I'm have some electrical issues with the 380SEC I'm working on.

1st the battery is draining after a couple of days of sitting. It's a new battery.

2nd The radio was working, but wont turn on now. The fuse is good.

Could these issues be related?

Sure. Simple test:

Remove the + cable from the battery. Get a small test lamp (a couple watts) and hook it between the cable and battery. If the light glows brightly you know something is drawing at least as much power as the light is rated for. Disconnect fuses on at a time until the light goes out. You don't have to totally remove fuses, you can just lift up on the tabs to disconnect them for a moment.

When the light goes out you have found the circuit which is drawing the current. You can continue your troubleshooting from there.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.