ASCD does not set when pressed.

ASCD? You mean the cruise control?
Have you checked the brake switch?

Yes I have checked all switches and all relays and control box.

Did you actually test the brake switch and its circuits? How about the brake switch adjustment?

Have you checked for trouble codes with the gear shift indicators and are they showing correctly in dash?

I have tested the cancel switch on the brake pedal for operational functionality with circuit tester.

I do not know about 'Trouble codes with the gear shift indicators' You will have to tel me more about this.

If the transmission D indicator light does not function correctly, the cruise would not work as well.

I have checked. The only D light I have is on the selector indicator next to the shift lever and is working fine.

These are the diagnostic procedures and I believe you have to go through them once again to see where you missed out.

1. Turn ignition on. Turn cruise control main switch to ON position. If indicator light comes on, go to step 2). If indicator light does not come on, check indicator bulb and main switch. If these components are okay, perform CRUISE CONTROL RELAY test under TESTING.

2. Perform POWER SUPPLY CIRCUIT test under TESTING. If power supply
circuit is okay, perform CUT-OFF CIRCUIT test under TESTING.

3. If cut-off circuit is NOT okay, check brake cancel switch, clutch switch (M/T), inhibitor relay (A/T) and inhibitor switch (A/T). If cut-off circuit is okay, perform SET/COAST SWITCH CIRCUIT test under TESTING.

4. If SET/COAST switch circuit is okay, perform SPEED SENSOR CIRCUIT
test under TESTING. If speed sensor circuit is okay, perform ACTUATOR test under TESTING. If actuator is okay, replace cruise control module.

Can you please tell me where I find 'Testing' procedures as advised in latest answer by KHLow2008. Thanks.

Which are the ones you need? There are many and it covers 6 pages.

I would say at least the ones mentioned in your previous list of recommendations plus any others that may be of help with this problem. Thanks again.

Let me have an email so I an send them to you.

My e-mail: [email protected]

Thanks.

File has been sent to you. Hope it is helpful.

Thanks I will study it and try to effect checks. I do however notice that it states 'Maxima GXE' as well as '300ZX' My model is '300 SE' and I dont know if it is the same. Also numerous references to "Fig ..." Is there somewhere that I can view these plates/drawings?

Should be similar no matter what the model says.

I have sent a new file with the diagrams.

Thanks for information. However I have again gone through the whole system and chacked every fuse, relay, switch, actuator, Sensor, pump etc and can not find the fault. What is evident is that when I switch the car on and switch the ASCD main switch on and off one can clearly hear the relay under the hood swtched on (Activated) and off (deactivated. It seems the problem lies beyond this point in the system.

There is one item that I can not identify from the repair manual and no one can tell me what it is and what it does. It looks like a small relay but has only two connectors. There is no continuity when tested with a meter. It is connected to the sysyem with a Pink and a Red wire.Could it be faulty? see my attached photos

The schematic does not show any connectors for a Pink and Red wire. The component you have shown seems like a Diode. Did you test for continuity by reversing the polarity of the ohm meter?

If you have gone through the repair procedures, you should have come to a conclusion, I don't understand why you can't find the fault. A certain result should be be wrong or it tells you to replace the control module.

I have given up in disgust with the cruise control. You were right in your assesment that the 'unidentified' unit was a diode. it works in the door entry light system However I have another request please. Have you got a schematic drawing that shows the assemly breakdown of the air (throttle) control valve return spring assembly. Thanks (See image)

Thanks I have sorted out the assembly and car is running fine. Regards