Code p1593 speed control sensor

Code P1593 isn't a sensor it refers to the speed control switch on the steering wheel. However it could be a bad switch, bad clock-spring, bad harness or bad control module. To test you have to remove the air bag module from the steering wheel then remove the steering wheel, then the clock-spring and finally unplug the switch, then use a scan tool and test to see if the correct voltages are present on the wiring coming through the plug. Without a factory scan tool you would be very limited to testing and likely would only be able to change out the switch and hope it was the problem.

How do i order for 1978 chevy caprice th350 with cruise control.

HAVAS BORES Could you please use this link and ask this as a new question, please specify what it is you are trying to find as well, thank you.
https://www.2carpros.com/questions/new