Wiring problem - Keep Blowing a fuse (W124)

Timster · 09-07-2008, 09:20 PM

Hi There.

Fuse number 3 on my W124 250TD (Estate) keeps blowing.

It's the fuse which controls the back right light, the dashboard lights and the front headlight wipers.

As soon as I turn on the headlights it blows. (It's an 8amp fuse)

What I need you to tell me is:

a) Why!
b) How to fix it

or

a) What to do with my voltmeter to isolate the fault.

I've changed all the bulbs and it's not them. Although I can't vouch for the one behind the dash, as I really want to avoid removing the dashboard if I can help it.

Thanks in advance.

Tim

mattkh · 09-07-2008, 10:36 PM

Hi
Disconnect the plug to the back right light and the front headlight wipers.
Now with a new fuse in turn the dashboard lights.
Is the fuse blown?
If not, then plug the back right light. Turn the light ON. Is the fuse blown?
If not, plug the front headlight wipers and turn them ON. Is the fuse blown?

Dieselman · 09-07-2008, 10:38 PM

It's most likely to be either a chafed wire leading to the rear light or the headlamp wiper has water in or is duff.

With the lights off and disconnected use your meter in continuity mode and connect the black lead to Gnd and the red lead to the tail lamp connection. You should have infinate resistance but may have a short to Gnd.

Reconnect one by one until the fault manifests iself.

grober · 10-07-2008, 12:05 AM

My money is on the headlamp wipers shorted due to water =very common due to their location I would start your process of elimination there.

Timster · 10-07-2008, 09:41 AM

Thanks all for replies so far. Going to start pulling bits out after work today, hope I can isolate the fault nice and quickly!

Any more suggestions, keep 'em coming. Will let you knwo how I get on.

Ian B Walker · 10-07-2008, 10:45 PM

This found on a customers car.

Water

09-07-2008, 09:20 PM	#1
Timster Hardcore MB Enthusiast Join Date: Jun 2008 Location: Scotland Car: 1993 S124 300TD Posts: 120	Wiring problem - Keep Blowing a fuse (W124) Hi There. Fuse number 3 on my W124 250TD (Estate) keeps blowing. It's the fuse which controls the back right light, the dashboard lights and the front headlight wipers. As soon as I turn on the headlights it blows. (It's an 8amp fuse) What I need you to tell me is: a) Why! b) How to fix it or a) What to do with my voltmeter to isolate the fault. I've changed all the bulbs and it's not them. Although I can't vouch for the one behind the dash, as I really want to avoid removing the dashboard if I can help it. Thanks in advance. Tim

09-07-2008, 10:36 PM	#2
mattkh Member Join Date: Apr 2008 Posts: 42	Hi Disconnect the plug to the back right light and the front headlight wipers. Now with a new fuse in turn the dashboard lights. Is the fuse blown? If not, then plug the back right light. Turn the light ON. Is the fuse blown? If not, plug the front headlight wipers and turn them ON. Is the fuse blown?

09-07-2008, 10:38 PM	#3
Dieselman Hardcore MB Enthusiast Join Date: Jul 2003 Posts: 19,310	It's most likely to be either a chafed wire leading to the rear light or the headlamp wiper has water in or is duff. With the lights off and disconnected use your meter in continuity mode and connect the black lead to Gnd and the red lead to the tail lamp connection. You should have infinate resistance but may have a short to Gnd. Reconnect one by one until the fault manifests iself.

10-07-2008, 12:05 AM	#4
grober Hardcore MB Enthusiast Join Date: Jun 2003 Location: Perth SCOTLAND Car: E220 COUPE Posts: 8,968	My money is on the headlamp wipers shorted due to water =very common due to their location I would start your process of elimination there.

10-07-2008, 09:41 AM	#5
Timster Hardcore MB Enthusiast Threadstarter Join Date: Jun 2008 Location: Scotland Car: 1993 S124 300TD Posts: 120	Thanks all for replies so far. Going to start pulling bits out after work today, hope I can isolate the fault nice and quickly! Any more suggestions, keep 'em coming. Will let you knwo how I get on.

10-07-2008, 10:45 PM	#6
Ian B Walker Hardcore MB Enthusiast Join Date: Jun 2003 Location: Kirkham Car: 300-24, E220 Coupe, E220 saloon, 190D Posts: 7,912	This found on a customers car. Water

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