A/C wiring, where is the ground?

[Roger Zimmermann]

A friend of mine has trouble with his 1959 electrical installation. The fast idle solenoid was replaced with an incorrect device. Anyway, in order to help him, I was looking at the A/C electrical schematic. The attached image is from the '57 shop manual; the '59 one has a more complex wiring but the function is the same.
My problem:

When the A/C is on, the current is coming from the 25 amp fuse to the compressor switch; when the switch is closed, the current is going with the black wire to the compressor clutch solenoid and then to the ground, closing the circuit.
There is a junction at the black wire: another black wire is going to the fast idle solenoid, then to a violet wire going to the "sol" contact of the ignition switch. Another wire is going also to the neutral switch (closed only in P and N, disconnecting the fast idle solenoid when the gear lever is out of P or N. Here is my problem: where is the ground to activate that solenoid?

[wbdeford]

page 14-8 of 1959 shop manual:

'Current for the fast idle solenoid is furnished from the Air Conditioner "On-Off" switch with the ground being completed through the neutral safety switch.'

[Roger Zimmermann]

Yes, I can read that too, but, by looking at the schematic either on the page 14-7 or at the page 12-47/48 I see a ground at the neutral switch....Further, if there is a ground at the neutral switch, how can the current be sent to the starter solenoid?

[J. Gomez]

Rogers,

Oh yes, that pesky elusive ground source for the idle speed-up solenoid..! 

Since Cadillac engineers keep the same tradition as previous years with the idle speedup solenoid operation, the ground for it comes from the starter solenoid hold-down coil.

The idle-speed up solenoid is only operational while the car is in “P” or “N” as the ground is feed via the NSS. Same method as it was on previous years.

The attached diagram shows the 12DBL (12gauge Dark Blue wire) goes from the NSS over to the starter solenoid.

Good luck..!

[Roger Zimmermann]

And there was light! Thanks Jose for the explanation. By looking at the starting circuit, it's so clear...