So, I have an 1983 245, when purchased the fuse box had excessive corrosion and that was taken care of.

Now, i'm still having quirky problems like windshield wipers not working, or very seldom, the car won't start until I fiddle with the fuses. I can deal with this part.
But the more serious problem I'm having is something seems to be draining the battery every 3-4 days. The alternator has just been replaced, and at first thought that was going to solve the problem, but after a 3 hour drive to get it home, the car died when i slowed down and it went under a certain rpm (all three hours running the radio and the lights were on).

Busted out the multimeter, and checked the fuse box, nothing seems to be pulling more than it should there. At first i thought it had something to do with the lights, because the 3 times it happened, I had been driving at night and using the lights (once after a 3 hour drive, but once after driving maybe 10 minutes, and the 2nd time had driven maybe 45 minutes), and if the car was at too low of an RPM it would just shut off and act like the battery was dead.
After the last time it died after I had been using the lights (driven 10 minutes, was doing a slow turn around in culdesac), i discovered that the positive battery cable was bunk, and ended up replacing that, car started up like nothing had ever been wrong (except i made one bad error and killed the battery).
So, I swapped batteries with someone, and was driving not using the radio, heater, or lights (just driving during the day). Everything was going fine, went out one morning, and it wouldn't' start.

I can't find any exposed/loose cabling, and I've even replaced all the fuses in the fuse box with new, ceramic ones after again cleaning all the connections.
I've done all the normal battery troubleshooting i can think of and have read to do on this site....
I'm at a loss of what to do next? Any suggestions, ideas, or help would be amazing!

Thanks!

 

I would try disconnecting the negative terminal of the battery when the car is not being used to see if it still goes dead after a few days.

If so, it's probably a sulfated battery that is draining down when not being used.

If not, I've disconnected the negative terminal of the battery and put a voltmeter or ammeter between the negative post and its cable to see if there is a load when the engine is not running. If there is a load, take out the fuses until you see which one has the load on it and look for which item on that fuse that might be causing the drain.

 

Yes, what Mr. Malloy said. You've probably got a short somewhere that's causing a drain when the car is turned off. It will drive you nuts finding it, but ultimately should be cheap to fix.