Just bought my 89 IROC a few weeks ago. Have most of the mechanical issues resolved and now am switching gears to electronic ones. With the headlights on they (along with the interior dash lights) pulse at a fairly steady rate. My first guess was a bad alternator (which tested good). I've heard of people replacing the alternator any ways and having success.

Anyone out there with the same problem or an idea of where to start?

 

I also had a similar prob does it only do this at idle? and does it have an underdrive pulley? i wld also check all engine or chassis grounds and may even add some jus 2 cts

 

Hey Mike,
It does it at idle and highway RPM's (2500).
I'll have to check the pulley... Is there a page with what diameter it should be?

 

Tell us more about the pulsing. What frequency/period does it pulse at? Does the frequency change with engine RPM? With vehicle speed? Does it pulse only with the engine running?
Does the pulsing frequency change with more load on the electrical system? (fans, A/C)
Can you tell whether the pulsing is discrete (sudden "jump" in brightness) or ramped (slow change, as if you turned a dimmer switch)?

 

Well here is a good one for you guys. I apparently fixed my issue.... My driver's side low/high beam lamp burned out. Replaced both it and the passenger's side and the pulse has gone away. With that being said I did notice that the driver's side lamp was a bit dimmer than the passenger's side when I bought the car a few months ago. So I am going to assume a bad ground or some type of internal "short" within the lamp???

 

I had a lose ground wire on the passenger fender-inner fender area that was lose and caused me all sorts of problems. It wasn't that lose either but you could spin it with your hand with a little force.