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1983 Mercedes SL 500 V8 R107 Red with cream/mushroom leather :P
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Discussion Starter #1
Hi there,

I trying to locate my OVP relay on my R107 uk spec (rhd) but am a little confused.

I've read and been told it's in up in the drivers foot well, but can't see anything with a red fuse on top.

See pics below.

There is a large silver 5 pin relay in the far right of one of the shots but that is fixed in and again has no fuse.

In the glove box, however, the is a relay with a fuse (and the fuse was blown!). However, it's a different part number to what I was told to look for. See pics.

Can any one confirm if this red ended relay is my OVP?

Also, can you confirm the part number I'm after?

Many thanks in advance.



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Yes, that’s your OVP. Original part number was 1265404745 and was replaced by part number 2015400845.



Your OVP might be good, just need replacing the fuse. Hope it helps.
 

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1983 Mercedes SL 500 V8 R107 Red with cream/mushroom leather :P
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Discussion Starter #3
Thank Elrick.

I've swapped the fuse already.

The car had, on occasion been cutting out at the lights (and once whilst driving) when the was warm, with the ABS light flickering on first (a sign I heard of a failing OVP relay).

Some pointed to the fuel pump relay, but since it's an intermittent issue it's hard to know.

Finding the broken fuse however seems to point now to the OVP.

Q: if the fuse has blown, is that a sign of a faulty OVP or of something else in the chain of components? Would a faulty FP relay trip the OVP fuse, for example?

Ultimately, I suppose I'm after what might have tripped the fuse in the OVP?




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Hi James,

There is a number of causes that might trip the fuse. The OVP itself might be faulty and you can check the condition by opening the case and checking the circuit board and its components are not corroded or burned out as well as the contact point breakers.

The alternator voltage regulator might be on its way out (replace it). Check your battery voltage output with engine running. Other components may also trigger the fuse trip such us ABS, SRS, ECM etc. But the OVP itself might be faulty after 29 years!!.

The symptoms you were describing are typical of the OVP fuse failure. After replacing the fuse see how the car performs.
 

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1975 450SL
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The OVP isn't really a relay at heart, it's an electronic device called a Zener diode. The characteristic of a Zener is that it won't conduct until a certain specific voltage is reached across it, then it "avalanches" ,or conducts fully. The way it's placed in the system for these cars is that the Zener is in a circuit with the fuse; when the specific voltage is reached, the diode conduct across the fuse, causing it to blow.

This prevents excessive voltage from going to critical components in the engine control unit (very expensive) and destroying things in there. It sends the Engine Control Unit into 'limp home' mode, but you still have a good ECU.

What can happen is that some electronic devices, like resistors, can change value over time and heat cycles, changing the curcuit parameters. Solder joints can also change with time and heat cycles.

If you changed out the OVP unit fuse, keep an eye on how the car acts. You could have only had a single spike during an attempted jump start, or a loose connection in the electrical system somewhere, or it could be an aged out OVP unit. Or it could be the symptom of an electrical problem. Just keep an eye on things, and hope you've fixed things by changing the fuse.

Good Luck,
Scott
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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Why are the connectors uncovered? If it was not properly mounted and just hanging with bare wires exposed anything could happen.
 

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1983 Mercedes SL 500 V8 R107 Red with cream/mushroom leather :P
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16 Posts
Discussion Starter #7 (Edited)
Yes, I saw those bare wires when I open the kick plate under the steering wheel. What would be best to cover them with?

I'm not exactly sure what the bare wired component is. As I found the OVP relay with red fuse behind the glove box?




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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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If read the number correctly, 107 820 00 10, that is the relay for the rear window heater.
 

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1983 Mercedes SL 500 V8 R107 Red with cream/mushroom leather :P
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Discussion Starter #9
Cheers guys.

Incidentally, Rowdie, is there a link/PDF to all/most R107 part numbers to save me pestering going forward? Or do you just have a really good memory :)


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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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EPC-net Online - Subscription Step 1 of 3 Free for U.S. residents. I do not know what a subscription costs for others. Only works on a PC platform.

There is also the on line service manual Model 107 which you can access. U.S. models only but most of chassis info is the same as the 380SL of the same model year. RHD and LHD also present a problem.
 

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w108 & w107
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Sorry to revive an 8 year old post (not even my wife brings up stuff from this long ago...), but i've looked everywhere for my ovp to try to resolve a high-ish idle (1000 rpm in neutral when warm) issue, but can't find it anywhere. I have a 1982 RHD 107.046 500SL. I've checked behind the glove box, and up in the footwell on the drivers side near the fuses, but in the passenger side footwell are the icu and ECU as shown attached. Not sure what that little connector is with the exposed green wires and connectors above the idle control unit...
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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0025454032 is the idle control unit. I don't know the other one. OVP should be above the fuse block. That's where it is on all LHD vehicles.
100_1722 1.jpg
 

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w108 & w107
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I had taken a photo of the area above the fuses to see what's there, and the silver relay is the rear window defroster, and the black relay is the intermittent wiper relay, below that are the window etc relays.
The other thing i noticed is that unplugging the idle control module does nothing noticeable to the idle or performance.
 

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560SL '88 Suzuki GS1000E '78
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Hi, for a RHD-car the passenger side footwell may be a good place to search. You should remove the side panel down there (that's just a guess).
Normally the OVP-Relais only suffers under cracks on the circuit-board. A little soldering mostly solve the problem.

 

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Hi, for a RHD-car the passenger side footwell may be a good place to search. You should remove the side panel down there (that's just a guess).
Normally the OVP-Relais only suffers under cracks on the circuit-board. A little soldering mostly solve the problem.

Thanks Martin, I'll have a look down there too. I'm just trying to eliminate obvious problems before i go further.
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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The EPC shows 001 545 92 32 installed in other 500 models but not the 500SL. Just says control Unit. Does yours have ABS?
 

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No - no abs on mine..., but i noticed the idle control module has 'w126' written on it in white marker. I have no history on what's been replaced by the PO, and by the way this is dangling behind the globe box, it wouldn't surprise me if it's been botched in there.
 
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