I have a 2000 Expy EB with the 5.4. While it is running, all of the interior/exterior lights pulse. Alt, bat, voltage reg all new. There is a plug near the firewall just to the right of the battery. It comes from the voltage reg and then goes into a wiring harness and I have no idea what else it connects to. If I unplug it, the pulsing stops and there seems to be no other effect on the vehicle. It still charges and everything works that uses power. But I don't want to just unplug something not knowing what else it might go to. Any assistance would be greatly appreciated.

 

Plug it in and be done with it. That is the voltage feedback for the regulator circuit. Without it, the regulator will continually "hunt" for an output voltage.

 

When it's plugged in is when there is a problem. If it has to be plugged in, how do I make the pulsing lights stop?

 

Ah, misread that...

Okay, need to identify the plug. How many wires and what are their colors.

 

Not sure of the colors at the moment but it's 2 wires.

 

Ok, just got a close look at the wires. They are: orange with a blue stripe and green with a brown stripe.

 

Does the charging (battery) light come on during the initial bulb test when the key is first turned from OFF to RUN?

Have you checked fuse F11 in the under hood fuse box?

If necessary, do you have a voltmeter?

 

Battery light died come on. The fuse isn't blown, but it does look like it has gotten a little hot. I don't have a voltmeter, but I can tell you at the parts store the voltage reg tests bad on the vehicle but good off of it.

 

Does, not died

 

Get a meter. Next steps involve voltage readings.

 

rectifier bridge in alternator is bad

alternator generates an AC voltage and the diodes turn it into DC
if the diodes are shorted, the pulsing is from the AC voltage getting onto the DC side so as the power alternates ( sine wave) you get pulsing as the voltage rises and lowers.

if the diodes are open, then the pulsing can be from voltage drop as there will be no voltage from the alt during that cycle of the sine wave.
this will happen to quickly for a digital meter to see unless you have a scope meter and can watch the frequency/waveform.

replace the rectifier bride ( made up of 4 diodes) in most cases these are built in to the alt and you need to replace the entire alt.

yes, even if the alt is new you can still have defects....

 

oh ya- that plug I believe is for the voltage regulator.

the regulator controls voltage to the rotor (the coil of wire in side the alt that spins) by controlling the voltage you control the magnetic field and hense the voltage generated in the main coil ( the stator)

so when you unplugged it you shut down the alternator and you were just running off of the battery and no output from the alt equaled no pulsing.

 

That's likely your problem, excessive resistance in the battery sense/feedback circuit. This was very common in the Contour/Cougar 2.5L world. Ford finally issued a TSB back in 2000 to address it (TSB 00-25-6). The TSB essentially makes permanent the following diagnostic step:

To test, back probe the orange/light blue wire at the alternator and connect it directly to the alternator B+ output. If the pulsing stops, you've correctly identified the issue.

It is unlikely that it's a problem with the regulator or diodes. If it were ripple for a shorted or open diode(s), it would be so rapid that you'd never see it in the lights due to the higher frequency of the AC generated by the alternator prior to rectification. It's most likely that this pulsating is only several times per second.