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Post by crice63 on Mon Mar 27, 2017 5:02 pm

Even though I'm not ready to put the whole new dash in, I went ahead and repinned my cluster plug to prepare for the swap to round gauges. I followed the excellent description in the sticky and seemed to get most everything right. All lights and blinkers worked (that were supposed to), Water temp worked when I switched to the sender. Voltage did not work. Fuel I couldn't tell--it went to full, but the tank is indeed full; it did not go down when I turned off the power, so I'm not sure what that means. The key item is that on the test drive I got about 10 blocks out and 5 blocks back when the car died. It did not sputter like out of gas or fuel pump but died hard like no spark, and would not start, even though it was turning over. I pulled the cluster and it started no problem. Tonight I hope to sit down with the cluster again and see if I can trace which pin I have misplaced.

I know I have all the positive pins in place to the lights and gauges, those are easy to see. It is the other pins, that carry power or ground to and from the items. I will post my chart or some pics to help future swappers. I had two blacks--grounds--in my old cluster but only one is recorded for the round cluster, so I had a black left over. In my electrical chart for the 75's it shows those two wires joined and then grounded, so I was assuming that having only one connected would be OK. We will see. This wiring in the car has been reworked in many places, so this might be more of a challenge than working with straight stock wiring.

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Post by crice63 on Tue Mar 28, 2017 1:03 pm

Last night I switched the two black wires (grounds)--one had been not connected and the other connected. The volt gauge worked (though it registered something slightly different every time it was turned on--between 14 and 12.5), the water temp worked with ignition on and headlights on or off, but spiked with ignition off/headlights on. All lights worked as expected. So it looks like I need to ground that other black wire somehow, even though there are no additional "ground" slots available on the circuit board. Fuel still registers Full, so I don't know the issue there. My fuel and temp gauges are from the 73, so I wonder of the resistance pattern for the 73 sender might have been different from the 75 sender?

Electrical is bewildering.

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Post by thatfnthing on Tue Mar 28, 2017 1:30 pm

crice63 wrote:Last night I switched the two black wires (grounds)--one had been not connected and the other connected. The volt gauge worked (though it registered something slightly different every time it was turned on--between 14 and 12.5), the water temp worked with ignition on and headlights on or off, but spiked with ignition off/headlights on. All lights worked as expected. So it looks like I need to ground that other black wire somehow, even though there are no additional "ground" slots available on the circuit board. Fuel still registers Full, so I don't know the issue there. My fuel and temp gauges are from the 73, so I wonder of the resistance pattern for the 73 sender might have been different from the 75 sender?

Electrical is bewildering.

Variance in the voltmeter is not unexpected -- the stock alternator has a 'sensing' wire to it which it uses to see what the electrical demand is currently (no pun intended), then changes the output accordingly. Nothing to worry about until the voltage drops consistently below 12V.

Where does the 'other' black wire go? Typically in a GM harness any black wire is a ground, but I am always loathe to ground something without knowing for sure where it comes from. If it is indeed a ground wire, just about any connection to metal on the body/chassis will do.



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Post by crice63 on Tue Mar 28, 2017 1:51 pm

So I guess the problem about the ground wires is this: My sweep cluster had two ground "slots"--two positions on the circuit board that mapped onto two black wires at different positions in the connector. According to the book, those wires are joined together, then grounded somewhere.

When I trace the new cluster, and also according to the map laid out in the sticky, there is only one slot for a ground. One would think that as long as that slot has a black wire in it, all the necessary grounds in the cluster would be grounded, and everybody would be happy, but it's not working that way. So I'm not sure what the problem is. Maybe I should try to find that ground and verify that it is actually connected? Which would raise the question--does anyone know where the main dash harness ground is?

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Post by thatfnthing on Tue Mar 28, 2017 3:23 pm

There are actually two 18ga BLK grounds in the stock instrument harness (circuit #150) -- one runs from the fuel gauge and one runs from everything else in the printed circuit. You should have two black wires in the instrument panel connector. Once they join the main harness, they merge with several other ground wires and appear to be bolted to sheet metal to ground. Mine doesn't have any of that anymore, so I'm working off the factory diagrams. If you can post photos, maybe I can shed more light.

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Post by crice63 on Tue Mar 28, 2017 3:34 pm

I will try to get some pics. I do have the two 18 ga black wires in my harness, but the stock round cluster does not have places for them both. On the diagram I saw that ground from the fuel gauge too, and I'm thinking that's the one that I had disconnected last night.

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Post by 73ss on Tue Mar 28, 2017 5:14 pm

crice63 wrote:Last night I switched the two black wires (grounds)--one had been not connected and the other connected. The volt gauge worked (though it registered something slightly different every time it was turned on--between 14 and 12.5), the water temp worked with ignition on and headlights on or off, but spiked with ignition off/headlights on. All lights worked as expected.

Electrical is bewildering.

Mine does the same thing, The water temp will spike full hot when the lights are on/key is off. My gauges and wiring are original to the car. Wire harness is in good shape with no butchery. I did replace the dash 20 yrs ago and always wondered if I broke a ground somewhere. Everything else works as it should, even the tach, except the key buzzer and that problem is in the column. Does anyone else have a temp gauge that does this?
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Post by crice63 on Wed Mar 29, 2017 2:01 am

Still no good pics. These are the diagrams I made. I studied the new cluster and mapped it out well, but on the old cluster, the bottom pic, I mainly was just trying to match color to function. The list on the right on the top photo is from the sticky, which is what I ended up with when I was done. 

Sweep to round gauge swap 32871024434_9e71990ff6_z

Sweep to round gauge swap 33713473445_253b1145f8_z
 
Tonight I remembered that one of the main dash grounds is at the bottom left front dash support bolt, so I cleaned it up well, but no improvement. Rather than swapping more wires I just took it around for some test rides and it seemed to go ok. The new speedo reads 5 mph high, just like my old speedo. 

I think I'm going to stay with this temporarily. When I get my tilt column reassembled I can take the whole dash out to put in the new one and revisit the wiring at that point. I will have lots of wiring to do then, including AC and radio, so I can work on it all at once.

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Post by thatfnthing on Wed Mar 29, 2017 9:39 am

When you're ready, we can go through it. It'll require some testing and poking around, but we'll get it figured out. I enjoy a good puzzle. Smile
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Post by Mcarlo77 on Wed Mar 29, 2017 12:07 pm

thatfnthing wrote:When you're ready, we can go through it.  It'll require some testing and poking around, but we'll get it figured out.  I enjoy a good puzzle. Smile

Listen to this guy! Helped me figure out an electrical problem with the Laguna.
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Post by crice63 on Fri Mar 31, 2017 1:28 pm

That is indeed a great offer. I hope the new dash will be going in sooner rather than later--I will certainly be getting help with wiring then.

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Post by crice63 on Sat Apr 15, 2017 4:21 pm

Just a brief update. I put a drop of oil in the back of the speedometer wheel, and a dab of white silicone in the top of the speedo cable, and behold, it registers exactly the right speed, according to two different free iPhone speedometers and multiple passes by one of those How Fast You Are Going temporary signs on the side of the road. So now I'm really happy with the whole deal. All the lights work (though dim--will be looking into that later), all the gauges--once I ran the car enough to use some gas I found that the gas gauge is accurate. Even better, my old square one was really twitchy, registering every bump and slosh as a quarter-tank loss or gain. This one is much more equanimous, calm.

So I still need to decide on a oil pressure gauge and a tachometer, but small steps.

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