lights/gauges pulsing

[mmterrill]

im having an issue with the lights pulsing sometimes pretty bad. what would cause this besides an alt? ive already replaced that and it still does it. is there a negative frame mount that could be corroded? any ideas would be great. im afraid it will go too high and fry something not to mention it screws with my eyes at dark lol.

 

[downer]

do you have access to a volt meter? it will be a big help and may point to the voltage regulator.

check the voltage at battery with key off. should be 12. if under 12 battery should be load checked at parts store or similar.

start engine, turn the headlights on to put some load on system. check voltage at battery. should have 13-14 volts and steady. if you have 12 volts, then alternator or regulator are failing.
if the voltage is swinging drastically,is over 14, or under ~12.5 it would point towards either alternator or regulator again.

you can check grounds with a voltmeter. with engine running check if there is any voltage between the engine and body, body and frame. just put one probe on engine (carefully, it's running) and the other on the body. check multiple points. if the meter is showing voltage (over a few tenths) then it's time to check grounds. they will corrode in time.

 

[adsm08]

Also check for AC voltage at the battery with the engine running. Pulsing lights is usually a sign of AC voltage in the system. On a vehicle system anything above .3 is too much.

Excessive AC voltage can only come from the alternator. The alternator produces AC voltage, and then uses a series of diodes to rectify it into DC voltage. If those diodes aren't working correctly, and letting stuff bleed back in the wrong direction, AC voltage gets into the line.

If you bought a reman alternator they frequently don't get the regulator or rectifier replaced.