I've was given a 1984 300sd recently with the best motor 617 I have seen. No blow by quick start and great mpg. But the electrical system is messed up. The radio will turn on and off her and there. The Interior lights work on and off and the windows also. The dash lights act weird and so do the gauges. Any idea guys?

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84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800

First, check grounds and clean and/or tighten as needed.

Window switches are known to get internally dirty and act up.

Further, get a wiring diagram and go through and check everything.

Hope this helps...

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Current fleet:

1985 Mercedes-Benz 280TE - Waiting for heart surgery.

1985 Mercedes-Benz 300TDT - Rear ended 23 September 2016 and now looking for a new home.

1979 Mercedes-Benz 300TD - Parted out.

1964 Volkswgen Beetle - Vater's since September 1968 and undergoing a restoration.

1971 Volkswagen Sunroof Squareback with F.I. - in need of full restoration.

1971 Volkswagen Squareback automatic with F.I. - Vacationing with her caretaker until he is in better health.

Sounds like:

#1. A loose ground.
#2. A damaged alternator.
#3. A ground butchered for after market radio.
#4. The massive BROWN ground wire group behind instrument cluster suffering serious corrosion.

.

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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

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After dealing with the grounds. Incidentally cleaning and reseating them should be perhaps considered just normal maintenenace after so many years.

Use a dielectric to avoid any possibility of future corrosion issues with them. Even if the problem is solved I would also check the fuses for any corrosion or replace them with a better type. Plus clean their contacts as well. Also adding a dielectic paste on the contacts to block oxygen access.

This once accomplished may or may not restore everything to a working normal condition. Plus it's cheap to do. Then if you have to further troubleshoot you have a sounder basis to do it on.

With all my years of electronic service behind me electrical troubleshooting might be easier for me than many. I still want a solid basis to do it on though with an old vehicle.

I do all the grounds reconditioning usually as a maintenance thing even if there are no current issues. No pun intended. Chasing down intermittent conditions like you describe otherwise in car electrics can be more frustrating otherwise. Grounds that are not conducting well because of corrosion also lower the available current to devices. Actually may over time damage something else on the same marginal ground leg as the device you are asking to work uses another device as it's partial ground if the common one is somewhat or totally compromised.

Your windows go up slower than when new for example. Your starter solenoid circuit a less than a stellar design on several european car brands. So electrically develops a little further resistance. I have seen overall improvement to electrical systems by just cleaning them up sometimes. The plating on electrical terminations is somewhat self sacrificing over time. It was never a design intent by car manufacturers for it to last 30-40 years. The lifespan of contact points is somewhat determined by the environmental conditions plus dissimilar metals proximity.

After cleaning them there may not be much of the plated protection left on them. This is one major reason to use some form of paste to block access of oxygen to them later. No oxygen no more developing corrosion at those junctions. I never remember having to go back to a well treated older connection again over all the years I have kept the cars if I do this to them.

I will go through and check the grounds. Any idea where I can find a wife diagram.

__________________
84 300sd 2.47 dif 360k
26 mpg needs lots of love
given to me in pitty

89 civic hatchback auto 140k
33mpgs soon to be low to mid 40's
been in the family since mile 1

85 300d with unknown knock. driven over 30k with knock and still going. sold for $800

Let us all know when you find your "wife diagram". I am sure the rest of us would appreciate knowing how they are wired!

John

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Certified Registered Nurse Anesthetist (CRNA)
2002 F250 powerstroke with Plantdrive WVO conversion
1983 300SD 190K miles ,sold
2006 E320 CDI