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Another Mystery Wire

Another green wire on those years was the one going to the anti-dieseling solenoid on the carb....that would only be hot with the key on..its fused too,so if it grounded out it would blow a fuse..

You can see if the green wire in question was for the water temp sender by turning on the key,and watching the gauge as you touch that wire to a ground,it should bury the needle--only ground it for a few seconds,as too long can harm the gauge..
 
OK...New Pictures and I tested the wire...it is HOT with 12 volts when the key is on.
I traced the backup lights from the tail light forward. The wire is part of that ribbon that runs up the driver's side rail and it goes all the way to the firewall.
I traced the one wire on the passenger side rail all the way back to the top of the gas tank.

Here are more pics of the mystery wire...you can see it goes up into the harness that the wires from the starter go into.


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The only wire that I know of the is turned on while the key is on is a wire that wired parallel to the ignition system. It goes to the "R" terminal on the starter solenoid. It suppose to help provide the ignition system extra power while the motor is cranked over.
harness3.jpg

harness2.jpg
 
If my wire is suppose to go to the "R" terminal on the solenoid how is it starting right now?

What would happen if you cut that wire if everything was wired right?

This wiring is driving me crazy.

Great pics, by the way and great explanation.

Thank you.
 
All it is doing is providing assistant power to the ignition system. The key switch is still hot during cranking. Later on, it seem like gm got rid of the wire going to the "R" terminal by upping the ignition wire to ignition switch to 12 gauge.
 
It is not a good thing to have that wire exposed. I don't think it is even protected by a fuse. If it shorts or grounds out, you ignition system goes out.
 
JDNobodi said:
It is not a good thing to have that wire exposed. I don't think it is even protected by a fuse. If it shorts or grounds out, you ignition system goes out.
Click to expand...


Thanks, next step is to see if my starter is missing this wire on the "R" terminal.
 
The way it used to work, back in the bad old days, at least on Fords and I think, GM and Dodge was this.

The coil was designed to run on about 9 volts. Starters and batteries were not what they are today, and that was about the voltage you got when you were cranking.

Actually, thats not far off from today even with better stuff.

So, you had a resistor in series with the coil that was matched to the coil so that it dropped the voltage to about 9 volts.

When you fired the solenoid, it put full battery voltage on that wire which was hooked directly to the coil bypassing the resistor.

My schematic shows a wire 20Y-7B which does just that. In a 73-76 model.
 
oooo and we're coming downnnn tooooo theeee wiiiiiiiiire.....:haha:

sounds like horse racing GET IT!???

horse racing, but we are talking about wires
and we are almost done figuring out which wire it is
like when they are almost done with a horse race
they say "and we're coming down to the wire....."

it's funny, cause it's a pun see, a funny pun:waytogo:



:haha: I didn't help much, if any. I'll go back in my corner now.
 
Fordum is pretty much spot on. On GM vehicles that used a points distributor there was a yellow wire that went from the R terminal of the starter solenoid to the + terminal of the ignition coil to give a full 12 volts to the coil while the engine is cranking and once the engine starts and the solenoid is released then there will be no more voltage to that yellow wire off of the R terminal. ALL engines that run points should have no more than about 9.6 volts to the coil (unless it's a resistor coil) otherwise you will burn up the points pretty quickly. Basically there were 3 ways that voltage was reduced for point style distributors, there was either a resistor wire, an external ballast resistor, or a resistor coil.
 
I guess the question is do I need to hook that wire up or just close it and leave it off?

It has HEI ignition...doesn't have any issues starting...:dunno:
 
That wire (yellow) going from the "R" solenoid terminal to the coil on points equipped trucks is only "hot" when your holding the key to the cranking position--once you let the switch go back to "run",no power flows though it anymore--so if your getting a constant 12V with the key "on",its not that wire!...I suspect it was for the anti-deiseling solenoid,or maybe some other emission related device ,maybe an EGR solenoid or a transmission controlled spark advance switch...
 
4X4HIGH said:
Just to let you know, that water temp sender is not in the factory location and DOES NOT have the correct color wire going to it either. Factory GM water temp senders were always in the left cylinder head and had a green wire connected to it.
Click to expand...

Anybody got a picture or diagram of the Temp Sender green wire coming out of the firewall harness?
 
Those schematics I posted in the other thread show it. Look at the one showing the firewall connector.
Its the one coming out of the hole marked 35.
Wire number 20DG-35
 
You originally said this was in a ribbon running down the drivers side frame rail, right? If so, is it a 4 wire ribbon? Probably has brown, yellow, green and light green wires in it? That is the wiring for the tail lights on these trucks. It is possible that is the light green backup light wire, which should run to the neutral safety/backup light switch on the column. Obviously I am late to the party here, so if I missed someone pointing this out, I apologize.
 
CUT IT! :)

Really I have no idea what this 6 page long, 50+ post mystery wire is but when I can't figure out what something does on my truck I trace it as long as I can then eventually cut it, check to see what doesn't work now and go from there. Seems to be working out pretty good so far.
 
4X4HIGH said:
Someone has definately been in there doing something for sure as i've NEVER seen any wire loom anywhere near the fuel pump area ever.
Click to expand...

I looked at the picture you were responding to and my truck has the same wire loom running in the same place... it comes from the firewall area behind the block forward (tucked between the passenger valve cover and the intake manifold), loops down in front of the block and goes backwards by the exhaust/fuel pump. Most of them go to the starter. Eventually I need to see what they all are as they're obviously not all factory.
 
Fordum said:
Those schematics I posted in the other thread show it. Look at the one showing the firewall connector.
Its the one coming out of the hole marked 35.
Wire number 20DG-35
Click to expand...

THe "mystery" wire was solved...I am now asking about the temp sender "green" wire that was also discussed in this post.
Actually, I am looking for a photo from under the hood that shows the wire I am looking for...there a many green wires coming out of that harness...not just one or two....which "half" of the connector under the hood at the firewall does the green temp sending unit come out of.

That big square connector at the firewall under the hood has two "halfs" plugged into it.
 
Chief Brody said:
THe "mystery" wire was solved...I am now asking about the temp sender "green" wire that was also discussed in this post.
Actually, I am looking for a photo from under the hood that shows the wire I am looking for...there a many green wires coming out of that harness...not just one or two....which "half" of the connector under the hood at the firewall does the green temp sending unit come out of.

That big square connector at the firewall under the hood has two "halfs" plugged into it.
Click to expand...
Well, I again refer you to this thread, number 13.

http://coloradok5.com/forums/showthread.php?t=281817&page=2

Look at the schematic of the connectors. You will see that on the left hand side, one is labeled engine and the other, front lp.
You can also see the shape of the two connectors.
One set of wires from one plug will go to the lights and the other plug will go to the engine.

The engine one has a tab at the bottom that fits into a socket of the lamp one.
The engine one is the one with the temp sending unit wire.
Its socket 35, and it will be in the same position on the firewall that it is on that schematic.

If the picture on that thread is clear enough, you should have all you need to find that wire.

If its not clear, let me know, and I can send you the jpg via E-mail.
 
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