Check PCM/PCR fused power from battery; 15A fuse blown replace
Check 12V power to PCM/PCR
Check ground to PCM/PCR
Check 5VDC to PCM/PCR
Replace PCM/PCR if 12VDC is not present on output connector
If 12VDC and 5VDC are present at connector from PCM/PCR, replace computer box