All the controls on the steering wheel on my 1988 nissan 300zx stopped working all of a sudden (radio controls and cruise control). How do I fix it?

It depends on what's wrong with it . Does your vehicle have any other buttons on the steering wheel ? cruise control , radio control etc... Is the air bag light lit on the instrument cluster ? A common part that fails in all make an model vehicles is the clock spring . It's located under the steering wheel on top of the steering column . If any other buttons on the steering wheel aren't working an the air bag light is lit more then likely the clock spring is bad .Watch this video . https://www.youtube.com/watch?v=UMbGhxdXrUc
If not this could be the horn relay , https://www.youtube.com/watch?v=WDn4ZKJsdpY

Testing electrical circuits are required to find the problem .

This is usually the sign of a bad clockspring, The steering wheel controls go through the body control module.

Steering wheel radio controls and horn not working - Jeep Wrangler ...

www.wranglerforum.com/.../steering-wheel-radio-controls-and-horn-not...

Sep 22, 2014 - 12 posts - ‎6 authors
... 2Dr sport and my step/reset buttons, radio control and horn all stopped working. ... Also the lights behind the step/reset and cruise control went out, but the ... Soundslike a bad clock spring ribbon cable in the steering wheel. steering wheel buttons not working
30 posts
Jun 14, 2012
Steering wheel audio controls
30 posts
Mar 5, 2011
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seems like you need to replace the sir clock sprin

there is what is called a clock switch located under the steering wheel that must have went kaput. it is what transfers the signal to the steering column.

hi
long story short, your car problem is, the spiral cable is braking up.
it fits under the steering wheel,
spiral cable is the part that connect the moving side (steering wheel)function buttons, horn, air bag, to the fixed side (car electric loom).
good luck

Maybe. Sounds like you have a connector loose or broken wires in the column, OR a blown fuse that supplies it all.

Ther is a control unit in the dash that fails intrmittantly, replacing this control unit will most likely fix it.

check brake switch under dash above the brake pedal. See if sensing wires are broken . or if it uses a duplicate switch sensor check it is engaging properly. Also check you tube on possible failures.
Also in the engine bay the cable from the accelerator petal will attach to the trottle on the engine. Check for another cable at this location from the cruise control and check the cable is not broken .

Check brake globes are functioning and are not blown as well.

The problem is the coiled ribbon contact under the steering wheel (we call it the clock-spring contact) that connects the stereing wheel controls to the steering column wiring harness, this is a printed circuit that is coiled to allow the wheel to move and still have a psychical contact for the wheel switch's and the airbag, anyway replace that contact coil, u must disarm the airbag to do this repair, follow the factory procedure to do this or serious injury can result if the airbag fires.