Mega Fuse or Alternator Issue?

[chrisnin]

Hello, just wondering if anyone can help with the location of the mega fuse in a 2004 Explorer XLT. Had a battery die last week... gauges started flipping out, warning lights came on, stereo died, and car just quit running... thing was acting like it was possessed. So I changed the battery. New battery died 2 days later with same symptoms. I jumped it and rand down to Advance Auto and their diagnostic tool said the alternator was bad. I put in a brand new alternator, and after putting it in, the battery light came on. Battery is dying again, and when I put the multi meter on the battery with car running, it's not getting current from the new alternator. It does not jump to over 14 volts as it should. I read that the mega fuse could cause this issue, but I can't find the damn thing anywhere??? Anyone have these issues or know where the mega fuse is located? I also looked for the alternator fuse in the owner's manual, and I didn't see anything dedicated to the alternator/charging. Should I be looking at another fuse? Thank you in advance for any help on this!!!

 

[boominXplorer]

In most 2001 and newer there is no actual fuse for the alt. They have fuse able links that look like heat shrinked area in the power wire going from the alternator. Have you checked for 13+ volts at the stud on the alt? If your getting nothing there you probably have a bad alt out the box.

 

[chrisnin]

In most 2001 and newer there is no actual fuse for the alt. They have fuse able links that look like heat shrinked area in the power wire going from the alternator. Have you checked for 13+ volts at the stud on the alt? If your getting nothing there you probably have a bad alt out the box.

I have not tried that... I'm assuming you just touch the red lead to the stud and touch the black lead to a ground with the engine running?

 

[boominXplorer]

I have not tried that... I'm assuming you just touch the red lead to the stud and touch the black lead to a ground with the engine running?

Yes. If you get 12.0-12.6 the wire is good, Alt is bad. If you get 13+ there is a break in the connection, Alt is good.

 

[chrisnin]

Yes. If you get 12.0-12.6 the wire is good, Alt is bad. If you get 13+ there is a break in the connection, Alt is good.

10-4... I'll check it out. Thank you for the advice. If the wire is the issue, is there some chance that a mega fuse is placed on the wire going from the alternator to the battery and shrink wrapped in heat tape?

 

[chrisnin]

10-4... I'll check it out. Thank you for the advice. If the wire is the issue, is there some chance that a mega fuse is placed on the wire going from the alternator to the battery and shrink wrapped in heat tape?

Battery showed 12.52 and Alternator showed 12.50... I'll go exchange the new alternator and see if it was just DOA. I'm hoping that's all it was!

 

[imp]

Hello, just wondering if anyone can help with the location of the mega fuse in a 2004 Explorer XLT. Had a battery die last week... gauges started flipping out, warning lights came on, stereo died, and car just quit running... thing was acting like it was possessed. So I changed the battery. New battery died 2 days later with same symptoms. I jumped it and rand down to Advance Auto and their diagnostic tool said the alternator was bad. I put in a brand new alternator, and after putting it in, the battery light came on. Battery is dying again, and when I put the multi meter on the battery with car running, it's not getting current from the new alternator. It does not jump to over 14 volts as it should. I read that the mega fuse could cause this issue, but I can't find the damn thing anywhere??? Anyone have these issues or know where the mega fuse is located? I also looked for the alternator fuse in the owner's manual, and I didn't see anything dedicated to the alternator/charging. Should I be looking at another fuse? Thank you in advance for any help on this!!!

@chrisnin

I am looking at the 2004 wiring diagrams. Not sure what you mean by "mega fuse". A number of things things may affect the alt. not pushing current to the battery. The main feed wire to the battery is protected by a series "fusible link" in the in the line from the alternator through the junction box, to the battery If that link opens, it should be visibly browned, discolored, burnt-looking, not smooth. There are two more fusible links, in series with each other, which connect to the junction of the first at the battery junction box, rearward of the battery. You can see them there. A short-circuited alternator can burn out any or all of these fuse links. They consist of a short length of wire several inches long, coated with special insulation. They are NOT fuses as you would think of a "pull-out" and replace fuse, but are permanently wired-in. If blown, they must be cut out and a new link soldered in.

Open the cover of the fuse box; at the left end (front of vehicle) there is a nut holding two terminals which have the fuse links leaving the terminals downwards, and away. One is a thick red wire leading directly to the + battery terminal. I believe the main fuse link is built into it.

A fuse in the vehicle fuse block, driver's side, fuse 21, 5 Amperes, feeds the voltage regulator system, and activates the warning lamp. I believe if that fuse is blown, the alternator will not charge, so check it first. If blown, and it blows upon replacement, some where a short circuit exists; I don't expect that will be the case.

Finally, before doing any of the above, you might check at the alternator itself whether voltage is present while engine is running. Measure between the main, big terminal and ground. If voltage is present at low level, say less than 12 volts, good chance one of the fuse links is blown. imp

 

[chrisnin]

@chrisnin

I am looking at the 2004 wiring diagrams. Not sure what you mean by "mega fuse". A number of things things may affect the alt. not pushing current to the battery. The main feed wire to the battery is protected by a series "fusible link" in the in the line from the alternator through the junction box, to the battery If that link opens, it should be visibly browned, discolored, burnt-looking, not smooth. There are two more fusible links, in series with each other, which connect to the junction of the first at the battery junction box, rearward of the battery. You can see them there. A short-circuited alternator can burn out any or all of these fuse links. They consist of a short length of wire several inches long, coated with special insulation. They are NOT fuses as you would think of a "pull-out" and replace fuse, but are permanently wired-in. If blown, they must be cut out and a new link soldered in.

Open the cover of the fuse box; at the left end (front of vehicle) there is a nut holding two terminals which have the fuse links leaving the terminals downwards, and away. One is a thick red wire leading directly to the + battery terminal. I believe the main fuse link is built into it.

A fuse in the vehicle fuse block, driver's side, fuse 21, 5 Amperes, feeds the voltage regulator system, and activates the warning lamp. I believe if that fuse is blown, the alternator will not charge, so check it first. If blown, and it blows upon replacement, some where a short circuit exists; I don't expect that will be the case.

Finally, before doing any of the above, you might check at the alternator itself whether voltage is present while engine is running. Measure between the main, big terminal and ground. If voltage is present at low level, say less than 12 volts, good chance one of the fuse links is blown. imp

Thank you very much. I did check the 5 amp fuse and it was good. I took out the new alternator that I had installed and exchanged it for another new alternator. Problem solved! It appears that the first new alternator was DOA. The guys at the auto parts store said that it has been known to happen. Thanks again everyone for the help on this!

 

[Number4]

The plug with multiple wires in it which goes to the alternator, sends and receives signals from the PCM. Those signals tell the PCM voltage needs and I turn the PCM dictates how much the Alternator puts out.

Typically, a bad wire here will turn on the battery light. But could also keep the alternator from charging if it's not sending or receiving the proper signal.

A lot of alternator brands are crap. Make sure you have the new alternator tested before bringing it home (may have been fine leaving the factory, but who knows how many people dropped it before you got it.)
Have your battery fully recharged and tested before connecting the two items.

Perform a voltage drop test. (Google it.)

 

[imp]

The plug with multiple wires in it which goes to the alternator, sends and receives signals from the PCM. Those signals tell the PCM voltage needs and I turn the PCM dictates how much the Alternator puts out.

Typically, a bad wire here will turn on the battery light. But could also keep the alternator from charging if it's not sending or receiving the proper signal.

A lot of alternator brands are crap. Make sure you have the new alternator tested before bringing it home (may have been fine leaving the factory, but who knows how many people dropped it before you got it.)
Have your battery fully recharged and tested before connecting the two items.

Perform a voltage drop test. (Google it.)

@Number4 Question for you: If battery is out of car, on floor of shop, and you are testing various electrical problems, and connect jumper cables to the battery from the battery terminals in the car, and lighting was poor, and you got a big spark upon connecting the second clamp, thinking that was the charging current for the hair bags, how long before you realized the mistake of backward connections and yanked off one of them, would it take to fry one of the 3 fusible links to the alternator?

5 seconds? 10? More? Less?

(I did it). Felt like an asshole!

 

[Number4]

When you count out 5 seconds, it seems like a really long time, considering.

 

[imp]

When you count out 5 seconds, it seems like a really long time, considering.

@Number4

The damned things are OK, believe it or not. Hooked all the dangling wires back up, or out of the way, started up, voltage jumped to 14.4, no sweat. Tomorrow I start chasing an Oxygen Sensor Heater issue.