I might have to give my Excursion a formal name. In the last year, I have now been through 3 alternators. The first one was the one that came on the truck and appeared to be OEM. It gave up the ghost, and I replaced with a local rebuilder's product that was recommended. That one started putting out 15.7 volts and fried all my LEDs throughout the truck. In addition, it cooked all the insulation about 6 inches up on the 4AWG "hot wire" coming off the back of the alternator. I yanked it and took it back to them. They rebuilt it again, and pro-rated the repair. They said "everything" had failed inside it. 6 months later, that rebuild died. It was putting out 10.5 volts when I yanked it and went to get a new unit from Advance (CarQuest brand). That one lasted about 2 months. Same thing...putting out low voltage again. When I yanked it, it was down to 11.7 volts.

So, now I have a Lifetime warranty unit from Autozone since I have paid so much for alternators over the last year. This one fails, I just take it back and get a new one.

I am working on finding the problem. After putting the newest victim on the X today, I let it idle for a while. I had to charge the batteries overnight, and I wanted to make sure they were taking a charge. Within 30 minutes, the alternator and the "hot wire" were getting VERY hot. This was one of the symptoms with the other alternators before they went out, so I am thinking there is something seriously wrong with the wiring on my truck. Brand new alternator is putting out 13.1 volts shortly after install. Right after install, it had been putting out 13.7 volts. So, in 30 mins it dropped .6 volts.

Well, I don't particularly want to fry another alternator and go through that song and dance again, so I started digging into the wiring on the truck. I have previously checked everything I could and never found an obvious problem. All the grounds are solid, and none of my positive cables are grounding out. Everything ohms out as it should. I have no parasitic draw, either. I have noticed the batteries "boiling over" all the time since this alternator fiasco started two years ago. I will routinely find some battery acid coming out the top of the batteries, but not a whole lot. Looks like they are overcharging? Not sure on that one. When I check voltage on the running alternator (the last two anyway), I get a difference of .1 volt. Example: 1. red lead to "hot wire" on back of alt/black lead to alternator case = 13.1 volts 2. red lead to postive battery terminal and black lead to negative battery terminal = 13.0 volts. I then take the red lead to the "hot lead" of alternator and the black lead to the positive battery terminal and I get .14 volts difference. So I have a voltage drop somewhere in the system of .1 volts. THAT IS SIGNIFICANT!!

So, in digging into the wiring, I find this:


I have a Eureka! moment and I think I may have found my problem! The fusible link is blistered and feels very mushy inside like it may have burnt up. Questions is what caused this? Age? Bad component somewhere drawing too many amps? Starter going bad? I have no idea yet, but here is what I did to fix the link.




















The picture below should read "4AWG from the ALTERNATOR"











Ford no longer carries/repairs fusible links according to my local dealer. However, he said they get people come in from time to time with older Ford diesel trucks looking for one, so they have a roll of it behind the counter. He was nice enough to cut me two pieces @ no charge. That was nice of him, since I almost never have a good experience with them. No one in town carried any fusible link bigger than 14AWG. I would have had to order some online and wait.

So, before replacing the link, the alternator was putting out 13.1 volts and was too hot to touch. Also, the "hot lead" off the back was hot (again). After replacing the fusible link, I started the truck and let it run for a while. The alternator is now putting out 14.1 volts at idle. The alternator did not get too hot to touch in about 30 mins time, and the "hot lead" didn't even get warm. Time will tell if this is/was the problem, but I would really like some ideas on why this happened or is happening. In addition, maybe someone has experienced this before on their 7.3L?

 

The fuseable link you replaced is known as fuseable link "J" on the Ford wiring diagram. It is meant to protect the batteries from a failure of the rectifier in the alternator. It probably blew when your first alternator died. With it blown the output of the alternator (if it is healthy) is forced to go through the regulation line which is a much smaller wire. Thus the heat and voltage drop you were seeing. This is why when you replace an alternator it is a good idea to put a dc current tong on the charge output when you are done (though most people don't because the tool to do so is expensive).

 

You are talking about a DC current clamp? I have a good one. I have never found a high current draw yet while checking the output on the alt with it. Most I have found is 65 amps with everything on. I have not checked it while starting yet to see what the starter is pulling.

 

Here is something to consider. I was going to do a separate thread but thought this might help as well.

Went to bed that night, next morning both batteries were dead. As the batteries were only a year old I put them on the charger and started looking for a problem.

Parasitic drain for the ecu runs about .1-.3 amps which is normal. I saw .8-1.0 amps being drawn with the meter which of course was high. Now I had to find the source of the drain.

Pulled fuses, traced circuits etc.

What I found was while checking the alternator, it was getting hot at the voltage regulator inside the alternator. This on a cold motor not running. Additional test confirmed I was getting voltage on the exciter wire to the alternator with the key OFF. This of course is NG.

Here's why that happened.

I installed a fake flashing LED in an existing hole when I moved my TS tuner switch. (PO put the switch in a bad place visually.) The wiring instructions called for the unit to be hooked up with one wire going to a constant 12v source and the other to go to a 12v source when the key was on.

Followed the instructions exactly. Light worked perfectly with the key on or off as promised.

Because however of the way the LED is wired it was backfeeding milliamps of voltage back thru the key off wiring and energizing the voltage regulator circuit.

Once I took the LED out of the circuit the drain dropped to normal on the amp meter and there was no longer any voltage at the exciter wire on the alternator.

Unfortunately the backfeed also killed the alternator. This within 12 hours.

I have not but will now hook the led up with a relay and run it to ground with the key off.

Check your exciter circuit with the key off and make sure there is no voltage there.

 

When a fuseable link blisters like the one in your picture it usually means that at least one of the legs has blown. With one leg blown you have 65A going through a single #10 which will make it hot (though not as hot as you describe). If both legs had blown (as I suspect) then all of the charge current from the alternator goes through the self regulation diode (most alternators have these not sure about ours as I haven't had to replace mine so I haven't disected one of ours yet) making it very hot and through the small gauge wire that normally kick starts the alternator from the battery making it even hotter. Alternator output drops with an increase in temperature so this becomes a self reinforcing problem thus the decrease in output you see as the unit gets hotter and hotter. Long story short you probably fixed it by replacing the fuseable link.

 

Nicmike,
Nice write-up. Reps sent!

 

Excellent thread and fix with the wires!

In light of it and just to make sure the are to snuff I found and ordered some wire to do all the trucks around here.

 

Great Info! My stock 110 Amp alternator just crapped out, it was only putting out 11.5 volts on the scangauge, so I replaced it with a Bosch AL7606N 135 Amp Alternator. I am going to be checking my fusible links just in case, but right now everything looks good at 13.5 - 14.0 volts steadily after the glow plugs are off.

 

So I checked the amp draw on the starter today. I got 275 amps for a split second while it started (my truck starts right up). This sound right to you 7.3L guys?

 

I use a 250 amp fast acting fuse between my alternator and the battery. Alot more reliable than a link. A good ground from the alternator to the battery is a must!

 

Mike, nice post. I tried to rep you, but seems like I've liked another one of your posts too recently. Bumping anyway, because not only is the info useful, it is extremely well presented. My favorite pic was how you drew the path of the alternator wire snaking it's way across the top of the engine through the jumble of wiring harnesses that otherwise hide it's path like a maze in a cornfield. Nice post, nice tips, and nice presentation.

 

Fuse links are just low cost fuses the manufacturers use to save money.
They can be replaced with marine grade circuit breakers.
In our 2002 the main cable from the battery to the main fuse panel goes forward, along the top of the radiator support, back along the left fender to a terminal block near the firewall. There is no fuse in that line until the terminal block.

 

The ring terminal you were unable to find may be sourced at a car audio stereo shop. I have purchased and used them to add ground wires on other vehicles. Also I believe some have mentioned on here having grounding cables made at a welding shop so another option.

Great information and tips.

 

The ring terminal you were unable to find may be sourced at a car audio stereo shop. I have purchased and used them to add ground wires on other vehicles. Also I believe some have mentioned on here having grounding cables made at a welding shop so another option.

Great information and tips.

 

My Autozone-lifetime-warranty is on the way out...

The saga continues. It didn't even make it 9 months.