Dealing with voltage can be tricky, especially with older equipment like your klaxon horn. It's cool that it has sentimental value from your grandfather!
So, here's a little story that might help. I once found this vintage radio at a flea market. When I plugged it into a modern outlet, it crackled like crazy. Turns out, it was designed for a lower voltage system. I ended up using a voltage regulator to get it just right, and now it plays my favorite tunes perfectly.
For your horn, have you considered using a voltage regulator or maybe even a resistor to fine-tune the power? It could help balance out the speed and volume, making it just right for your Jeep. Oh, and I stumbled upon this cool train horn online (https://bosshorn.com/products/milwaukee-train-horn) that might give you some insights too.