OK, I have a 1982 300 SD, and I Stupidly left it parked OUTSIDE for 4 years in Humid Gaston County NC... I know sorry. (man will that mildew smell EVER go away?)
well now I am determined to make this my daily driver so I gotta fix all the electrical problems.
the hazzard/electronic radio fuse when connected will drain the battery. and the radio shows odd display. I plan to remove all the electronics from the dash and replace. I have a donor car, but MAN this looks daunting. (everything worked fine when I parked the car... STUPID STUPID STUPID!!!)
A/C will not energize, tach no go, although it does swing all the way to 6000 when the turn signals are on???
and the turn signals don't blink, well they do, but it is so fast it sounds like a buzzer and they look solid.
also, the cruise control worked when I started driving it again,but now it is also gone south... cleaning may help, but I bet it has condensation corrosion too.
condensation for 4 years will really wreak havok with theese cars.
anybody got any suggestions on where to start?
John

A friend of mine buys a lot of cars that have been sitting for years. The first thing he does to the electricals is to remove all plug in or terminal fastenings. spray clean them, lubricate and put back together. That is probably time consuming but his choice. Includes all grounds needless to say and any moving or stationary contact points. You could just trouble shoot each issue on its own. No other ways that I am aware of unfortunatly. His way restores general reliability but at a painful cost to some extent.

OK, I'm assuming you have installed a new battery (should be step one). I'm also assuming you removed all fuses, cleaned the fuse ends and the fuse terminals. (do that with batt disconnected). Also it would be a good idea to remove and clean the major chassis grounds. (batt, chassis, engine, etc....)
Seems like when folks have really weird electrical problems, the alternator can cause odd things to happen. The brush assy can be replaced.
This is at least a starting point, and the more knowledgeable folks can chime in.

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Jimmy L.
'05 Acura TL 6MT
2001 ML430 My Spare

Gone:
'95 E300 188K "Batmobile" Texas Unfriendly Black
'85 300TD 235K "The Wagon" Texas Friendly White
'80 240D 154K "China" Scar engine installed
'81 300TD 240K "Smash"
'80 240D 230K "The Squash"
'81 240D 293K"Scar" Rear ended harder than Elton John

Techie freind of mine told me years ago that when you come upon a goofy electical problem, always check the ground first. He said it goes that way even twice as often with 12 v dc.
Rememeber that when you are feeling the frustrations here. This will take some patience on your part.

Before you go to nuts give this a try:

Order a bunch of the new copper fuses(Phil sells thin in blister packs, dirt cheap), replace every fuse in the fuse box and sand the terminals a bit. Now see if some things come back on line.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200