One question I did have regarding bulb placement/operation:
Low beam - only top ones ON
High - top and bottom are ON
I don't want to cause confusion down the road saying the top or bottom if they are backwards.
Below is just about everything I think I know about the square body quad headlight setup - and I
know this will cause confusion.
1. Start off with the easy stuff- this is how the headlights are designed to look when illuminated,
On low beams:
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On high beams:
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2. When equipped with halogens, the original GM part numbers for the upper/low (dual filament) and lower/high sealed beams were: 16532129 & 5930567, respectively. The P/N for the high beam seemed to be consistent as noted above - 5930567 (50 W).
On the other hand, the low beam part number varied depending on the wattage combination. There were 3 sealed beams with dual wattage ratings that were generally used: 35/35, 40/45 & 40/60.
3. The sealed beams were more commonly known by their ACD (AC Delco) model numbers. In the case of a 1986 C/K truck, they were sold as H4652 (40/60 W) & H4651 (50 W):
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4. These particular sealed beams are classified as type 2A1 & 1A1. The first digit (1 or 2) refers to the number of filaments incorporated within the lamp. The alpha character and the final digit defines the dimensions of the glass at it's largest point. The A1 class sealed beams are 100 mm X 165 mm:
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5. As mentioned above, while all the sealed beams within a particular classification must have the same physical dimensions, they can vary as to the rated wattage. In 1986, GM spec'd the sealed beams used in their quad headlight design to be 40/60 W for the low beams and 50 W for the high beams (i.e. the 4652 & 4651):
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6. One aspect of GM's quad headlight design that confuses people is how the dual filament/low beam operates under dimmed and undimmed conditions. The higher wattage filament (60 W) is actually the one that is energized when low the headlights are dipped (on lows). When high beams are switched on, power is secured to the 60 W filament and the 40 W filament is energized along with the single 50 W in the high sealed beam. Like this shown below.
Lows:
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Highs:
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7. The next issue that comes up is wiring. Specifically, how the 3 wires are supposed to be connected to the low beam's terminals. With the high beam, it doesn't matter which way the connections are made. Either wire can be on either terminal and the lamp will still illuminate correctly.
But on the dual filament low beam it is critical to proper operation that the high beam, low beam and ground leads are connected exactly right. A 4652 sealed beam that is correctly mounted and wired looks like this:
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It looks like it's upside down and crooked, but that's how a 2A1 is supposed to be:
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If you look lower down in the picture above, you can see that the terminals in the 4651 (high beam) are at the same angle as those on the low beam. The high beam has an A1 designation and so it's indexed counter-clockwise as well.
Here is a closer look at the upper/low beam:
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That images are from my old truck that was kept completely stock. They match up with the federal government standards for 2A1 & 2E1 sealed beams:
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I'm color blind so there is no apparent difference in color between the high and low beam (lt grn & tan) leads. But I can see that the black ground wire is in the upper left corner of the triangle. That is the opposite of how most wiring diagrams depict it - and how the terminals are layed out for every other dual filament sealed beam - except the 2E1 type. This page shows the geometry of the 2 B,C & D classes:
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If you look inside a halogen 4652 sealed beam, you'll see the type of lamp commonly used today encased in the glass shell. The small bulb - containing the filaments - within the rectangular glass shell is called an envelope. That is the area that contains the halogen. On a vacuum sealed type beam, there is no small, inner bulb. The filaments are exposed and the entire shell is under a near perfect vacuum.
