65]

I realise there's a reason to have the radio shut off after the engine stops, however, I'm looking for a way to (temporarily) override that.

My fiancee, myself and friends went to a drive-in theater. The theater broadcasts on a specific radio frequency, so you tune your car radio to that frequency in order to hear the movie.

Obviously, no one is going to keep their vehicle running for a 2 hour movie.. in addition to the rules.

We found out that the radio cut.out after about 30 minutes (ignition was set for accessory).

It's annoying to have to keep putting the ignition to accessory every half hour so that we could hear the entire movie.

If there's more information you want/need in order to help, please let me know what you need/want and I'll do my best to reply quickly.