98 Silverado electrical issues

[John in WI]

Lately when deiving my truck at night, I notice the headlights going dim and then bright again. I first checked the alternator and it was pushing 14 volts at high idle, but only 9 at low idle. I replaced it with a new alternator that runs at a steady 14 volts, but I'm having the same problem. The lights are nice and bright at driving speed, but then go dim when I let off the gas or hit the brakes. The battery is less than two years old.
Am I missing a voltage regulator or something simple? Does anyone have some tips?
Thanks!
JW

 

[Brute 23]

Check the battery no matter what age it is.

Make sure all connections are good and not corroded up or loose,,, especially grounds.

Assuming that you have a connection for trailer lights that would be the next place I go. Those plug in Ts that you buy at wal-mart and stuff for like $20 just go bad some times and make crazy things happen.

 

[Legacy38464]

Check the battery no matter what age it is.

Make sure all connections are good and not corroded up or loose,,, especially grounds.

Assuming that you have a connection for trailer lights that would be the next place I go. Those plug in Ts that you buy at wal-mart and stuff for like $20 just go bad some times and make crazy things happen.

Another place to check is the actual switch itself they sometimes go bad and cause similar happenings and then go dark...

 

[cfpinz]

Check the battery no matter what age it is.

Make sure all connections are good and not corroded up or loose,,, especially grounds.

Assuming that you have a connection for trailer lights that would be the next place I go. Those plug in Ts that you buy at wal-mart and stuff for like $20 just go bad some times and make crazy things happen.

Another place to check is the actual switch itself they sometimes go bad and cause similar happenings and then go dark...

My old 87 F350 had a problem similar to that. But the fuse panel had broken loose from the mounts and was flopping around under the dash. It melted the headlight switch connector when it landed against it, then got the wiper switch. I knew I smelled something.

Do not assume an alternator is okay just because it's new, you get a dud from time to time. I looked on napa's website and couldn't find any exterior voltage regulators for a truck of this year so it must be internal. That would have been my first bet. Electrical problems are the worst to find.

cfpinz

 

[Brute 23]

It could be a ton of things but you have to start with the basics and get them out of the way and checked off.

Once that is done then you can start getting into ALL the other stuff.

 

[Bullbuyer]

I have the same make/model truck with similar problem. I was driving along and the dang thing just died - I mean dead! Eased to the side of the road (obviously without lights, power brakes or power steering) - thing was just like it didn't even have a battery in it. Come to find out the positive terminal was loose - tightened it and headed down the road. It has backed off a few times since and that problem I don't how to correct - its not like you can put lock tight on a battery connector.

 

[Calman]

You need to rule out the most simpilist things first. I would start with the cables and battery.99% of the time it will be a loose connection somewhere.

Cal

 

[BusterBrown]

I had a 98 Silverado, same thing happened, then got worse, started dying like mentioned above. I finally found that the positive battery cable, although looked like new on the outside, was totally corroded to bits on the inside. I found it by cutting away at the red rubber cover at the battery terminal side. I cut away all the corroded part and put one of those clamp on battery clamps on it. Fixed! :lol: I found it by checking the voltage at the battery, then at the fuse box on the fender well on the driver's side engine compartment. I hooked the VOM to the AUX. terminal with clips then wiggled the cable and noticed the voltage fluctuating. :shock:

 

[larryshoat]

It could be any of the stuff mentioned hear, but if none of that works out.
Those alternators get current from the PCM trough that orange wire hooked to the alternator. We had one with a bad computer that did that. I would wire a small light to that terminal and put it somewhere I could see it and watch it while your driving.

Larry

 

[John in WI]

Those are all excellent tips, and I thank all of your for sharing them. I should clarify that it's the headlights that keep dimming on me. Tonight I disconnected the electric brake - no change. Then I swapped batteries - no change. I checked the trailer lights and all appears tight. I pulled the alternator and will take it in for a test tomorrow. I'm hoping they'll exchage it.
One thing I find humorous about this is that 25 years ago I could just about judge the speed of my vehicle by the intensity of my headlights. We were always tightening belts, replacing alternators and regulators, or cleaning out the sockets for the bulbs.
Now I get a little flicker and I begin to panic. I've become spoiled.