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Old 08-31-2013, 10:57 AM
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Join Date: Aug 2013
Location: Portland, OR
Posts: 12
86 300SDL compression test & electrical issues

We just upgraded from an 85 300D with 220,000 to an 86 300DSL with 230,000 in anticipation of the arrival of baby #2 in November. Purchased from a Used Car Dealer, never a good idea, but was able to track down previous owner via insurance card left in glove box prior to purchase. Interior and exterior are in excellent condition, with beautiful and firm blue leather seats and clear coat intact.

The only obvious issues are the need for new tires, new rear brake shoes, a new air filter and finding a short that is blowing fuse #15. But before I describe the electrical issues, I'm looking for feedback on the compression test I had done at the local independent Mercedes garage. Here are the numbers:

1) 308 2) 318 3) 268 4) 322 5) 324 6) 343

So, what should I take away from this test? The shop that did the test told me the low number of cylinder 3 suggest the card will be hard to start in the winter, but living in Portland, OR the temp rarely drops below 40.

What, barring a complete overhaul, could improve compression?

Now on to the fun stuff, tracking down a short. Upon opening the fuse compartment, I discovered that fuse #2 was blown and fuse #15 missing. I replaced #2 and now the key/door/lights on buzz is somehow connected to the brake pedal. The buzz is on with all doors closed and key in the ignition, and stops when I depress the brake pedal.

Upon replacement, #15 blows immediately, and in arcs on installation. Here's what the 2 fuses protect:

#2 - diagnostic terminal 6, hazzard lights, clock, front dome light, radio, vanity mirror lights, electric illumination control

#15 - rear dome light, trunk light, safety belt handover arm, switch over valve seat back arrester, central locking system, door lights, rear reading lights, antenna, control unit seat adjustment memory

There is no after-market equipment installed. factory radio and factory radar detector. I did notice a inline fuse on a wire to the negative battery terminal.
Also, without fuse #2 installed, radio will operate with the driver door open, but is killed by lower door switch.

What are the 2 separate door switches / depressors on the doorframe designed to control? An alarm? Is any of his behavior familiar to anyone?

Sorry about the long post. All and any feedback is appreciated.


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