Help Needed headlights pulsating

[smokin'jay]

i just noticed my headlights, dashlights, markerlights and domelights pulsating. (just getting dimmer for a brief second, repeatedly) it wouldn't start this morning, (one battery tested bad) so i put two new deka batteries this evening. voltage on both batteries seem ok (14.45-14.51 vdc while running) but amp draw seems to jump around from 1.5 to as high as 11.3 while running. truck is warm and batteries should be charged from several mile test drive after battery replacement. truck just back from body shop after minor collision damage. 2000 f-350 4x4 crew cab short bed srw 163k miles 7.3 powerstroke, stock, no chip (yet)

 

[Yooper75]

i just noticed my headlights, dashlights, markerlights and domelights pulsating. (just getting dimmer for a brief second, repeatedly) it wouldn't start this morning, (one battery tested bad) so i put two new deka batteries this evening. voltage on both batteries seem ok (14.45-14.51 vdc while running) but amp draw seems to jump around from 1.5 to as high as 11.3 while running. truck is warm and batteries should be charged from several mile test drive after battery replacement. truck just back from body shop after minor collision damage. 2000 f-350 4x4 crew cab short bed srw 163k miles 7.3 powerstroke, stock, no chip (yet)

I drove a Suburban with this problem and it turned out to be a corroded ground cable to the chassis. They replaced the ground cable and the problem disappeared.

 

[smokin'jay]

checked both ground cables...both tight and clean...amp draw all over the place and volts jump by about 1/2 a volt while running

 

[JLDickmon]

shut the engine off and flip the key back to the "run" position
see if it does it then.

unplug the alternator and start the engine, see if that changes anything.

 

[smokin'jay]

started truck cold (in 30 degree pole barn) started fine. headlights started pulsing, shut truck off, turned key to "on" no pulse. unplugged small 2 wire connector from single altenator, no pulse, battery voltage dropped to 12.05 after running a few minutes, still no pulsating. shut truck off, reconnected alt. battery voltage climbed back to 14.45 slowly and no pulsating at lower voltages...truck has now been running for about 15 minutes, steady 14.42-14.45vdc and a steady 8-12 amps on right positive battery cable. altenator looks after market and is "ULTIMA 01-3680"

 

[JLDickmon]

started truck cold (in 30 degree pole barn) started fine. headlights started pulsing, shut truck off, turned key to "on" no pulse. unplugged small 2 wire connector from single altenator, no pulse, battery voltage dropped to 12.05 after running a few minutes, still no pulsating. shut truck off, reconnected alt. battery voltage climbed back to 14.45 slowly and no pulsating at lower voltages...truck has now been running for about 15 minutes, steady 14.42-14.45vdc and a steady 8-12 amps on right positive battery cable. altenator looks after market and is "ULTIMA 01-3680"

it's the cheap-ass voltage regulator on that reman alternator.
Replacing the regulator only should cure it..

 

[smokin'jay]

started doing it again tonite...i found a listing for a voltage regulator at autozone but where is it located under the hood?? i have a reputable small parts store that i usually buy stuff from but use the web sites for a price guide. it lists for about 60 bucks online and my usual parts store is close.

 

[JLDickmon]

started doing it again tonite...i found a listing for a voltage regulator at autozone but where is it located under the hood?? i have a reputable small parts store that i usually buy stuff from but use the web sites for a price guide. it lists for about 60 bucks online and my usual parts store is close.

It's on the back of the alternator.
You'll need to pull the alternator, and you'll need a Torx driver to change it.

 

[smokin'jay]

thanks...got one ordered today from my local independent auto parts dealer...39 bucks...

 

[smokin'jay]

got my new regulator installed and it seems to be working...thanks for your advice!!