The "quick test" is in bold below for readers who wish a shorter piece. I read the manual "see below" and found a faster test that performed better for me than what the manual recommended for the Automatic Speed Control Device (A.S.C.D.) aka the cruise control.

Background - We have had a 1993 J30 for many years and the cruise control never worked. The light on the dash button would come on; however, there was never any indication that the cruise control would engage.

Yesterday, I decided to work on it again and got it working. The quick test I did followed other posts suggesting the brake light switch is a common problem. My brake lights always worked properly, so it did not seem to be the issue; however, as I explored further there are two side-by- side switches near the brake pedal arm activated by the brake pedal (i.e., the brake light switch toward the passenger side of the two and the BROWN cut-off switch on the driver's side door of the two).

The brown one was the culprit and it seems to be called the ASCD inhibitor switch in the manual. When the brake pedal is at rest (i.e., not depressed) this brown switch is normally closed (i.e., it allows current to flow through the switch to complete the circuit). The brown switch opens and does not allow current to flow when the brake pedal is depressed. The opposite is true for the brake light circuit, of course.

Disconnecting the two wires going to the brown switch was easy; just depress the blue strip that goes across the connector and the wire connector is easily removed.

Next, I pulled the two wires and connector down a bit for easier access. Then took a wire and inserted it into each side of the connector creating a jumper wire (a paper clip would work as well provided it does not touch any other metal).

I made sure the dash button for cruise illuminated, then I drove the car because it must be going at least 30 MPH for the cruise control to work. Then once over 30 MPH I pushed the set button on the steering wheel and a green light saying something like "cruise control" came on the instrument panel (I had never seen this since the cruise never worked) AND the cruise control worked! I then knew this quick test verified the brown switch was faulty.

To my surprise, when I touched the brake the cruise control disengaged. I tried it again with the jumper wire connected and when I removed the jumper wire, the cruise control disengaged. It seems like Infiniti created a backup system to ensure the cruise would disengage if the brake is depressed.

The brown switch is easy to remove with a 14mm (maybe it was 13mm??) open end wrench to slightly loosen the nut; then unscrew the switch. I shook the switch and heard it rattle; later, I took it apart to see it had broken internally. If you take it apart, it should have two copper pieces inserted into the plastic, a plunder, and a spring. Seeing it, I realized it should not rattle at all. I knew I would almost certainly have to buy a new switch for $20 to $60 depending on the source. I had some extra time so I tried reattaching the copper piece that literally broke off with solder. Although I had little expectation it would work, it held; I even had to bend it afterwards to ensure the contacts would touch. Do not expect to be so lucky.

By the way, I read the Service Manual, which is incredibly handy in its driver's side trunk compartment (Thanks Infiniti!), about the Diagnostic procedures for the Automatic Speed Control Device (A.S.C.D.) aka the cruise control. I went to Page EL94 because it seemed like Diagnostic Procedure 1 was the best (See Page EL92 for the chart). I could not seem to get the tests to work on the bottom of EL-102 and this is why I tried my quick test. I followed the directions carefully, even having it in drive with the key on.

I hope this helps others. I wish I had tried it first before replacing other parts.

Thanks for posting this! I had the exact same thing with the Q, my brake lights worked fine but the cruise control would randomly stop working, then not work at all.. I actually had a spare switch, swapped it in and it worked...

I have a unique issue with my cruise control. I have bypassed the brake switch with the jumper as mentioned. My dash button works (lights up), and when attempting to set cruise using the steering wheel switch, the Cruise light in the cluster blinks. It does not hold speed. I have to use the button on the dash to turn off the blinking cruise cluster light. Hitting the brake pedal or using the steering wheel to try to cancel does NOT turn of the blinking cluster light. I uploaded a quick 17 second video documenting my problem:

http://youtu.be/NQ5eEHPdt38

I have replaced the steering wheel switch along with the ASCD module to no avail. I also swapped the relay under the hood with my heated mirror one (same relay) and also did not have any effect. I have also verifed my actuator works, by applying 12v directly to it and can hear it.

Well guys, any suggestions?

Got my cruise working as well. Turns out I had left the actuator connector unplugged after testing. I connected the 4-pin actuator connector (under the hood) and now my cruise control is fully functional! Im going to order two new rubber stoppers and a new ASCD cancel switch as well.

silly humans!
good work retracing your steps.....

Hey guys!

I just picked a '95 J30t for winter. I'm a big-time lover of Z31's, but I have to admit, beginning to fall in love with this heavy four-door. However, do you guys have a part number for the Automatic Speed Control Device Inhibitor? Can you also suggest a place to purchase this? Is there a known dealership website you guys buy the majority of these smaller odd parts? Z31 guys use courtesy parts.com (because our cars are so old, some parts are NLA via RockAuto/Napa/etc).

Thanks for this information! Excellent write-up, as this is indeed the issue my car is plauged with.