Idle Stop Solenoid

[roadking77]

Still trying to get my motor wire up.

The carb I have is a correct numbers for a 79 4 speed q jet. It did not come with my car, I tracked it down. It does have an Idle Stop Solenoid.

I have a couple of questions.
A.- I have an extra green wire on the harness that ends at the alternator connection. In that end of the harness there is the plug in connector for the alt. the red wire that attaches to the bolt on the alt., the green temp sender wire and another green wire with a plug. Does this extra green wire go to the Idle stop?

B.- Looking in the Ames catalog, they have a new part (Idle Stop S.) with the years through 1979 BUT there is a note that says
"except trans am". I have not called Ames yet for an explanation, thought maybe someone here may know if this part was supposed to be on a trans am or not.

On a side note I looked at the motor (400 auto) in my 77 and there is NO ISS.

[b_hill_86]

A. From memory, yes I believe the ISS wire is green and would terminate over on the alt side. I’ll dig up a diagram and double check.

B. If you’re asking if a trans am would/could be equipped with an ISS, yes. My understanding is for at least the years around 77-79 (I only choose those because that’s what I’m most familiar with) would have one equipped on AC only cars. Does your 77 have factory AC?

Seems to me the earlier 2nd gens used them as the name suggests. They were wired to 12v ignition power to open the throttle blades slightly at normal idle and close them when the key was shut off to prevent dieseling or run-on. In the later configuration they’re wired into the same circuit as the AC compressor to raise idle with the AC on. Someone correct me if I have anything wrong or backwards.

[b_hill_86]

The 79 manual supplement interestingly notes a change to a dual purpose low pressure/temp switch but doesn’t provide a different wiring diagram from 78. That 78 diagram shows the wire to the solenoid being light blue. I’m pretty sure my 77 is light green. Anyway it also interestingly says “for L80 only” but I have a hard time thinking 403s would have only gotten them in 78. I’ll have to dig further.

[5th T/A]

Still trying to get my motor wire up.

The carb I have is a correct numbers for a 79 4 speed q jet. It did not come with my car, I tracked it down. It does have an Idle Stop Solenoid.

I have a couple of questions.
A.- I have an extra green wire on the harness that ends at the alternator connection. In that end of the harness there is the plug in connector for the alt. the red wire that attaches to the bolt on the alt., the green temp sender wire and another green wire with a plug. Does this extra green wire go to the Idle stop?

B.- Looking in the Ames catalog, they have a new part (Idle Stop S.) with the years through 1979 BUT there is a note that says
"except trans am". I have not called Ames yet for an explanation, thought maybe someone here may know if this part was supposed to be on a trans am or not.

On a side note I looked at the motor (400 auto) in my 77 and there is NO ISS.

I agree with what Brian has said. I don't know for sure but believe in 1979 the idle stop solenoid engaged when the AC compressor clutch is energized.

Here is a wiring diagram for a 1980 TA. The diagram is from an aftermarket company, so you can't 100% trust it. But, before I did the engine upgrade on my 1980, the solenoid would only engage when the AC compressor clutch was engaged.

IMG_2632 by Lawrence Alexander, on Flickr

Here is a picture of my 301 showing a light green wire attached to the solenoid. Once you have all the wiring in and a battery connected you can verify the purpose of the unknown wire. With the ignition turned on, switch the climate control selector to AC mode and you should see 12 volts on the wire.

IMG_2631 by Lawrence Alexander, on Flickr

[b_hill_86]

He will only see 12v though if there is pressure in the system. If the low pressure switch doesn’t detect pressure it doesn’t close the circuit that feeds power to the compressor and solenoid

[5th T/A]

As I said before, my car is a 1980 and the drawing is not a genuine GM schematic. But if you go by the drawing, the state of the pressure switch only affects the compressor clutch, not the idle stop solenoid. The power feeding the pressure switch and idle stop solenoid are the same.

But if the idle stop solenoid power does come through the pressure switch, all you would need to do is put a jumper in place of the pressure switch.

[b_hill_86]

Duh, I hadn’t thought about a jumper. That would work. Anyway, here’s a 78 diagram. There is no 79 diagram to my knowledge since 79 just received a supplement.

[roadking77]

Thanks, that all makes a bit of sense.

Yes my 77 has air con. but the car had been mucked with over the years and I am sure things have been changed a good bit. When the motor was rebuilt he put things back in the car in a good running condition. He is a great mechanic but not a stickler for detailing. I am sure the school of thought was that if it was not there no need to install one. There is the green wire though and it goes into the harness for the air conditioner.

With the new harness for the 79 I can see how it will plug right into the solenoid.