'87 with Dual headlights. Only 1 pair work for Hi/Low beams?

[87ChevyR10]

This is kinda bizarre, the top pair of HL's function as both Hi and Low beams. Sometimes when I switch between the 2, I get no lights at all. Is this a HL wiring harness thing, HL switch, or what?

Thanks!

 

[chengny]

First check would be that the lower sealed beams are good. They only come on when high beams are selected. They use just 2 terminals (50 watts). To test, just use a battery charger.


If they're okay, check the front lighting ground points.

Left:

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Right:

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Next, I would pull the H/L dimmer switch (hi-Lo beam switch) and check it for operation.

You seem to already know the operation of the two different sets of H/L's. But if somebody else doesn't, it goes like this:

Low beams selected - Bottoms off. Only low output filament (35 watt) of top sealed beam is energized.

High beams selected - Bottoms come on (50 watts). Low output filament of top lamp is turned off - high output (50 watt) is turned on.

These images explain better.

Low beams:

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High beams:

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[87ChevyR10]

Nope, mine don't do that. Even though the beam looks brighter with highs on, only the top pair work.

Thanks for the input!

 

[chengny]

Sounds like the dimmer switch is working - the uppers are changing over to high beams.

They don't actually look that much brighter on highs, especially in daylight. To see the full effect it needs to be dark out - and you need to be at about the level of the headlights. Move back and kind of squat down, then have someone switch between highs and lows.

If the tops are switching from high to low the problem is not the switch. Did you check to be sure that the lower sealed beams are good? Do they light up when you attach a battery charger tothe terminals?

If they check out as okay, the problem must be in the wire that connects the top high beam to the lower beam.

There should be a light green wire that splits off and feeds both the top and bottom lamps. Follow it back from the bottom and be sure the splice is good.

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[MrMarty51]

My Haines manual does`nt show the quad headlamps system, so I might be incorrect with this information.
I switched my 93 to the rectangular bulb quad system, My dims would go off when the brights were turned on.
To fix this, I used the brown wire for a signal wire to a relay I installed, then from the other side of the relay I run a light green wire back to the low beams.
Now when I turn on the bright headlamps both dims and bright lamps stay on.
I attached the relay under the black cover, passenger side firewall, from that position a + battery connection is easy and is`nt too far of a run to the dim bulbs wiring on the RH side.
I did a sort of a write up but I can not remember if it is within another headlight thread.

 

[87ChevyR10]

I found this thread again after replacing my hi/low beams and thought I'd take another look into the matter. I plugged my volt meter into both hi-beam only plugs and the voltages are erratic. It'll sit below 1 volt and then jump to 9+ volts. I'll have to get into the wiring and check those splices. Sounds like one or both are not secure. The grounds are good.

Another thing, as I was trying to disconnect the passenger side hi-beam plug, one of the bulb tabs came off with the plug. As I was trying to remove bulb, the plastic alignment piece broke that moves the lamp up and down! So, this bit is on hold until I can get this fixed.

EDIT, might be a while before getting the alignment assembly from LMC. Less than $2 for 1, yet they want to slap on another $8 for shipping and handling! Screw that! It's not even leaving the state to get to me!