Way back in the old days, you could buy a spring mount for your Cadillac that was wired into the horn circuit. Grab the hood ornament and the horns would sound.

Since I'm a cheap bastid, I took a microswitch and wired mine into the alarm on my old Caddy. I've not looked into mounting options on the Benz, but I'm sure I could figure something similar out.

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1989 300 SEL that mostly works, but needs TLC