So just bought an 2001 Excursion XLT 3 days ago! Truck only has 43k. The motor is 6.8 V10. So driving home the other night I noticed all the lights inside and out are flickering!! No battery light at yhis time. So here's what I did so far had the battery and alternator tested and everything passed. I've read some forums and heard the alternator may pass and still could be the issue... so bought a new one well even with the new one no luck. BUT if I unplug the alternator while running the lights no longer flicker. Please any direction of info will be greatly appreciated.

 

Try this with the alternator running:

Get a jumper cable, and put one end of the black lead on the alternator case, attach the other end to the negative battery terminal. See if the flickering goes away. If this problem only exists when driving, make a cable to run from the alternator case to the negative battery cable. If this solves the problem, you need to clean all your grounds in the engine compartment.

 

Thanks I actually gave this a shot last night with no luck problem still occurring.

 

How fast is the flicker? A flutter like looking through a moving fan or a slow up and down in intensity?

Does the frequency change with engine speed?

In addition put an analog (not digital!) voltage gauge across the battery terminals and see whether the needle is twitching with the lights and what voltages you read.

 

Flickering like looking though a fan would be a good description. It does not slow down or speed up with the increase of speed. Today on the way to work the voltage gauge dropped and lights all dimmed. This is the first time the battery light started to flicker too.

 

I'd look at the ground connection for that negative battery cable. Also what kinda shape are battery cables in?

 

This symptom is usually caused by excessive resistance in the battery sensing or "feedback" circuit. The excessive resistance causes the regulator to overshoot its output, then it pulls back the voltage and the process repeats due to the over-correction. The apparent symptom is a pronounced flickering in the lighting systems, especially so when it's cold outside.

It's pretty easy to troubleshoot.

Connect a jumper from the alternator B+ terminal to the alternator's "A" input(Orange/light blue wire in connector C153a). This jumper bypasses the normal sensing circuit wiring that goes over to the starter relay on the firewall and then back to the alternator via its own fuse link.

Report your results. There are other possibilities but this needs to be checked first.

 

The cables are in great shape due to the truck having very low miles. The ground from the negative to the frame by the started is solid as well.

 

Go check what I suggested...

 

01Ford, He is talking about the small connector on the back of the alternator, not the big, 4 gauge, B+ wire on the lug on the back of the alternator. If your grounds are good, you have a problem with the voltage reference (feedback) coming from the computer. He gave you good advice in his post.

 

Sorry projectsho89 didn't see your post that reply wasn't to you. I will try this thanks for the great info.

 

I apologize for the late update but I did the jumper wire as advised and it worked!! How do I make this repair perminant? Should I run a new wire? Thank you very mucb

 

Can I just run I new line to the battery with a in line fuse??

 

In a perfect world, you'd figure out the particular segment of the circuit with the fault and repair/replace that segment. Yo can use your improvised jumper to bridge segments and see which one has the high-resistance.

I've highlighted the charge-sensing circuit in the attached drawing. I'd focus on the segment that includes "Fuse Link C" as my primary suspect.

 

No. Under moderate loads the alternator is constantly turning off and on to avoid overcharging the battery. If left on all of the time it can lead to the battery exploding. Which I have seen first hand.

If you don't want to make a proper repair then you could use a stand alone voltage regulator made for cars built before the 80's. I don't know whether that will affect the computers but at least things won't explode.