Who needs strobe lights? AKA Headlights flickering on high-beam

[Jmclendon]

Hello all,
We've got to stop meeting this way.

So, here I am driving along being all cocky about no-longer alerting the neighbourhood that I can't shift into first gear properly, when I think to myself "self, it's getting a bit dusky out. You love this truck. Can't have anyone running into you (as if he could go unnoticed). Maybe it's best you turn your lights on."

A couple of minutes later, the headlights are flashing like it's a scene out of Saturday Night Fever (I'm guessing there was some disco flashing in that? Don't judge me, it was before my time).

I had a bit of a play and it looks like low beam is ok, the tail-lights and the indicator aren't effected. But, after a little bit in high-beam, the head lights flicker on and off and I can hear a bit of what I'm assuming must be alternator whine coming from under the hood. Turn the high beams off and the whine stops, as does the flickering.

Based on the symptoms, I'm thinking it's not enough juice getting to where it needs to go? Maybe? However, the alternator is brand new, as is the battery. I can't say it's been on many long drives as of late. Just a bit around the block and whatnot. So could it be that I've started it too many times without driving enough to give the alternator a chance to top the battery up?

Thoughts?

[FetchMeAPepsi]

Could be a short in the high beam wiring or the secondary lights. To eliminate the bulbs themselves I'd pull the high beams out and try it to see if I get the whine again. If it whines, it's shorted.

If not, maybe one of the bulbs is drawing too much current. Corrosion on the posts? These are all glass bulbs so be careful. I cut myself pretty good getting my old one out because I dropped it on the ground and it shattered. Bulbs are cheap (about $14 USD) so at worst you'll have a couple of extra bulbs.

The next thing might be the step switch. I've never heard of one going out, but they're pretty universal. You can pick one up at the local auto parts store.

[jagarra]

The high/lo step switches can cause problems, especially since they are mounted in the floor and get a lot of crud splashed on them.

[Jmclendon]

If it was just shorting somewhere, would it still cause the load noise in the alternator? I guess I had assumed if it was a short somewhere that the lights might play up, but that there wouldn't be any alternator whine.

I know nothing about electrical magic though, so I'm happy to be educated LOL

[FetchMeAPepsi]

Originally Posted by Jmclendon

If it was just shorting somewhere, would it still cause the load noise in the alternator? I guess I had assumed if it was a short somewhere that the lights might play up, but that there wouldn't be any alternator whine.

I know nothing about electrical magic though, so I'm happy to be educated LOL

Absolutely. If it's drawing from that little kick button straight through to the floor it may be pulling all the amps it can pull just to get the lights burning. Same with any decent sized wire touching the body. If it was a small wire shorting it may just burn through instead of drawing a heavy load.

[Jmclendon]

Well that all sounds fun LOL I'll take apart the button and see if there's anything within my capability to diagnose.

For some reason electricity has always been one of those things that just doesn't make sense to me. It's looking like I need to make myself learn a bit more..... If for no other reason than to occasionally save myself the pain of paying $110 an hour to get an auto electrician to fix minor problems and whatnot.

[FetchMeAPepsi]

Electricity isn't too tough at a basic level. You just think about the negative post being the sea, and the red post being a river. One always wants to flow to the other. Wires are just channels the river runs through and it'll always take the fastest route. Corrosion on the wires or connectors are rocks in the river, slowing things down or damming them up altogether.

That's my "dumb country boy" take on it. I can't do advanced resistance and ohm or amperage stuff off the top of my head but some guys get off on that stuff so if you run into any of that you can ask for help.

For the switch, if it's wonky just replace it. Auto parts stores (O'Reilly's? O'Wallaby's? haha!) carry them. They were used for a ton of years.

Good luck!

[jimjaz]

Sounds like a short in the wiring on the high beam wire- check the wire feeding the high beam circuit from the hi-lo switch to the connection at the grille. Two grommets that this (and other wires) pass through; one at the firewall into the engine bay, and the other through the radiator core support. The grommets could be missing/damaged- look closely for rubbing on the wire shielding and bare wire exposed, and shorting to ground. The strobe effect I am dreaming that this could be the problem. Turn on your high beams with the key off- strobe effect gone? If the high beams are bright and steady with the key off and strobing while running, then you most likely have a short. With the engine running (vibration) the wire could be shorting to ground intermittently causing this strobe effect. You could use something non-conductive like a round piece of plastic (weed-eater type trimmer string comes to mind) that you could push into the bottom of the hole carrying the high beam wire, lifting the wire off the bottom of the hole and if your strobe effect goes away, that is where the problem is.

Also don't forget to check and clean your fuse connections at the box as I mentioned before if the above does not pan out. There could be a lot of rocks in the river (corrosion) that will limit current flow. O'Wallaby's? Now that is funny!
Good luck!

[6066gmcguy]

There is a whole section on the website that deals with a lot of this, its called "Lighting & Electrical Projects &/or Demons in Your GMC".

Start with the page, "Some Good Wiring Advise"

As for the headlights, there is a circuit breaker built into the headlight switch, these get old and will trip making your headlights look as if you installed a flasher in the system, you may need to replace the main headlight switch. There is not a fuse on the headlights.

after a new switch you mite want to try the "Headlight Relay System" to keep the power draw down on the switch.

[Jmclendon]

Thanks for the advice and the info. Hopefully I'll be able to make some sense of it.

Worst comes to worst, high-beams aren't really that important LOL.