I just bought this 300CD and spent the last few weeks doing all the recommended service and maintenance myself to get it in good shape.

Im nearing the end of my restoration and have a problem with an electrical short.

When the car is on and I'm operating the windows fuse #2 blows. This causes not only the devices listed on fuse #2 to not receive power but it causes the windows and hazards to stop working also.

I had the radio, antenna, clock, visor mirrors, all out at one point and this problem persisted. I also replaced the drivers door switch.

Why are the windows affecting an unrelated circuit (they are on fuse a and b)? Similarly, why is fuse #2 causing the separate window circuits to lose power, once they cause it to blow?

Could I have a frayed window motor wire in the door post? Im duped.

Fuse #2 powers the power windows relay which powers fuse a & b. When fuse #2 blows, all windows stop working.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I replaced the relay behind the cluster with one pulled at the junkyard. Still popped #2. The windows move up and down but if you hold the button for too long after they are either all the way up or down - thats when it blows.

fuse #2 says:
"
clock, trunk light, diagnostic, switch-
over valve seat back arrester, roof
light front + rear, hazard warning
system, autom. antenna, illuminated
vanity mirror, warning monitor
term. 5, (electronic radio)
"
no mention of windows or window relay for #2...?

I'm looking at this schematic and getting more confused. it says they go from fuse 12 but doesn't show the relay or fuses a and b.

what am i missing here?

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i was thinking it could be in the drivers multi switch. there appears to be no ground to the driver side rear window switch (where the sunglasses arm is pointing). is this normal?

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Window motors are not grounded. The window switches reverse polarity to the motors so they can go up or down. You need to look at the wiring diagram for the power windows on 82 or older model years.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Forget the power distribution. It is missing info. You need to look at the diagram for the power windows, which is only found in 82 and older wiring diagrams. With that diagram you should be able to find where the short is.

Fuses a & b are 16 A, but fuse 2, which supplies power to fuses a & b through a relay, is only 8 A. That's why (when there's a short) only fuse 2 blows since it is lower A than fuses a & b.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I suspect the fuse box has been re-wired to power the window ( which windows blows the fuse when you hold it down?? ) thru fuse #2. For a start, you are NOT suppose to hold the button down when the window is at the end of its travel. When the window is at position the current drawn will be so high as the motor is not turning. When that happens either the fuse will blow or the motor will burnt out, take your pick.

This is what I would do to confirm:

1) Remove fuse a and fuse b.
2) Check any window still operates, if any one does then the wiring had been changed. Make a note on which window operates.
3) Put a back in and see which window operates.
4) Put b back in and see which window operates.

You can get a W123 Haynes manual for $20 and it has the wiring diagram. May be the window relay is by-passed.

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

1. Pull the window relay first, if the windows still work, wiring is not original.

2. Pull fuse #12. If windows still work, wiring is not original. Work the windows and see if fuse #2 still blows.

3. Pull fuses a, b. If windows still work, wiring is really messed up.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

The windows should work just fine with Fuse #2 not installed. Mine certainly do.

Or did you mean to say Fuse #12, again?

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

hi again,
first of all thanks for the input

just to clarify:
*talking about all four windows working normally and all four individually popping #2 when reach all the way up or down
*also pops #2 if you roll more than one window at a time
*i had a friend sitting shotgun blow the fuse on accident yesterday so its not from operator error its definitely looking like a wiring thing. (ahem tangofox you were right)


pulled fuses a and b... windows still worked and blew #2 when reached all the way up or down.

pulled relay... windows still worked and blew #2 when reached all the way up or down.

pulled fuse #12... windows still worked and blew #2 when reached all the way up or down.

the rabbit hole just got deeper.

going to hunt down a haynes manual in my area.

What should happen is that the thermal switch in the window motor opens, preventing the other "picks" from occuring. Ever notice that the window won't immediately reverse after being fully opened or closed? Then you hear a faint "click," and then the window then operates normally.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

I am offering a scenario to the OP on why fuse #2 blows all the time with window switch pushed down for a while. #2 fuse is red and is rated 16A nominal. It is a hefty fuse, unless the OP put a white one in there. If the 'thermal' switch in the window motor is working then why the fuse would blow unless the thermal switch breaks at a higher current. It is never good practice to hold down the switch for a long timw. So don't tell be what 'should' and 'should not' happen. Actually I do not notice anything except someone try to lecture me. You are better than that!!

__________________
Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

That would be my first place to look.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

unplugged:
trunk light
switchover valve - vacuum transducer
switchover valve - boost pressure aneroid
roof light front + rear
visor mirrors
radio

still blew

that leaves:
clock
diagnostic
switchover valve seat back arrester
hazard warning system
antenna
warning monitor term. 5

aside from the clock and antenna i dont know how to disconnect these to check for short.

not even sure what these are let alone how to disconnect:
diagnostic
switchover valve seat back arrester
warning monitor term. 5

thanks for your replies

Per the 1982 Electrical Troubleshooting Manual, power to operate the windows should not go through Fuse 2. The hot-at-all-times wire to Fuse a & b is terminated on the upstream side of Fuse 2. Any chance somebody re-engineered your fuse box and connected the window power on the wrong side of Fuse 2?

According to the 1982 manual, that would be Fuse 12.

Even a Ford engineer would know better than to design a circuit like that!!!

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.