2002 F350 7.3

Ok, So today I hooked up my 5th wheel trailer. I stepped out to lock the hitch and plug in the power cord but when I got back in, my battery light was on. OH CRAP! My alternator just took a crap on me!!! At least that was what I initially thought. I had just got back from a 500 mile trip yesterday and was thankful it didn't happen while on the road.

Well, since I follow Gibbs rule 39, there is no such thing as a coincidence, I decided to do a little bit of trouble shooting first and felt that there may be some issue with me hooking up the 5th wheel. I pulled the fuse panel and sure enough, the 20 amp Trailer charging fuse was blown. Made the 2 mile trip to O'reilly's and bought a new fuse. What I did notice was that after I pulled out of the drive, the battery light went out and stayed out. Once I got the fuse at O'reilly's, I got back in, started her up and the light was back on. Took off down the road and the light went out. Got home, changed the fuse, started her up and the light never came on other than during the normal start process.

So my question is, does any esle know what "other" situations can make the Bat Lights come on like this other than the alternator going out and a bad battery and possibly a ground issue as I have read on other threads.

As a side note, I was curious as to what caused this fuse to break other than maybe being old??? The 5th wheel is still hooked up to shore power but I have never had an issue plugging the truck to it in the past like that. And just for the heck of it, I pulled out the owners manual for the camper and it does not caution about connecting the truck to the camper while shore power is connected either. Any comments on this?

 

You don't say what year vehicle it is so I can only stab in the dark.

On Pre-01, there is a harness which runs from the valve cover to the under hood fuse box. Do a wiggle test. They tend to short at either end.

 

UPDATE!!!

Well, maybe it is my alternator??? I am totally confused now. I just went out and started her up and the battery light was back on. I still had the fuse panel off and I looked at the suspect fuse and it appears to be good. I did notice that I had the parking lights in the on position for about 20-30 minutes, so I turned them off. I pushed on the accelerator and noticed the light extinguished at around 1500RPM's. I kept it there for about 5 seconds and the battery light started flickering and then full on. I increased the RPM's to around 1900, light went back off and then shortly after that it started flickering again. It was at that point, I got a little disgusted because I had the day off to where I could work this problem out thinking that I did have it solved but now its back and the day is almost over and I have other things going on.

I don't have a scanner, but can an autoparts store plug in and check the alternator without removing it?

 

They should be able to do a charge/start test with it in the truck. Sounds like bad or worn brushes To me. I've seen brushes in alternators last anywhere from 50 miles to well, forever haha

 

Usually when the alt light comes on you lost one of the diodes in the alt, and it will still charge till the other 2 go. Thats why they call it the diode trio, Having the camper plugged in to shore power and plugging in the camper should make no difference, but somewhere in your camper your shorting the charge circuit to ground, that's popping fuses. you really need to check the charge wire in the camper, since the problem is only when you plug in the camper, could be right at the 7 way connector, I have seen chaffing of wires there. how are the batteries in the camper, low or dead? a low battery could easily pull 40-50 amps to recharge, but your limited to 25 amps because of the wire gauge and length. You just cant put a bigger fuse in and make it better. You have to find out why the batteries are draining. Make sure your land line charger is working, you may be plugging it in but the on board charger is not charging the batt's. the truck only tops off the batteries, not deep charging. A carbon pile tester would be the tool to use but there only at professional shops, so a DVOM will have to work. Test the voltage at the batteries when your plugged in from 120 volt. looking for 14.6. A load test on the batteries would be a good idea too.

 

Here is the testing process. Note in the Schematic, you MUST have 12v after the 10 Amp Fuse (which causes the light to extinguish) and the Voltage regulator to "Close".

echo=on
Tools: DVOM, Carbon Pile Tester or Similar Device, Hydrometer.

BATTERIES:

Charging system problems often come to you as a "no-start" complaint. The battery will have discharged and the starter won't crank the engine. The first step is to test the battery and charge it if necessary.

No-Load Test:

Voltage Percent Charge
12.60V - 12.72V 100%
12.45V - 12.71V 75%
12.30V - 12.44 V 50%
12.15V - 12.29V 25%
(Readings obtained at 80°F)

ALTERNATOR:

1. Place the (+) DVOM Lead on the B+ Post of the Alternator
2. Place the Ground (-) DVOM Lead on the Alternator Mounting Bolt
You should see > 12.9vdc Minimum and 14.3 vdc Maximum.
3. Perform the same tests placing the (-) DVOM Lead on the Negative Battery Cable on the Battery, reading differing >.5vdc indicates corrosion or a loose connection which requires cleaning and.or repair.

RIPPLE VONTAGE:
1. Ripple Voltage Ripple voltage or (AC voltage) can be measured by switching your DMM to AC and connecting the black lead to a good ground and the red lead to the "BAT" terminal on the back of the alternator, (not at the battery).
2. A good alternator should measure less than .5 VAC with the engine running. A higher reading indicates damaged alternator diodes.

ALTERNATOR LEAKAGE TEST:
Alternator Leakage Current to check alternator diode leakage, connect the multimeter in series with the alternator output terminal when the car is not running. Leakage current should be a couple of milliamps at most; more often, it will be on the order of 0.5 milliamps. Use care when disconnecting the alternator output wire; make sure the battery is disconnected first.
echo=off

 

Well, just got back from the auto parts store and $180.00 poorer. The alternator was on its way out. Was only outputting 10.5-11 volts. I spoke with a friend and ran it by him and he thinks that the camper probably caused the problem. He feels that the batteries (2 of them) may be low or the charging system on the 5th wheel has an issue. I am towing this thing back home on Saturday and once home, I can properly diagnose the camper so he suggested I just disconnect the charging wire and tow it on home. He did say that the only thing I would probably lose is the emergency disconnect brake if my batteries are dead, which I don't think they are they just may be low. I don't have my simpson meter with me here on the road and I don't feel like buying one just to see where the bats are when I have 3 sitting on the bench at home. But on the bright side, I know what I will be doing in the morning with a cold engine and I caught it now before it left me stranded on the side of the road somewhere between Texas and Colorado.

 

Man, thanks. A picture is worth a thousand words. It is stored away for future use.