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  #1  
Old 07-20-2020, 03:29 PM
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Fuse Box Question, Burnt pins= Electrical Gremlins?

Hope someone is more familiar with old Merc fuse boxes,

Recently pulled my fuse box to clean out the area around and behind it, and also to check on the health of the fuse box. For reference I am working on a 1991 190e 2.3. Once removed, I noticed on the undersized some corrosion, and then several pins that appear to black/dark brown. Prior to pulling the fuse box, over the last year and a half, I have experienced erratic electrical gremlins and yet none of the fuses were blown. My Issues included: Non functioning cruise control (broke sometime prior to July 2018 when I bought the car), fluctuating interior lights, erratic radio (12v constant would dip way low and then super high, causing antenna to go up and down), and recently pieced together that at some point the Aux fan magnet must have failed because a brown wire leading to the coolant temp sensor is clipped and exposed, and the fan just slowly spins at all times. Any possibility that this is in correlation with the Fuse Box? Also the plastic housing of the fuse box has what appears white oxidation all over it. Any help would appreciated.

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Fuse Box Question, Burnt pins= Electrical Gremlins?-fuse-box-w201.jpeg   Fuse Box Question, Burnt pins= Electrical Gremlins?-img_3537.jpg  
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Old 07-20-2020, 04:56 PM
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There don't appear to be any burnt pins in your photo. MB's of this era used silver-plated contacts and pins that will darken with age. Your erratic voltage in the car is most likely the regulator failing on the alternator. Replace it before it leaves you stranded.
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Old 07-20-2020, 05:55 PM
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Thanks for the input! The issue is the pictures dont seem to refelct how dark some of the pins are, specifically on plugs S and U (also forgot to upload the other portion of the box). Hopefully this weekend I will be able to pull the fuse box from my parts car (92 2.6), and take some side by side pictures for comparsion. As for the alternator it is a 90amp bosch unit (unlike alot of things on my little m102, defintiley not original).
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Old 07-20-2020, 09:22 PM
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The silver plating can turn jet black. Color means nothing. Overheated pins will have melted wire insulation on the back side, a blistered appearance, and usually melted plastic around them. You have none of these.

Alternator size doesn't matter. If the brushes are worn out on the regulator, you'll get erratic voltage from it. The dipping lights and various flaring you describe is a classic failing regulator. Fix it before you're walking.
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Old 07-21-2020, 12:53 PM
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All valid points, I have been planning on replacing the alternator with a larger unit anyways, but once I have the fuse box back in and the battery hooked up, I can start trouble shooting these issues. Aside from the resistor for the aux fan being cracked (located by the drivers side headlight), I do not see any components that look damaged. I will also note I replaced the OVP three months ago, when I pulled the one in the car the fuse wasn't blown but it fell apart upon removal (can't remeber the brand, but it was clearly super cheap and flimsy).
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Old 07-21-2020, 01:32 PM
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The voltage regulator is a $20 part and is easily replaceable. You're farting in the wind if you skip that step. Unless you're running some insane stereo or enormous electric fan, 90A is more than adequate for a W201.
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Old 07-21-2020, 03:46 PM
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Yes I aware that the regulator would need to be replaced wether it is worn and I keep the 90 amp alternator or if I go for something larger. Also forgot to mention the battery I have is much bigger than stock its rated at CCA 850 and CA 1000, replaced in December 2018 and the same specs as the prior battery the previous owner had in the car. It is healthy and been on/off a maintainer since I pulled the fuse box.
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  #8  
Old 07-21-2020, 03:48 PM
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Who cares about the battery? The diesels have used the 900-1000CCA batteries since the 70s and have as small as 50A alternators. You're focusing on all the wrong issues. You seem to know what you want whether its warranted or not, so let us know how it turns out.

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