I am putting a 5.3 in a S10 Blazer. Well went to test some things on the harness and I found that there was power on terminals 4 & 5 on the diagnostic connector. My understanding is that should always be ground. I don't understand how it could ever have power on it unless there is a dead short somewhere. Can someone put some light on this subject?

Info on the truck:

Motor is an 02 Tahoe 5.3
Harness is aftermarket standalone. Computer matches the motor.
The only thing that might be wrong is when the harness was ordered it said 99-01 LS1 on the instructions I got in the box. Would that make something weird happen like this?

I always thought if something is grounded it should go straight to ground not have the ability to be power or ground.

 

pin 2 is purple - serial data line
pin 4 is black - ground
pin 5 is blk/wht - ground
pin 16 is orange - +12VDC constant power with switch off.


This is fairly universal, expecially with GM ECMs

The pin numbers are at the OBDII top left to right

There should only be 1 +24VDC

I bet pin 4 or 5 was terminated at the wrong location.
Put a meter on 4 and 5 and just reroute the end of that wire to ground.