For background, I dug up a couple of pics of the two different styles of instrument panel this model could have had, as mentioned last time.

This is the version that only has indicator lights for most things. You can see how both of the round sectors are used, with the cold and hot lights on one side and the fuel gauge on the other.

This is the type that we have; this one pictured has the optional tachometer in it, and the left side's round area is empty.

Here's what it looks like when you've completely taken it apart:

I'll get into the specifics in a second, but first, a couple of things to note here:

- the old sub-harness for the gauge cluster is in the upper left. You can see it still has the lamp sockets and bulbs.
- the new sub-harness is that coil of multicolored wires in the lower left, next to the alternator. That will need to be rearranged so that the wires route to the correct parts of the assembly, and the ones that go to lights will have to have the sockets attached. All of the stuff required for that is in the wooden organizer on the bottom right, including a little cardboard box of new bulbs.
- those four cardboard tubes just above the wooden organizer are, collectively, the oddest and least expected thing I found in there. I'll show you what they're for in a bit.

For now, let's take a look at some of the individual components.

These are the blanks for the unused round segments. They're just bits of painted sheet metal, attached to what I assume would be the same backing plates the gauges or lights would be attached to in other models that had things in those holes.

(As an aside, I don't know why it never occurred to anyone at GM to put a clock in the unused one on the "full gauges" version of the panel, but it appears that they never did. There was an optional clock available in these trucks, but it was mounted up on top of the dash.)

This is the enclosure that the whole mess goes into, once everything is removed, plus a look at what the speedometer/odometer looks like without the faceplate. 10,664.1 miles, right. More like 210,664.1...

I should look up how to reset the odometer (it's probably pretty easy with a unit this old--they were notoriously not tamper-resistant). After all, we'll have to declare the mileage inaccurate on the registration regardless.

Here's the enclosure after I took some Simple Green and dishwashing liquid to it...

The spots on the inside that still aren't clean are rust bleeding through the paint, I think. I could try to match the color, sand, and repaint it, but I think I'll just leave it alone. We're not making a concours restoration here, after all.

Note the four round holes, two lower left and two lower right, that have the little metal prongs and traces of some kind of black sealant around them? Those are where those four cardboard tubes attach. Literally all they're there for is to isolate the light from four of the many small lamps that come in through the back of the enclosure. I think they were probably originally painted white on the inside, but now the inner color is more of a dull beige.

This shows the three pieces of the front panel, before cleaning. The plexiglas panel has a sheet metal mask behind it, like a clipping mask in Photoshop, that makes the layout come together.

You can get a better idea of how it works from this pic, which I took after cleaning the transparency:

In this shot it's also clearer where the light coming through those four cardboard tubes goes. Two of them are for the directional indicators, and the other two would illuminate those two round red lights. I say "would" because they weren't actually used in this model truck.

This gauge cluster was also used in heavier trucks of this era, and those two lights pertain to things they had that the light-duty trucks like ours never possessed. With some judicious use of a flashlight, we can see that one of them is a "tandem lock" light, which is only used in trucks with two rear axles...

... and the other is an overspeed warning, which is also a dual-axle thing.

I think it's kind of neat that they included these features, complete with the lettered color inserts, in gauge clusters that were never going to be installed in trucks that needed them. I assume GM did that to save costs, since it simplified both assembly and supply--they could just have whichever factory made these make them all the same and put them in whatever trucks required them, without having to worry about whether they were the correct version.

That said, we could use these lights for something else. It would be easy enough to wire, say, the TAND'M LOCK light to the temperature gauge, so it comes on when a HOT condition registers, or the OVERSPEED one to a parking brake sensor. We would just have to remember that in this instance TAND'M LOCK means high temp and OVERSPEED means the brake is on. :)

This is a back view of the instrument panel mask. I don't know why they painted it this way, but that's how it came from the factory.

Notice that the directional indicators weren't customarily green when this was made. I think I might get ahold of some green transparency film and glue it in behind them...

Speaking of things that weren't the colors in 1966 we now expect them to be, the light that comes on when the high beams are on is in the speedometer...

... and it isn't blue.

Last but not least, here are the four smaller gauges, which are built in pairs.

From left to right: coolant temperature, charging system status, oil pressure, and fuel level. From this shot and the pic of the complete unit up top, you can see what I meant last time about how they're really not all that informative. Only the oil pressure gauge is calibrated in any actual unit, and even it only shows a notional maximum value.

One interesting feature of these gauges is that, while the other three are electrically powered and controlled, the oil pressure gauge is entirely mechanical. Instead of an electrical signal coming from a sensor in the engine, it's directly connected via a tiny pipe that literally carries engine oil up to it, exerting said pressure directly on the gauge. Nowadays they generally are electric, but in 1966 that just wasn't a thing yet.

I hope you have enjoyed this somewhat random tour of what's inside a '66 Chevy pickup's gauge cluster and how it goes together. Next shop day, I'll probably be putting it back together and working on getting it wired up. Once it's completely wired and lit, it should just plug into the main wiring harness via that big white connector you can see on the new pigtail in the photo of everything laid out, up above.

--G.
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Benjamin D. Hutchins, Co-Founder, Editor-in-Chief, & Forum Mod
Eyrie Productions, Unlimited http://www.eyrie-productions.com/
zgryphon at that email service Google has
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