Light Pulsate

[md993a]

I have a 2003 Excursion with 7.3L motor. Last week, all the lights(interior and exterior) started to pulsate real fast. I had both batteries and alternator checked by two different shops, they all checked out fine. Any suggestions as to what could be causing this problem?

[jesilvas]

I have the same dang thing. I know it's the alternator. I've been meaning to check it myself, along with it's amperage output. Mine is a Duralast with a lifetime warranty. I talked to them, they tested it and this person actually kinda new what she was doing, except for the batteries being in parallel . But she said if it kept having problems, bring it back.

[md993a]

Thanks, I find it interesting that I had two independent shops check the alternator and both said it was operating fine. Are your lights flickering fast(2x per second)?

[jesilvas]

Hadn't really counted, but you can definitely tell they are pulsing around once a second or so. Actually, it might be even faster so yea. The girl did say it was putting out 14.x volts, which we both found kinda weird.

[jesilvas]

Ok, SOOO.
Readings right off the alt were:
Voltage - Varied from 14.5xV to 14.97V. Seems high to me, not sure what that would mess up, if anything.
Amperage - Went from almost 0A all the way to 40A really fast. So fast, I almost couldn't read what numbers it was showing.
Other than the alternator, obviously, being the main suspect, I have had something sqeaking forever. I think it's either the AC pulley bearing, OR my tensioner is too loose allowing the belt to slip on a pulley and squeak. If it is slipping on the alternator too, then that would cause problems I assume.

[md993a]

Thanks for the replies. I ordered a Heavy Duty alternator. Will see if that fixes the problem. I was also told by someone who works in Ford Service there is a module behind the fuse box that could cause this symptom as well.

[wy.miner]

I'm having the exact problem with the same results when I have the alt. checked at the parts store. Did the new heavy duty alt. fix your problem

[jesilvas]

I finally had to replace my tensioner.
Didn't fix the pulsing. It's the alternator. Probably specifically the voltage regulator.

[md993a]

Thanks, I replaced the alternator and it fixed the problem.