If your car runs now I wouldn't hook it up. Previous owners may have rewired the coil for reasons like replacing points with magnetic or optical points. Insulate the wire and tuck it up out of the way.

 

Don't connect it unless you where it came from. Can you confirm that the wire comes from the solenoid? I looked at your picture at work with a bigger monitor and it appears to have traces of yellow color on the jacket. If so, then that is the +12V lead from the starter solenoid, but you need to confirm that.

 

Resistance wire is a special wire that has a resistance to electrical flow built into it. It is used to reduce the amount of power the the points operate with, enabling them to last 6K miles. It's easily identified by the fiberglass cloth jacket, needed because the wire gets warm in operation. The points are nothing but a switch, turning power on and off to the the coil, and the condenser acts like a shock absorber to electricity, it stops the electrical arcing across the points when they switch power on and off.

 

The wire in the fiberglas sheath goes down to the starter and should connect to the "R" terminal. The black wire is the "resistance" wire and goes to the ignition switch. When you crank the engine, there is a disk in the starter solenoid that connects the "R" terminal to the "S" terminal which provides a full 12 volts (or whatever the battery voltage is at that time) to the coil. This allows the coil to provide maximum output to make starting easier. Once the car fires and the starter is disengaged, the voltage is supplied to the coil via the black "resistance" wire. The resistance wire is tied to the ignition switch through a fusable link. There is 12 volts present at the ignition switch side of the wire, but due to the resistance of the wire, there is a voltage drop developed across the length of it and that is why there is a 3 to 4 volt drop by the time the wire reaches the coil. This allows the coil to run at 8 or 9 volts and helps keep its internal temperature down thus extending its life. A standard ignition coil run directly from 12 volts will run hot and not last very long.

If you are only measuring 3 or 4 volts on the yellow wire while cranking, one or two things may be the cause. First make sure you are referencing your measurement to a good ground. The case of the alternator is a good ground. If you still have a bad reading, make sure the wire is connected at the starter both visually and electrically. Set your meter to ohms and measure from the stripped end of the wire to the starter terminal. You should have less then one ohm, if not then the wire is probably broken somewhere over the run.

Good Luck!

Tom

 

Does the car start and run? It's unlikely it will start w/o the yellow 12V wire coming from the solenoid to the coil. I had a bad solenoid on my 71' and the car wouldn't start until you let go of the key since there was zero volts during cranking and the correct 8-9V in the run position.

 

The wiring harness and drawings I have on a 72 have a yellow wire to starter and the resistance wire to fuse block, no fusible link in circuit. Black wire is to the points from the negative post of coil, I be surprised if there is much difference between a 71 & 72.

 

Shown is a scan from my 71 chassis service manual. It shows a fusible link in the line going to the fuse block. I tend to agree, I don't recall seeing a fusible link in the harness so they may be referring to the resistance wire and not a link.


I'll check the Assembly manual also and see if it shows different there.

 

You all are amazing

Glenn

 

Listen to shafrs3......he knows of what he speaks.....err..uh I mean writes

Schematic is worth a thousand words




Bullshark

 

I have the same wire on my 74 (not hooked up) He said it had been hard to start, mine was also , i finally figured out it would fire right up once i let go of the switch (no power during starting) exactly where is that sylonid? My points dist. was removed and replaced with a hei dist.

 

Solenoid is on top the starter. If you have an HEI dist, then you don't need the 2 power feeds, just one 12V source.

 

So would replacing my sylonid solve my problem with no power while starting? thanks david

 

If the yellow wire from the solenoid to the coil is good, then yes, replace the solenoid.