318i short circuit

Just got an electrical problem and wondered if anybody had hints about where to look.
It's a 1984 318i. The radio (a recent one from the previous owner),
clock, glove compartment light (there is one, right?) and dome light on the driver's door are out. So I checked the fuse and it was blown. Tried a new one and it blew immediately as it went in. So I'm not sure about where to start on this.
Some other info that should be unrelated. I had taken off the fuse cover a few days earlier and the catch on the cover snapped, so I had driven briefly without the cover, but it all looks clean and dry. Next, the trunk had been left up overnight just before this situation happened. Speedometer has been intermittent for some time.
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wrote:

Library?
If you don't have a manual, start at the library and trace the circuit for those devices.

I'd start with the radio as it's been owner added and probably the most recent change in the electrical system. Look for a "black tape fallen off and skinned wires touching the frame" problem. Thou shalt not replace the fuse with a higher value.

The snap is off my fusebox cover too. It sits on there fine without it.

Probably unrelated. Bad luck runs in multiples though, right? My trunk ('88 325) has a light in it, which I guess could heat the circuit if it was on all night.

Does it come on if you flick the dial with your finger? (my temp gauge is like that). If so check the connectors on the back of the dash. Also, some models have a battery in the back of the dashboard that needs replacement every four years or so. I don't know if the speedo is part of that setup though. Good luck and happy motoring.
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