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Old 01-24-2020, 12:51 AM   #1
2120
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Cluster swap question

Currently in the process of swapping out my 77c10 with gauges over to a 78 tach cluster. When re-pinning my brake ground in pin #6 over to #17 there’s already a tan wire in the # 17 pin location. Also the #6 pin has 2 tan wires going into it.
My question in is do I combine #6 to #17 and have a total of 3 tan wires in that spot? Or do I just leave the #6 tan wires out altogether?

Thanks for the help in advance.

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Old 01-24-2020, 12:20 PM   #2
MJN
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Re: Cluster swap question

Why are you re-pinning your connector, was the truck originally only warning lights and no gauges? If you had gauges then the tach cluster will be a direct swap, no need to re-pin. I installed a factory tach dash in my '74 and didn't have to repin the connector.
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Old 01-24-2020, 02:01 PM   #3
2120
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Re: Cluster swap question

The truck is a 77 with gauges and the cluster is from a 78. They have different pin locations. I think 78-87 are all interchangeable without having to repin.
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Old 01-24-2020, 06:02 PM   #4
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Re: Cluster swap question

78 changed to electric oil gauge. If you are using a 78 cluster in a 77 truck, you will have to run a wire from the sender and wire per the 78 schematic for this to work.

That is the big change on the cluster between 77 and 78.

I see just from looking at the chart, there are some other differences. Turn indicators for example, in a different location on a 78.

Hope this helps,
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Old 01-25-2020, 05:00 PM   #5
ray_mcavoy
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Re: Cluster swap question

Quote:
Originally Posted by 2120 View Post
Currently in the process of swapping out my 77c10 with gauges over to a 78 tach cluster. When re-pinning my brake ground in pin #6 over to #17 there’s already a tan wire in the # 17 pin location. Also the #6 pin has 2 tan wires going into it.
My question in is do I combine #6 to #17 and have a total of 3 tan wires in that spot? Or do I just leave the #6 tan wires out altogether?
The 77 gauge clusters had two different locations for the "brake" warning light depending on the cluster. The regular (RPO Z53) gauge clusters had the brake light located in the lower/left corner and it was connected to pin #6. The clock (RPO U35) and tach (RPO U16) options make use of that lower/left opening for the clock, or to re-locate the fuel gauge. So they re-locate the brake warning light to a window at the bottom of the fuel gauge or tach faceplate where it is hooked up to pin #17. To make the wiring compatible with the different cluster styles, the 77 wiring has the tan/white (circuit #33) brake warning light wire running to pin #6 and a then second branch running from pin #6 over to #17. That's why you are seeing 2 wires on #6.

The 78 (and later) gauge clusters all have the brake warning light in a window at the bottom of the fuel gauge (or tach). The lower/left opening is no longer used for the brake warning light. So these clusters all use the pin #17 connection.

So you can leave the pin #17 connection as-is. But the 78+ gauge clusters make use of pin #6 as a +12V feed so you can't leave that one as-is.

I'd recommend extracting pin #6 from the connector (leaving the wires attached) and insulating the terminal with some heat shrink tubing. That will keep the brake warning light circuit to pin #17 intact and it will free up the #6 cavity to accept the +12V feed wire.
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