Had an issue with my pretty much stock '83 bready since i got it about 5 years ago. If i leave it a couple of days without disconnecting the battery, something drains it. I got a lead, (no pun intended,) a couple days ago by chance and was looking for a second opinion. 

Apparently it could be down to aftermarket stereo. The stereo that was in it when i got her was aftermarket but i have since upgraded. No extra amp just new head unit with dab, usb and aux. Could this be the culprit? If so, what's a good way to trace it as I've never used a multi meter, and is there a way to fix it that someone with not much electrical xp points could carry out?

Thank you for stopping by and for any guidance you can give. 

Take it easy. 

Most head units the power they require for memory should not cause a battery problem, as it's milliamps, if the battery is failing then any drain will be exposed,  if you connect your multimeter on the 20Amp range to start with and put it between the battery pos terminal and the removed cable and see what the current is, then start re moving  fuses until the current flow is at its lowest, then you can workout the highest current drain

Thanks. I'll grab a multi meter and start checkin fuses. 

I can use the stereo without a key in the ignition. Is that supposed to happen?

yeah as standard theyre wired to be on all the time

 

id disconnect it and see how it goes

That's good to know. Thank you Sir.