Fuse No. 24 "ELEC B" keeps blowing

[Kazza]

Hi guys,

 

I have a problem whereby Fuse No. 24 (7.5a) labelled "ELEC B" is repeatedly blowing. I have studied the Electrical section of the Service Manual for the car and I know that this fuse protects many different circuits and most of them also interact with the Smart Entrance Control Unit. Now before I go on a wild goose chase.. I'm just wondering if anyone has any ideas on the best place to start or things to try before I need to go chasing down all the circuits to find a short?

 

Here are some observations;

• The fuse oddly seems to blow every 48 hours or so.. it seems relatively consistent.
• The circuits which are also connected through the ignition switch do operate again when the key is in ignition and turned to ACC or ON e.g. power locks
• I have not managed to locate what circuit is causing the fuse to blow by operating them.. e.g. headlamps, interior lights, power locks etc.

 

I'm not sure if its a particular circuit on the fuse or the SECU itself thats to blame... any help to get me started would be most appreciated.

 

Cheers!

 

K

[Mr_Reverse]

Does it blow while just sitting, or while driving? Does your truck have electrical add one? 

These gremlins are a PITA to track down at times. Sometimes you have to do a visual inspection of the wiring to track it down. 

Last year had a F150 that kept blowing a fuse that I couldn't find the problem in traditional ways. I wound up going into the harness and cutting the splice where the 6 different circuits were connected near the fuse. I then wired in 6 fuse holders and labeled them. With fuses a size smaller in each of those holders waited for one to blow. I don't recall what was bad ultimately, but that did manage to isolate the problem area. A few weeks ago, I asked the owner if it was still fixed and he said no problems, so it worked. 

[Kazza]

Hi Mr_Reverse..

 

Firstly to answer your questions, it seems to blow the fuse while sitting, not driving. And no additions to the car that I know of.

 

I have since had a look at the three connectors going into the SECU and noticed damage/melting of pins no. 49 and 50 on connector M123. Pin 49 goes directly to fuse no. 24 (the one that's blowing) and pin 50 is the battery saver for interior lamps which is connected to the circuits of all the interior lighting and the door switches.

 

These two wires looked to almost be fused together near the SECU connector so i carefully separated them and re-insulated them separately. The fuse is still blowing.

 

Would this possibly narrow the problem area down at all?

Perhaps it's the SECU since the wire going to the fuse melted? 

...Or maybe the damage to the wire itself is causing the short?

.....Or the issue is with the interior lamp / door switch circuit due to the damage on the battery saver wire?

 

Its hard to say which wire fused to which...

 

Thanks in advance for anymore input.

 

Regards,

 

K

[Mr_Reverse]

Not sure without doing some research on what all the SECU runs and affects. If you can still get into the car and operate it safely with the module unplugged, might want to try that for a couple days to see if the fuse is still blowing. If the fuse stoops blowing, then you found the problem. The way it is looking from what you have said here, I would suspect a failure inside the module is causing your problems

[Kazza]

1 hour ago, Mr_Reverse said:

Not sure without doing some research on what all the SECU runs and affects. If you can still get into the car and operate it safely with the module unplugged, might want to try that for a couple days to see if the fuse is still blowing. If the fuse stoops blowing, then you found the problem. The way it is looking from what you have said here, I would suspect a failure inside the module is causing your problems

 

The SECU is connected to about 15/20 different functions in the car. There are 3 plugs. My plan is to do as you hinted at - unplug each plug one at a time to disable different functions and see if the fuse blows. If it doesn't this will narrow me down to 4/5 functions and I can divide and conquer from there. I will probably need to pull specific pins on one plug though as it houses the ground and the wire to the fuse in question. Will provide an update.