Yet Another Starter Wiring Question

[Gregski]

guys please help, I searched for wiring diagrams and found the link but I can not read those things to save my life, I am sorry

my question is simple I have a stock '74 GMC with points ignition and it is starting / running fine but there is one yellow wire by the starter that is loose and it is bugging me I don't know where it goes cause it does not have a loop connection on it so I can't tell which stud to put it on. The other wires are

big fat black wire is connected

orange wire and red wire are already connected to the same stud

purple wire is already connected to another stud

[Sodak]

Do you know where it ends up?

[Gregski]

Originally Posted by Sodak

Do you know where it ends up?

I do not, it runs up to the engine but its wedged so tight with the other wires that I can't easily yank on it

[Bigstevex4]

This guess but hooks to solenoid so when cranking it supplies full voltage to points.

[Gregski]

as interesting as the Service Manual is with all their Theories of Operation sections I have yet to find an answer to any of my questions in it, this is their picture of the starter solenoid

[Gregski]

Originally Posted by Bigstevex4

This guess but hooks to solenoid so when cranking it supplies full voltage to points.

I think so too, but there are like 3 or four studs on that thing so which one does it go to?

[Dead Parrot]

Attached is a pic from a 1963 'Fix Your Chevrolet' book an old style shade tree mechanic gave me when I was a teenager. No color code is given but it might help with the solenoid terminals.

[hatzie]

According to the 1974 GM wiring diagrams:

• The 2 gauge Black Battery + cable and the Orange & Red Fusible links go to 3/8" "B" Battery stud.
• The Purple Start wire from the ignition switch start position goes to the #8 machine screw "S" stud (Solenoid winding terminal in your pic).
• The Yellow wire is supposed to go to the #10 machine screw "R" stud ("Ignition coil" stud in your pic) to provide power to the coil when the starter is engaged. Not sure why she starts.

There's a lot of detail in the wiring diagrams if you know what you're looking at.
The wires are labeled {(American Wire Gauge) Color - (Circuit Number)} The Yellow wire is labeled 20 Y - 7B {(20AWG) Yellow - (Circuit 7B)} Note the "NO. 10" next to the ring terminal graphic. It means #10 machine screw stud size.

[Gregski]

Originally Posted by Dead Parrot

Attached is a pic from a 1963 'Fix Your Chevrolet' book an old style shade tree mechanic gave me when I was a teenager. No color code is given but it might help with the solenoid terminals.

Thank you, this was helpful but still a bit too generic. I do appreciate it though.

[Gregski]

Originally Posted by hatzie

• The Yellow wire is supposed to go to the #10 machine screw "R" stud ("Ignition coil" stud in your pic) to provide power to the coil when the starter is engaged.

Thank you very much you really went above and beyond, I so appreciate it as well as all those who come across this thread in the future.

Originally Posted by hatzie

Not sure why she starts.

I know right? This is the reason why I posted this question, if that yellow wire is so important why does my truck start and run without it.

I think it is time to strip the electric tape off of that wire bundle and follow it up to see where it goes (as there is no yellow wire at the coil) it will be a fun learning experiment.

Again very much appreciate you taking the time to teach me/us.

[hatzie]

The 1974 wiring diagrams show circuit 7B splices (Splice 3-7) to circuit 7A (coil + wire) near the coil. It also shows a P/B (Purple with Black tracer stripe) resistance wire hooking onto that same splice. GM didn't use a ballast resistor. P/B, Circuit 3, runs back to the firewall plug. The Ohmages for that resistance wire are listed just under the splice. V8 & I6 are different Ω.

Before you rip open the harness cover... Strip the yellow wire jacket back at the starter end (you'll need to do this anyway to crimp on a new #10 ring terminal) and check continuity up to the yellow wire at the coil + terminal... Use a meter set to read Ωs or better yet the continuity buzzer.

PDFs of the GM wiring diagrams for individual years, not just a one size fits all diagram, are in the RTFM link in my signature. BTW 1974 seems to be able to stand 600% magnification in Acrobat Reader.

[lilpoindexter]

I thought i had a wire that I forgot to connect on my straight 6 '78. Someone on this forum pointed out that it was a unused wire in the loom for an oil pressure gauge, which my truck doesn't have.

[Gregski]

Originally Posted by hatzie

The 1974 wiring diagrams show circuit 7B splices (Splice 3-7) to circuit 7A (coil + wire) near the coil. It also shows a P/B (Purple with Black tracer stripe) resistance wire hooking onto that same splice. GM didn't use a ballast resistor. P/B, Circuit 3, runs back to the firewall plug. The Ohmages for that resistance wire are listed just under the splice. V8 & I6 are different Ω.

Whacha say Woody?

[Gregski]

Originally Posted by hatzie

Before you rip open the harness cover... Strip the yellow wire jacket back at the starter end (you'll need to do this anyway to crimp on a new #10 ring terminal) and check continuity up to the yellow wire at the coil + terminal... Use a meter set to read Ωs or better yet the continuity buzzer.

Now why didn't I think of that, great advice, I will try it tomorrow, thanks again, very much appreciate all the advice.

[hatzie]

Originally Posted by Gregski

Whacha say Woody?

Follow the yellow wire on the GM wiring diagrams. You'll see the splice I was commenting on.
The rest will make sense when you look at that section of the diagram.