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  #1  
Old 01-29-2013, 12:14 PM
winmutt's Avatar
85 300D 4spd+tow+h4
 
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Turn signal fuse keeps blowing. 87 300d

Seems like I have a short to ground that I cannot find. I measure ground to L and R pins in the hazard socket and get 22 ohms or so. I've pulled all the front turn signal plugs and got the same reading at #3 pin on those. At fuse #6 (the one that blows) I get the same 22 ohms from the top. What is confusing to me, I get 22 ohms across + and - battery terminals with battery removed.

Thoughts? This followed an IP swap and some vacuuming in the engine bay. I also found some rat droppings and a half eaten block of poison in the bay as well. (I had left the car outside for a week).

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1991 300D Nearly Perfect
1994 E320 Cabriolet
1995 E320 Touring
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  #2  
Old 01-29-2013, 02:13 PM
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Interesting problem. Rat poison should have more than 22 Ohms resistance.

Suggestion: remove all turn signal bulbs, front and rear. Make sure nothing is touching any of the contacts in the lamp housings and that the wires in the immediate area of the lamp housings all looks OK. Now turn on the ignition and try the turn signal lever. Obviously the turn signals won't work and you should get a bulb-out warning but does the fuse still blow?

If the fuse doesn't blow, you know it has something to do with one of the bulbs / sockets. Add bulbs one at a time until one causes the fuse to blow. There is your problem.

If the fuse still blows you know it isn't related to the bulbs and their sockets. It then could be the turn signal switch in the steering column, the combination relay N10 in the fuse/relay box (included the flasher circuit), the lamp-out warning relay (also in the fuse/relay box) or the wiring in between.

Jeremy
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"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . .239,000 miles My car
1996 E300D (W210) . .313,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . 722,685
"Oh lord won't you buy me a Mercedes Benz."
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  #3  
Old 01-29-2013, 02:39 PM
winmutt's Avatar
85 300D 4spd+tow+h4
 
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Quote:
Originally Posted by Jeremy5848 View Post
Interesting problem. Rat poison should have more than 22 Ohms resistance.

Suggestion: remove all turn signal bulbs, front and rear. Make sure nothing is touching any of the contacts in the lamp housings and that the wires in the immediate area of the lamp housings all looks OK. Now turn on the ignition and try the turn signal lever. Obviously the turn signals won't work and you should get a bulb-out warning but does the fuse still blow?

If the fuse doesn't blow, you know it has something to do with one of the bulbs / sockets. Add bulbs one at a time until one causes the fuse to blow. There is your problem.

If the fuse still blows you know it isn't related to the bulbs and their sockets. It then could be the turn signal switch in the steering column, the combination relay N10 in the fuse/relay box (included the flasher circuit), the lamp-out warning relay (also in the fuse/relay box) or the wiring in between.

Jeremy
So top of fuse 6 and ground should be wide open right?
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http://superturbodiesel.com/images/sig.04.10.jpg
1987 300D Sturmmachine
1991 300D Nearly Perfect
1994 E320 Cabriolet
1995 E320 Touring
2001 Eurovan FOR SALE
1985 300D car, sold and missed.
OBK #42
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  #4  
Old 01-29-2013, 04:07 PM
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?????

Quote:
Originally Posted by winmutt View Post
So top of fuse 6 and ground should be wide open right?
Not sure what you mean. Fuse 6 powers a number of things -- it's wired to S7 the horn, S6 the hazard flasher switch, p4 the outside temperature display, N2/4 the warning module and possible others. But yes, with the ignition off and key out there should be nothing on the load end of Fuse 6. You should not get any resistance to ground -- it should measure infinite on an ohmmeter.

Jeremy
__________________

"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . .239,000 miles My car
1996 E300D (W210) . .313,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . 722,685
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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  #5  
Old 01-29-2013, 04:17 PM
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Fuse 6 also powers the bus bar I believe that is hidden behind the dead pedal, mashed/cut up wires there can cause a dead short.
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  #6  
Old 01-29-2013, 04:59 PM
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Power strip

Quote:
Originally Posted by Zulfiqar View Post
Fuse 6 also powers the bus bar I believe that is hidden behind the dead pedal, mashed/cut up wires there can cause a dead short.
Power strip X30 under the dead pedal is powered by fuses 9, A, B, and C, not fuse 6, according to FSM / ETM.

Jeremy

__________________

"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . .239,000 miles My car
1996 E300D (W210) . .313,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . 722,685
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Last edited by Jeremy5848; 01-29-2013 at 05:04 PM. Reason: Add diagram of X30.
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  #7  
Old 01-29-2013, 05:07 PM
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right - sorry bout that,

need some tea. ..
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1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)
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  #8  
Old 01-29-2013, 08:31 PM
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An old electrician/controls field engineer trick for finding a short:

Use a bulb in place of the fuse. Try a double ended bulb like in the glove box or dome light.

This provides a safe series impedance to help find the fault without hurting things. And it stops glowing when you found the short.
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2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older sonís DD)
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1998 E300DT sold to TimFreeh
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  #9  
Old 01-29-2013, 10:10 PM
winmutt's Avatar
85 300D 4spd+tow+h4
 
Join Date: Apr 2006
Location: Atl Gawga
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Quote:
Originally Posted by jay_bob View Post
An old electrician/controls field engineer trick for finding a short:

Use a bulb in place of the fuse. Try a double ended bulb like in the glove box or dome light.

This provides a safe series impedance to help find the fault without hurting things. And it stops glowing when you found the short.
Dayamn, that is some sage wisdom right there. LOVE IT. (and for once not complaining about the old cylinder style fuses).
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http://superturbodiesel.com/images/sig.04.10.jpg
1987 300D Sturmmachine
1991 300D Nearly Perfect
1994 E320 Cabriolet
1995 E320 Touring
2001 Eurovan FOR SALE
1985 300D car, sold and missed.
OBK #42
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  #10  
Old 01-30-2013, 12:30 AM
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That trick has saved me more times...

You might have to pull the turn signal relay in the relay box, and jump pins 8 and 10 when trying this trick. The bulb may present too much series impedance to allow the turn signal relay to function correctly.
__________________
The OM 642/722.9 powered family
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older sonís DD)
2008 E320 Bluetec (Younger son's DD)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
----------
gone but living on
1983 240D (body to greazzer, engine to t walgamuth)
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  #11  
Old 01-30-2013, 12:37 AM
jay_bob's Avatar
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And according to the ETM, the turn bulbs are not supervised by the external lamp monitor. At least not directly like the other bulbs. The turn signal flasher monitors the bulb current and if it doesn't have the load of 2 bulbs it flashes fast.

There is a tap to the monitor relay from the output of the flasher, maybe this is a special input to the monitor that looks for the fast flash pattern to turn on the warning light?
__________________
The OM 642/722.9 powered family
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older sonís DD)
2008 E320 Bluetec (Younger son's DD)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
----------
gone but living on
1983 240D (body to greazzer, engine to t walgamuth)
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  #12  
Old 01-30-2013, 11:33 AM
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Quote:
Originally Posted by jay_bob View Post
An old electrician/controls field engineer trick for finding a short:

Use a bulb in place of the fuse. Try a double ended bulb like in the glove box or dome light.

This provides a safe series impedance to help find the fault without hurting things. And it stops glowing when you found the short.
That is always my standard when finding a short - old sharpie cases make great self powered line testers too. Excellent part about mercedes is that you can stick banana plugs to test the sockets.
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1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)
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  #13  
Old 01-30-2013, 05:12 PM
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The 1xx chassis is an electrical dream to work on. Except for some bad choices in wire strand counts across hinges, the wires are nice and solid. You can actually maintain the connectors or worst case rebuild the harness with a soldering iron. Or you can do neat tricks like convert from a 4-pin to 5-pin OAT display without having to cut or splice any wiring.

You can actually still buy the housings and the pins and sockets.
__________________
The OM 642/722.9 powered family
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)
2008 ML320 CDI (Older sonís DD)
2008 E320 Bluetec (Younger son's DD)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech
----------
gone but living on
1983 240D (body to greazzer, engine to t walgamuth)
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  #14  
Old 01-30-2013, 11:12 PM
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Quote:
Originally Posted by jay_bob View Post
An old electrician/controls field engineer trick for finding a short:

Use a bulb in place of the fuse. Try a double ended bulb like in the glove box or dome light.

This provides a safe series impedance to help find the fault without hurting things. And it stops glowing when you found the short.
I always do that when looking for a short at any voltage. You do have to be aware however that any load in the circuit will cause the lamp to glow, with it's brightness being determined by the resistance of the load. A dead short will allow the lamp to glow at full brightness, but once the short is removed the lamp will still glow at a lower brightness if there is a load existing on the circuit, like another lamp for instance.
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  #15  
Old 01-31-2013, 01:57 AM
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The lamp test is a neat idea. Seems to me I remember seeing long ago fuse holders with a lamp built in. If the fuse blew, the lamp would glow so you immediately knew which fuse was bad.

Jeremy

__________________

"Buster" in the '95

Our all-biodiesel family
1995 E300D (W124) . .239,000 miles My car
1996 E300D (W210) . .313,000 miles Wife's car
Santa Rosa population 170,685 (2012)
Total. . . . . . . . . . . . 722,685
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970
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