My son just got an '86 300e and the blower motor is not functioning. It does not appear to have the fuse upgrade (or at least we cannot find it if it does) and the blower motor is not getting the 12 volt signal. After removing and checking the motor we did some more diagnostics and I find that the plug behind the brake booster does not have 12v on the red lead. The yellow lead ranges from 1 - 6 volts when the fan switch is adjusted. Black lead appears to be ground and is ok. If I put 12 to the red lead the fan works correctly. Now my question.

Where does the red lead on this plug get the 12v from? Could this be due to a blown fuse (if not obviously)? After checking both sides of fuse 12 in the fuse box there is no power there whatsover and it looks a little melted on the bottom side. How would I go about getting the 12 volts from the fuse box to the red lead? Can I just get an inline fuse (30 amp) and do the upgrade myself without a MB kit? How do you get into the fuse box to get the power? I have tried loosening the 6 screws I see for the fuse box and cover and it will not open. We have the repairs CD's but they are not helping with my limited electrical knowledge.

Thanks to any and all who can help. This is his first car and he cannot drive it unless he gets some heat. I am sure you all have felt the same as him about wanting to drive the car you just bought. Thanks again in advance.

welcome

use the 'search' feature, a very discussed topic.

http://www.peachparts.com/shopforum/search.php?searchid=175983

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*92 400e 124.034, SOLD

*92 300e 124.030, SOLD

I have a similar problem on my 126 SD, no heat and it is -20 C here today!! not fun but I park facing the sun and it keeps the windscreen clear. How do you get at the bloody heater fan? My problem is not fuses, I checked. Anyone with suggestions?

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The meek shall inherit the earth, the brave shall get the oceans

I understand how often the topic has been discussed. I have used the search option and that is how I found out what I already know (having read every single one of them for the past 40 days). These are very specific questions that have not been answered on this board (at least that I can find). I am well aware of how these boards work and do not mean to take up bandwidth. If anyone can help it would be appreciated. Thanks

There was a mid year change to an exterior 30A , as you already know.
The fuse mod was simply put in parellel with fuse 12 [ 25A]
You have to get to the bottom side of the fuse panel #12, where you will most likely see the wires burnt. If you can clean the feed wire back , hook a new exterior fuse to this feed and splice the other end into the red wire . That will give you fuse protection and feed only when key is ON.
Use heavy stranded copper.
That's it.

Thanks for the info Arthur. I still cannot figure how to get to the bottom of the fuse box. I see on other posts that you have to go through the dash panel on a w126, I hope it isn't that difficult on a w124. I have taken the 6 screws off the top of the fuse panel (2 at the front, 2 at rear of fuse panel and 2 at rear of relay panel) but cannot get to the bottom of the fuse panel. Is there some kind of secret to getting in there? The red wire comes out of the firewall at the rear of the brake booster and the socket that plugs into it appears to go to the resistor pack. Any idea where to find this wire behind the firewall? That would probably be the best place to splice into it. Would it hurt to splice into it on the harness for the resistor pack? The last few questions would probably be mute if I can find out how to get into the bottom of the fuse panel.

Once again, thanks for all the info you have provided.

On my 1990 300E you remove the screws and lift the fuse panel out.

With the battery disconnected, of course!

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2012 E350
2006 Callaway SC560

The panel has to be removed .
The feed wire from the ignition sw to fuse 12 is Pk/Gn.. that is where you want to slice a new fuse holder . From the holder , the draw side will splice on to the Bk/Gn wire .
That will eliminate the fuse 12 . [ you are just cutting the 2 wires to F-12 and subbing a larger , seperate fuse/holder.]
I just have a schematic here , so I am not sure what is entailed to get to the wires , but they should be under the fuse base..

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My schematic shows no resistor pack on 1986 300E.
It shows this to be Transistor Regulated circuit. N/29 regulator with yellow feed trigger voltage from ACC push button controller...which is what you have described ...

Sorry for the wrong designation. When I stated resistor pack it appears that it is the transistor regulated circuit. I am still having problems getting into the back of the fuse panel. Is there anything that states how to get into the bottom of the fuse panel on an '86 w124 to cut and splice those wires. Thanks for the wire colors, once I figure out how to get to them it appears to be pretty straight forward.

Finally have it figured out, what a pain this has been. Near the front of the fuse panel there is one screw in the middle (between the 2 for the cover) that I was not seeing. Removing this screw lets me open the fuse panel to get into the back and the wiring. Once inside the fuse panel I found the problem. Someone had done a jury rig mod for the blower fuse and hid the fuse inside the fuse panel box. Open the fuse holder and viola!!! there is the blown fuse. It was a 25 amp ceramic fuse, so I replaced it with the 25 amp fuse that was in the 12 slot and presto!!!! Works like a champ. I have the actual MB mod coming in and I will do the mod correctly for future service. Thanks to all for your help.

One hint for anyone reading this thread in the future. Before tearing down the car to get to the blower motor. Check the voltages at the plug above the brake booster. This would have saved me about 6 hours and a bunch of busted knuckles. There should be 12v at the red wire, ground at the black wire and 1-9 volts (adjustable with the blower spped control) at the yellow wire. If there is not 12 volts on the red wire, the problem is with the power at the fuse box or fuse block.

The replacement fuse should be 30A.
And your voltage hint is correct for voltage testing , but the thing you really want to do after the fuse/wiring repair is to take an amp draw reading on the red feed . It is common to have worn brushes/bearing in the motor and that
will show as a high draw [ which just makes the burn wire/fuse problem just return in a matter of time , along with burning out the regulator [ very expensive].
The original wiring and fuse were not sufficient for fan load longevity, and the new set-up will hold a normal spec. load, but not if the fan motor draw is beyond spec...
I have also seen some home-made mods that use the red to trigger a high Amp rated relay with direct/fused bat feed to solve the high draw from the fuse box.. the fuse [ #12] can then be brought down to 15A., as this is now just primary relay feed, with the relay contacts carrying the high motor/reg load....
Simular to the relay type set-ups guys use when they rewire for higher output headlamps...

Hi can someone show me where the photos pertaining to the blower fan are located (the photos are referred in the above posts for a 126 car).
Thanks
Dan

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1969 RS/SS Camaro Conv. L-89 Alum. Head 396 375HP 4-spd

1987 GNX #419, 2002 RX300

FS: 1934 Ford Street Rod, Blown 383 $48,500 Firm

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The blower motor is located under the passenger side dash. You have to remove the knee bolster and you should see the blower motor housing. Several screws (4 I think) to remove to get the black cover off and then you will have to remove more screws (4 more I think) and unplug the motor to get it out. It is not a difficult job at all to remove but you have to really contort your body to get too it. If you move the passenger seat all the way back it helps. Some old newspaper on the floor board keeps any old grease, dirt, dust, etc. from getting the carpet dirty.
Good luck - hope this helps.

P.S. - Did you check the strip fuse in the black box next to the actual fuse box? Sometimes it corrodes or develops a crack which will cause the fan to quit working.

benzboy87
thanks for your reply, I am unable to find the other fuse. Can you describe where it is located in relation to the fuse box. Also what does it look like.
Thanks
Dan

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1969 RS/SS Camaro Conv. L-89 Alum. Head 396 375HP 4-spd

1987 GNX #419, 2002 RX300

FS: 1934 Ford Street Rod, Blown 383 $48,500 Firm

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