Black/purple wire in engine harness

[TheBMan]

I'm replacing the engine harness on my '70. In the old harness and the new harness, there is a black wire with purple tracer. That wire has a push-on flat-blade connector but wasn't connected to anything. I don't see this wire in the wiring diagram. Anyone know what it's for? 

I'm not overly concerned about it because it was never connected on my car anyhow, but I'd like to know for general knowledge.

[TheBMan]

Just found this. If this diagram is correct, it looks like it's for the idle stop solenoid, which my car does not have (but would have had originally). There is a black/purple wire coming from the TCS relay on the firewall, which this diagram confirms.

I wonder why this wire doesn't show in the factory manual. 🤷‍♂️

[jft69z]

The only blk/ppl wire I see on the wiring chart is for the key warning buzzer-ground, circuit 159, and that is out of a 1972 Service manual (1970 doesn't have it).

Looks like you found the above info as I was typing 🙂 (looks like a 'Sample' diagram though, no description of what make/model)

 

72 Wire color codes.pdf

[TheBMan]

Thanks Joe! I found a couple of posts online from others who were trying to figure out what this wire was for in 1970 (Chevelle, which should be the same). I didn't find any definitive answer although one person suggested that it might be for the TCS, which I don't think is correct.

As I mentioned, it's somewhat irrelevant because it wasn't in use on my car. But it does make sense that it would be for the idle stop solenoid because originally my car would have had one.

[cny first gen 71]

If that is in fact the wire for solenoid that's the wire I used for power for my Pertronix set up instead of switching resister wire from ignition switch, was just easier and Pertronix tech said it would work fine. I removed the solenoid when I switched from 2 barrel to 4 barrel. 

[1970mcss]

It is for an idle stop solenoid. I did some research on this a while back. I never found any information that Chevrolet put a idle stop solenoid on the 454 in 1970. I have the harness to the solenoid if you need one. 

[TheBMan]

1 hour ago, 1970mcss said:

It is for an idle stop solenoid. I did some research on this a while back. I never found any information that Chevrolet put a idle stop solenoid on the 454 in 1970. I have the harness to the solenoid if you need one. 

Thanks Paul. I have the lead to the solenoid but it wasn't connected to anything because the previous owner had an Edelbrock carb on the car before I bought it. I have since put the numbers-correct Quadrajet back on the engine but I didn't bother with the solenoid because modern cars don't really need it. I didn't put one-and-one together until I figured out what the wire was for!

Crappy gasoline in the 70s caused dieseling (at times) when shutting off the engine so the solenoid was used to completely close the throttle plates. Today's gasoline is much better so cars don't "run-on" like they once did.

Side note... I'm about to put a solenoid back on and use it as a "idle-up" solenoid for my A/C. The solenoid will be off by default (opposite of when it's used as an idle stop) but when the A/C is turned on, I'll trigger the solenoid to bump the idle a bit.

[willie]

I took a look at my 72 and the wire for the idle solenoid is white. its not the original harness as i bought it from AAW. Not sure if this helps but just wanted to see what mine was.

[monte70z20]

I had posted the same question a few years back and never got a definitive answer, but it looks like the mystery is now solved!

[Scott S.]

1 hour ago, monte70z20 said:

I had posted the same question a few years back and never got a definitive answer, but it looks like the mystery is now solved!

Like dealing with the government....... It takes a while to get the answers.