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Discussion Starter #1
Does anybody know what this relay is for? Can't find it anywhere in the forums! It sits on a metal piece over the main fuse/Relay panel. My problem is while trying to figure why the power windows don't work (works with 12V applied in door) I pulled the relay off and all the connectors fell off the back! Plus the relay felt hot even when it was connected, even with the key off.

What is that relay for and what order do the connectors go back on.

Also any one have a diagram showing what fuses go where? All the diagrams I've seen for the 72 450SL don't show power windows.

Thanks a bunch!!! These forums have been great in getting the 72 back in running shape!! Just need to chase a few more gremlins down.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Also any one have a diagram showing what fuses go where? All the diagrams I've seen for the 72 450SL don't show power windows.
It's been a while, but I have two pics of fuse panel on my HD. I think first one is for my car, second off a 73 450SL. The strips came out of my car, (I think)!

I have had that piggyback relay out, but at moment can't recall what it is for. My guess would be windows because they were added later just for NA market. But I could be wrong. Do your power windows work? All relays are same, so maybe wiring of others will give you a clue?
 

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Discussion Starter #3
Thanks!!
I've seen before where 3-4 are fuses for the windows. I read somewhere here that the relay in question that looks added on is the window relay. Now to figure what wires go where. Plus on the lower fuse strip the first 2 or 3 must have caught fire as the paper is burnt there and the second bottom from the front fuse has burnt plastic on the lower copper strip.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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Thanks!!
I've seen before where 3-4 are fuses for the windows. I read somewhere here that the relay in question that looks added on is the window relay. Now to figure what wires go where. Plus on the lower fuse strip the first 2 or 3 must have caught fire as the paper is burnt there and the second bottom from the front fuse has burnt plastic on the lower copper strip.
Looking at the 74 wiring diagram, Relay 70. 30 would be the heavy red wire and 87 the heavy black. The small brown would be the ground and connects to 85 and the other wire to 86.

Don't take my word for it - Wiring diagrams should be in the on-line manuals somewhere.
 

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One of the BW Old Guard/R129, W204 Moderator
1997 SL500- 40th Anniversary
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Looking at the 74 wiring diagram, Relay 70. 30 would be the heavy red wire and 87 the heavy black. The small brown would be the ground and connects to 85 and the other wire to 86.

Don't take my word for it - Wiring diagrams should be in the on-line manuals somewhere.
Agreed with above...
 

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Discussion Starter #6
Looking at the 74 wiring diagram, Relay 70. 30 would be the heavy red wire and 87 the heavy black. The small brown would be the ground and connects to 85 and the other wire to 86.

Don't take my word for it - Wiring diagrams should be in the on-line manuals somewhere.
That's the way I hooked it up but before I did I touched the smaller Black/red to the smaller brown and it blew the #11 fuse. The fuse panel diagrams above show either the rear window heater or window wipers. It appears to be neither as the wipers worked and when I turn on the rear window heater a bigger relay to the right of the eight relays clicks. I'll go thru the diagrams in the book but they don't look correct.

Is this mystery relay for the windows? The big red wire is always hot, the smaller red/black is hot with the key on.
 

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The big red wire is always hot, the smaller red/black is hot with the key on.
Ok that tells you it is an appliance that requires alot of juice when the key is on. What could take alot of juice?



Brown is ground. It kind of rhymes.
 

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One of the BW Old Guard/R129, W204 Moderator
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That's the way I hooked it up but before I did I touched the smaller Black/red to the smaller brown and it blew the #11 fuse. The fuse panel diagrams above show either the rear window heater or window wipers. It appears to be neither as the wipers worked and when I turn on the rear window heater a bigger relay to the right of the eight relays clicks. I'll go thru the diagrams in the book but they don't look correct.

Is this mystery relay for the windows? The big red wire is always hot, the smaller red/black is hot with the key on.
Sounds about right... This is a relay that energizes as soon as the key is turned on. The red/black wire energizes and connects to ground thru the magnet in the relay. The "always Hot" red wire is then connected to the bigger black wire, completing the intended circuit. It sounds like the FPR in the way it works, but double-check the wiring diagram for actual function. Similar function of the OVP, but the OVP is fused and designed to short to ground if voltage is too high (via a diode). If like the manuals I have, good luck in isolating it and determining it for certain.
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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That's the way I hooked it up but before I did I touched the smaller Black/red to the smaller brown and it blew the #11 fuse. The fuse panel diagrams above show either the rear window heater or window wipers. It appears to be neither as the wipers worked and when I turn on the rear window heater a bigger relay to the right of the eight relays clicks. I'll go thru the diagrams in the book but they don't look correct.

Is this mystery relay for the windows? The big red wire is always hot, the smaller red/black is hot with the key on.
The way it works on the 74, is that when you turn the ignition on, power is fed to relay 70 solenoid from fuse 12. The large red comes off the starter switch connection (30). When energized the solenoid switch closes and allows power to feed from (30) to both window fuses 3 & 4. Windows are then able to be used. This solenoid would only work once when ignition is turned on.

If you touch the smaller black/red wire to the brown (ground), you get a dead short and will blow the fuse that the black/red is connected to (fuse 12 on 74,75).

Added - It isn't the Fuel Pressure Relay - that is underneath it. You have to get the piggyback one off to access the FPR. In Chiltons there is a picture of the relays - Everything but that piggyback one which has to be for the windows.
 

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Discussion Starter #10 (Edited)
Thanks!! Verrrry interrrrestinc!

That relay and the resulting answer's here with maybe a pic should end up in the sacred stickey for 450SL's.......

Which of the above fuse panel papers go with my 1972 450SL setup?

The big black wire is actually brown under the sheath but I think with everyones help it's starting to make sense. I have yet to see an actuall diagram/picture with the piggyback so maybe that was a one year (1972) thing?

One thing I noticed is when the relay energized (now that I know what wire goes where) the red wire on 30 would read 12V (of course) but when I put a meter on #87 I got a very slow ramp up to 6-7V. So tommorow I'll swap out another relay and check again.

So if I understand, fuse #3 and #4 are then powered so I should see voltage at the window switches that then go to the windows.

Almost forgot....What are the 2 fuses on the piggyback panel for? Might as well get the whole piggyback thing/question answered.

Turns out the burned up fuse section was from some random wire that was MickeyMoused to it and dead ended. They must have cut it from whatever accessory they had rigged up when the smoke started!
 

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R/C107 Moderator
1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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What I don't recognize is the two fuses mounted on the same panel as the relay.
what is the chassis number on yours? Mine is 2913 and I don't recall those.
 

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A really cool tool to use is a Power Probe? It can help you identify what is getting power, and you can also send power to specific wires. Also, you might want to try hooking up a self-powered test light to the wires and start probing around. If you suspect the windows, start probing the window's wires, and then probe the wires on the relay. It's tedious work, but it works.
 

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Discussion Starter #14
What I don't recognize is the two fuses mounted on the same panel as the relay.
what is the chassis number on yours? Mine is 2913 and I don't recall those.
I'll check tommorow. Is the chassis number on the engine compartment tag? My plate in the door was removed in the past during a paint job and never reinstalled. Is ther any way to get a new replacement plate from Mercedes? It's the car the title vin refers to as the same vin is on the radiator support bracket plus I have a lot of the original docs from the original owner including those wierd punched thru tickets with option codes on it.
 

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1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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It should also have a tag on the windshield A pillar visible through the windshield.

Example: 107.044.12.002913
 

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'72 350SL, '85 300D, '98 E320, '19 Subaru Outback (sold '14 GLK250)
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I don't know which of the fuse layout diagrams is correct for the NA 350SL with power windows etc. Apparently even in same model year these can change. The second one (1973 450SL) looks close. I went through same exercise and thought I had figured out which one to use, printed it and had put it in car. But just looked in car and I have no diagram :confused:(should be stuck to inside of fusebox cover). The fuse size strips in pic I posted were from my car so at least I know what size fuse to use even if I don't know what it does.

I have attached a couple of pics of my relays - Maybe we do have fuses inside that black box? If so, what are they for?

Rowdie - do you have that black box?
 

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R/C107 Moderator
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The fuses are there in your picture. There is a cover over them. He is missing the cover. Could be why I don't remember seeing them
 

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The fuses are there in your picture. There is a cover over them. He is missing the cover. Could be why I don't remember seeing them
Yes - I corrected my previous post - But what do those fuses protect? Perhaps something Euro cars did not have ?
 

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1986 560SL: '84 500SL: '84 280SL 5 speed: other 107s
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I will check later when it warms up a bit. I have no idea what they are for.
 

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I will check later when it warms up a bit. I have no idea what they are for.
I posted question over on Peachparts - Melted there has a '72 and hopefully has diagram.

Checked EPC and couldn't find that fuse holder for early 107s. Did find the mounting bracket though.

Maybe those are not fuses? But they must be - look like 16A reds.

PS: Also noted my EPC runs out in 30 days. Wonder if they will just let me renew? Had help from USA in getting access!
 
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