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Hi guys, I recently bought some new switches to replace my old worn AC/recirc/hazzard/defrost switches. However, I ran into a snag: I did not know there were different generations of switches. I think the switches I have are older generation, with 4 vertical connector pins at the rear, whereas the newer generation switches have 5 horizontal connector pins at the rear.



The old switches are on top, the new on the bottom. This is from the rear, where the connector pins are.



Here, we see the internals of the rear of the connector, the top showing the new and the bottom showing the old. They are oriented the same way: notice the new ones have pins parallel to the camera's vision while the pins on the old connector are perpendicular.



The housings. Top = new, bottom = old. Note that the lower 3 left pins on the new housing are common.

I'm thinking of adapting the older connectors to the new switches (ie. replace my old connector receptacles with matching new connector receptacles). After doing some tests and reviewing the switches from their insides, I believe the old switches were basically two switches in one: light and function switch, hence the 4 pins: one pair of contacts for each light and function. The new switches have a row of common pins, thereby reducing the 5 pins to an actual 3 pins. The pins are common when the switch is closed. This means that there is one or two pins for light (discussed below) and function is the 3 pins that become common when closed. This seems simple enough.

However, there is a resistive element inside the new switches I'm not sure about, which seems to generate different resistances for different switches. The new switch has labeled pins, the old switch does not. When the AC switch is open, pins 5 and 4 (non-common pins) reads 143.5 ohms, when closed pins 5 and common (pins 6, 7, 8) reads 13.5 ohms. For the recirc switch, pins 5 and 4 reads 177.5 ohms when open, and pins 5 and common read 48.4 ohms when closed.

I have a feeling these only affect the lighting and its bright/dimness when the switch is thrown or not...anything I should watch out for when adapting? Thanks!

PS: Rob, I'll need those connectors too now!

li Arc
 

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Hey Hugh!

Yes, that resistor is for the 2 different brightnesses of the backlighting. When the switch is depressed it's brighter than when it's off. This goes for the A/C, Hazzard, foglights, and Re-circ, but not the defrost. This switch only has one low brightness level as it's not a toggle switch, and it illuminates a small light inside the instrument cluster.

-Rob
 

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switches are different

The switches changed sometime around the 85/86/87 model year on c900's, I'd bet it has something to do with the 9000 being introduced. (Although I'm not sure if the early 85/86 9K's used the early switches too)...

E-z way to tell on the face of the switch is if the actual logo'd portion (with the white AC or Defrost or fog logo) is smooth or is slightly textured. The early switches were smooth on the button logo area with a textured outside portion, the later switches are all textured. My 85 SPG had smooth switches, I know by 88 they changed. But not 100% sure about 86 and 87.
 

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nashvegas said:
The switches changed sometime around the 85/86/87 model year on c900's,
Yes. The fog light switch on my 1986 c900 are the new type - the same switch on my 1984 are the old type.
 
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