I have a 1999 Suburban 350. Recently all the lights have started to "pulsate" .?

check 4 a bad ground first off clean ur battery posts then check ur grouns if no probleam found u might find that ur battery may have a internal short try a new battery if u have one good luck

does the speed of the pulsation change

is it quick or bright for a few seconds then dim for a few

my first thing to try would be the alternator/regulator

i did have a ford that was charging at about 18volts and the regulator was switching on and off so the lights would go bright to dim every few seconds. we burnt out 2 regulators before we found the problem in the alternator

it's a bad voltage regulator in the alternator. probably have to change out the entire alternator. most newer units are not serviceable. I buy the lifetime warranty units from autozone and keep a couple of wrenches in the glove box.

How about at night? Do the lights change brightness as a function of rev's. You may have a bad voltage regulator.

Check for bad ground.