From the service manual diagnostic first few steps. Checking for power and ground.
Disconnect the connector from the back of the radio (icp). Measure voltage between integrated control panel connector Pin C237-11 , Circuit 729 (R/W) and a known good ground. Hot at all times. Should be 10 volts min.
Cycle the ignition switch to RUN position. Measure voltage between integrated control panel connector Pin C237-16 , Circuit 640 (R/Y) and a known good ground. Should be 10 volts min.
Ignition switch still in RUN position. Measure voltage between integrated control panel connector Pin C237-6 , Circuit 1002 (BK/PK) and a known good ground. Should be at least 10 volts.
Make sure the ignition switch is OFF and measure resistance between integrated control panel connector Pin C237-8 , Circuit 57 (BK) and a known good ground. Resistance should check 5 ohms or less.
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