560SL electrical blues

[marci hixson]

My 1988 560SL (156K) had a new alternator installed 3 months ago after going haywire (dials erratic, systems shutting down one by one). All went well for 3 months, then the car went dead/wouldn't jump. Diagnosis: bad alternator ("this happens"). Four days after the new alternator was installed, I found the dome lights on, not responding to the switch, so I took the bulbs out. The next day, the dome lights, clock, radio, glove box light, and trunk light didn't work. Back to the shop. No diagnosis, but one dome light was replaced and everything seemed to work. Next day, the dome lights were on, but did turn off with their switch; however, the clock had lost 15 minutes. This problem is not fixed; it's just a matter of time before something else pops up.

Any ideas? Up until now this car has been great, just routine and age-related repairs.

[tecqboy]

Diagnosing electrical problems requires a step by step logistical approach. There really isn't enough information in your post to guide me to help you to find a specifically failed part. However, in a car of that age, it would not be unusual to have badly corroded battery and alternator cables. Over time, the heavy copper wire can break down, even under the insulation where you can't see the problem. Also, the ground connections can corrode, especially the connection where the negative battery cable is bolted to the chassis and engine. I'd like to think that the shop that replaced your alternator is sharp enough to find your problem.

[cbdo]

It may not be your problem, but there've been lots of posts along the way bout the fuses our cars use; they develop some corrosion over the years and become weak without visible degradation. Replace all of them and see what happens.

[Strife]

I'd replace the aluminum fuses with copper (available anywhere, on eBay for example); also, I'd consider that the battery may be shot after being abused by a bad alternator. If it's been chronically undercharged ,or overcharged only for a short time, it will never be the same. Only a true current load test can adequately test a bad battery.

PS: There may be more than one problem going on here. The clock ought to be able to run on just about any voltage (I tested one with a 9V battery, it worked fine). The clock may be on the way out, but it's repairable. Search the site.