Replaced fused, now car won't start

Hi all

Newbie here. This week the gauges and choke indicator light on my 73 240z went out. I checked the fuse box and noticed that a 20 amp was shot. I replaced it with another 20 amp fuse, and immediately after that I was unable to start the car. I can jump start it, but without jumper cables the car can't start on its own even after I've let it idle for a while. After reading the posts around here I now know that using the alternator to charge the battery is a no-no, so I'm off to buy a battery charger. If that doesn't work then I guess it's a new alternator and regulator for me.

Can anyone tell me why replacing a fuse would cause this though. I'd still like to replace the fuses in the hopes of getting my gauges to work again.

This site is a great find!