87 R1500 Quad Headlight Question

[WFarm]

After driving 200 miles home last night I decided to look into headlight upgrades for my 87 R1500 truck with the quad headlights. But after referring to my shop manual I‘m not sure what’s going on.

I have 2A1 upper lights and 1A1 lower lights, which is what the manual says is correct. On low beam, only the uppers are on, which is also correct. But on High beam, all 4 lights are on. The shop manual says that only the lower lights should be on.

This truck is pretty much unmolested and the wiring harnesses seem intact and original. I am leaning towards the headlight switch itself. Could a faulty or incorrect switch cause all 4 lights to be on?

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[RecklessWOT]

Sometime over the last 36-37 years someone could have rigged it so all 4 stay on when Hi-beams are on. It's pretty common. I always planned to do that to every square I've owned (all have been quad lamps) but just never got around to it. I wouldn't be worried about it, no downside really just better lighting. Unless if you're looking for a 100% original unmolested show quality rig or something, otherwise I'd just accept the free upgrade and leave it as is

 

[PrairieDrifter]

I was always under the impression all four headlights were on when high beams are on and yes only the top lights for low beam. My wiring seemed all factory and that's how mine work. Other than I swapped the low beams to the low lights because I'm lifted.

 

[WFarm]

Sometime over the last 36-37 years someone could have rigged it so all 4 stay on when Hi-beams are on. It's pretty common. I always planned to do that to every square I've owned (all have been quad lamps) but just never got around to it. I wouldn't be worried about it, no downside really just better lighting. Unless if you're looking for a 100% original unmolested show quality rig or something, otherwise I'd just accept the free upgrade and leave it as is

Thanks. Based on this is there a common way this is done such as installing a different switch or doing a wiring mod?

 

[Craig 85]

I had an '87 K20, '87 K30 and an '88 C20 Suburban all when they were under 10 years old and totally stock. All of them only the uppers will light with the low beam. All 4 come on with the high beam. That book is wrong for an '87.

 

[WFarm]

I had an '87 K20, '87 K30 and an '88 C20 Suburban all when they were under 10 years old and totally stock. All of them only the uppers will light with the low beam. All 4 come on with the high beam. That book is wrong for an '87.

At this point I have to agree. Hopefully the manual doesn’t have a lot of mistakes like this.

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[Craig 85]

At this point I have to agree. Hopefully the manual doesn’t have a lot of mistakes like this.

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I haven’t seen that book since I sold my K20 in 1991 to buy my first house. FYI the 89-91 Square Bodies and GMT400s do work that way.

 

[WFarm]

Do work which way @Craig 85 ?

 

[Craig 85]

Do work which way @Craig 85 ?

As you describe in your first post, although those are mounted horizontally. Either the low beam is on or the high beam, but not 4 at a time.

 

[RecklessWOT]

I had an '87 K20, '87 K30 and an '88 C20 Suburban all when they were under 10 years old and totally stock. All of them only the uppers will light with the low beam. All 4 come on with the high beam. That book is wrong for an '87.

On my '87 Suburban, or the '87 GMC longbed Sierra I previously owned, only the lower bulbs were on when the hi-beams were activated. My '84 K5 was the same way but if we're talking '87s, I've personally had two of them that did not light all four bulbs on HI. I always wanted to change it, just never got around to it

 

[WFarm]

I am on a quest to figure this out. I had ordered a new headlight switch with knob and rod (LMC P/N 30-2673) but the rod was shorter than the one I removed and it would not work. Makes me think the switch is incorrect.

 

[Craig 85]

To add to this, I had an 80 C20 3+3 in the early nineties I did a front clip swap to an ‘85 and have had two other ‘85s including my current one. All 3 lit 4 bulbs when the high beams were on.

 

[59840Surfer]

As a California retired Brake/Lamp/Smog Inspector --- I can shed some light on this --- sorry for the pun ..........


The various states either approved or didn't approve the quad lights from GM for a while --- California being one of them --- for a while anyway.

There will be some that light up all 4 in the HIGH mode and some that will power up only 2 in that mode.

Low beam has always been the function of the upper quads - and those with dual filaments in the upper quads could potentially be able to be used if they don't already do so.

I'd bet that there aren't any cops that'd know the way they worked - especially in the mid-1980s anyway! They won't know if you are pre-approved or not.

I run 4 LED headlights (see my avatar), the uppers are LOW Beam and then all 4 come on for HIGH Beam.

 

[59840Surfer]

I am on a quest to figure this out. I had ordered a new headlight switch with knob and rod (LMC P/N 30-2673) but the rod was shorter than the one I removed and it would not work. Makes me think the switch is incorrect.

I remember this problem as I worked on these vehicles when they were still pretty new.

At the moment, I don't remember the answer --- but I THINK it was a manufacturer's option to use the long or the short pins, but they were switch-matched in that a short shaft won't work in a long switch, but a long shaft will work in a short switch.

If the shaft is too long, the knob used to stick out a bit more but it functioned.

Hmmmmmmmmmm... am I remembering that it was the thick/thin facia on the switch bezel that made a difference?

I need a 2AM epiphany.