Blown 40-amp alternator fuse?

RAMIRDM1

MEMBER
2005 HONDA CIVIC
1.3L
4 CYL
2WD
AUTOMATIC
156,000 MILES

Hello,

My issue is a blown 49-amp alternator fuse. Replaced battery as originally thought that was issue. Battery totally drained after a day. Researched and decided to replace alternator. All has been well for two weeks, so I thought that fixed it. Suddenly one day at car wash, the car decided to quit running. No dash light or inside light, but had headlights were still working. Looked into engine compartment fuses and found the blown 40-amp fuse (had copper side terminals that screw down). Looked at inside fuses as well, all were good. What I did notice was the fuse that was in there had the copper wings cut down to fit. I found all the newer 40-amp fuses are too large and in order to fit need to be altered. I called Honda dealer to ask if they’re specific fuses to Honda and he stated no. Not sure where to look to find the short, which I assume it is. I’m no mechanic as a friend helped me replace the alternator. Any help/insight would be appreciated! Thanks

4 Replies

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

There are a few things that can cause the fuse to fail. It could be just from age. Here is the thing. I looked through the wiring schematic to locate the fuse you mentioned. I only see 80-amp and 10-amp related to the charging system. I attached the wiring schematic below for the charging circuit. So, you have a reference.

Pic 3 shows the under-hood fuse box. Did I highlight the correct fuse? That is the one that is 80-amp and distributes battery voltage

If that is the one, please confirm the amperage on the fuse. Also, disconnect the black wire to the alternator and isolate it so it can't short. Then, replace the fuse. If it doesn't fail, reconnect the alternator to see if it does. If it does, the short is in the alternator.

Let me know what you find.

Take care,

Joe

See pics below.

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Tuesday, August 30th, 2022 AT 7:32 PM

RAMIRDM1

MEMBER
3 POSTS

Joe, thanks for the quick reply. It is the 40-amp fuse that keeps blowing, see pic. It is located in bottom right of fuse panel in engine. The 80 amp you highlighted is good still, just the 40-amp associated with the alternator is my issue. Strange that it ran well and then decided to give up the ghost? Thoughts? And thanks!

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Wednesday, August 31st, 2022 AT 6:46 AM

RAMIRDM1

MEMBER
3 POSTS

Sorry that 40-amp fuse is for the ignition! Thought I read it as for alternator. Any help would be appreciated.

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Wednesday, August 31st, 2022 AT 5:44 PM

JACOBANDNICKOLAS

MECHANIC
109,747 POSTS

Hi,

Okay, that is fuse 20 in the schematic, but it shows it to be a 50a fuse. See pic 1. If that is correct, that sends power to the ignition switch where it is distributed when the key is in the acc or on position. See pics 2 and 3. In pic 3, I circled the letter D because it jumps to a different page on the schematic (pic 4 below).

Take a look at what that fuse powers. I want you to first check those fuses. Also, confirm there is no power to them when the key is on or in ACC.

If the fuses are good, chances are the issue is at the switch itself, but we need to confirm. I say the switch may be the issue because the fuses that are powered should have failed first if a specific component failed. They are smaller in amperage.

So, I need you to remove all of the fuses in the interior fuse box. Replace the 40 (or 50) amp fuse. Replace it with what is presented in the vehicle and not what the schematic is indicating.

With the smaller fuses removed in the interior fuse box, turn the key on. Does the 40-amp fuse fail? If it does, the problem is likely at the switch. If it doesn't fail, start replacing one of the interior fuses one at a time to see which one causes it to fail. Note: the last pic I attached shows the inside fuse box and which fuses to remove. In addition, confirm there is no evidence of melted plastic, wiring, or anything that could indicate a short circuit behind the box.

Let me know what you find.

Take care and let me know if you have questions. Also, please confirm I selected the correct fuse you indicated.

Joe

See pics below.

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