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Old 11-02-2018, 11:28 AM   #1
kcmarkd
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Temp Gauge Wiring @ Ignition Switch

Hello All,

I have read and read a ton of the various posts regarding the temp gauges, and while all great info, learned a lot, I have a different question that I hope someone can give me a pointer or two.

My project is a 1970 C10 LWB CST, mostly stock with the exception of a different engine. Factory put in a 350, but one of the POs replaced the 350 with a '66 283. The truck has gauges for temp and such, not warning lights. Couple of notes, then my question:

- I did not have a temp sender. I have since located and installed one.
- I did locate the dark green wire under the hood. But, mysteriously it was connected to the + side of the coil. No clue why.
- I have traced this dark green wire to the correct pin on the engine side of the firewall.
- I see a dark green wire connected to the correct pin in the back of the instrument cluster.
- My intent was to do some continuity checks to verify the wiring, but found that the two dark green wires that are supposed to be connected to one of the spades on the ignition switch are nowhere to be found.

My question: short of gutting the entire dash wiring harness, can someone tell give me a pointer on where these two dark green wires were originally routed? Did they join the rest of the wire bundle that is routed behind the cluster?

While my ultimate plan is to replace all of the rats nest of wires, I did not want to have to do that now.

Thanks in advance.
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Old 11-02-2018, 11:34 AM   #2
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Re: Temp Gauge Wiring @ Ignition Switch

http://outintheshop.com/faq/wiring/w...s/image002.jpg

http://outintheshop.com/faq/wiring/w...s/image003.jpg
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Old 11-02-2018, 11:37 AM   #3
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Re: Temp Gauge Wiring @ Ignition Switch

Notice in the second image, there are 2 pinouts for the dummy light cluster and the gauge cluster.

It runs through the ignition switch to test the dummy light while cranking. Not sure if it does that with the gauge.
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Old 11-02-2018, 12:00 PM   #4
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Re: Temp Gauge Wiring @ Ignition Switch

rpmerf, thanks for this. I have found these earlier this week, printed them, squinted at them, and seeing what wires are supposed to be there. My challenge is that I am seeing no evidence of these two dark green wires anywhere near the ignition switch. Been spending time laying on my back with a flashlight searching under the dash for where they might have been routed. I might have to surgically dig into the bundle right behind the gauge cluster.
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Old 11-02-2018, 01:18 PM   #5
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Re: Temp Gauge Wiring @ Ignition Switch

rpmerf, well I just re-read your posts and didn't pick up on what you were alluding to. If the purpose of the two wires going to the ignition switch is to test is during starting, it would make sense to me that I would not have those since I have a gauge. I do have the two 20T wires that go to the brake warning light/sensor, so those should test during cranking.

So, my next step is to do continuity tests using the existing wiring and see what happens.
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Old 11-02-2018, 07:09 PM   #6
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Re: Temp Gauge Wiring @ Ignition Switch

You did catch on to what rpmerf was saying.

I think a truck with a gauge cluster just has the green wire entering the cab and going to the cluster to run the temperature gauge. The ignition switch is not involved. I just looked at the back of the ignition switch on my truck and I don't have the dark green wires going to it.

I think when they made the wiring diagram, they concentrated on the cab wiring for the warning light cluster, and only as a sort of afterthought added a pinout for the gauge cluster. They don't give us info about how the cab harness would also have some differences. You may also notice that the ammeter wires are on the engine side of the diagram but completely missing from the cab diagram, because the cab is presumed to have a warning light cluster.

So, check for continuity between the dark green wire on the cluster connector and the end of the dark green wire that you intend to connect to the temperature sender. Check that your cluster plug has the colors of the wires oriented as in the gauge cluster pinout as seen in the diagram. Then hook up your temperature sensor and see if it works.
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Old 11-03-2018, 03:31 PM   #7
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Re: Temp Gauge Wiring @ Ignition Switch

Hope this helps,

At the cluster connector #6 location, dk green wire, ohm from there to where it hooks to the sending unit on the engine. It is basially a straight shot through the harness. If it is open, then a repair or replacement of the wire is needed.

The only cluster feed from the ign is for power at the pink wire at #3 location on the cluster connector. This supplies voltage to the temp gauge as well as the fuel gauge and the power splits in the circuit board.

The wire should follow through the harness to the bulk head and then to the engine compartment. If you have key on and ground the green wire briefly, the temp gauge should peg.


Tom
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Old 11-03-2018, 09:14 PM   #8
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Re: Temp Gauge Wiring @ Ignition Switch

Guys, thanks for the tips and suggestions. They are on my list to dig into tomorrow. Today was spent with replacing points, condenser, cap, rotor, setting dwell and timing, then some minor carb adjustments.

During that process, I might have discovered another contributing problem. Well, seems that I ran out of gas during the tune-up process. Fuel gauge showed 3/8 of a tank, but it was empty. Hmm, so fuel gauge not working too.

Next up will be to verify power on the pink wire to #3, then test continuity on the temp sender wire.
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Old 11-04-2018, 07:06 PM   #9
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Thumbs up Re: Temp Gauge Wiring @ Ignition Switch

Wanted to close the loop on this post.

Late last night I went back to basics. Started with power. My old eyes could not see that little tiny wire in the 3A fuse, so I removed it to inspect under better light. Naturally the fuse shattered. I love glass fuses, said no one ever.

This morning, after the run to get more fuses, I verified good power on the pink wire to the cluster connection. Verified good continuity on the temp sender wire (dark green) from the cluster connection to the other end under the hood. I used a test lead to complete the connection from the sensor wire under the hood to the post of the sensor, then let the engine warm up, and lo and behold, the gauge moved. Kept it running and verified that the entire circuit seems to be working just fine.

Finally, I extended the existing wire from where it had been cut near the firewall, soldered, heat shrinked, wrapped it in heat resistant tape, routed it on top of the engine, then connected it to the sensor.

Thanks to you guys for the help and guidance!
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