Engine wiring harness swap

2003 CHEVROLET SILVERADO

100,986 MILES • 5.3L • V8 • 2WD • AUTOMATIC

LOUIS W NAGY

MEMBER
55 POSTS

Hello sir, out of desperation I picked up an engine harness off of EBAY. it was out of a 2006 but was suppose to be the same as 2003 but when I looked at it I discovered it has the newer charging system on it ,it has the module attached to battery cables to monitor voltage ,and from what I have read I’m not sure if it’s going through ECM. I have not compared the harnesses side by side yet. so, do you know if it will swap with just some minor work are no? I’m out $200.00 if not. it's one of those you buy it no returns. Thanks for any input.

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Oct 16, 2020 at 1:03 PM

KASEKENNY

✓Experienced Mechanic
18,907 POSTS

Yeah. Looks like that is the generator battery control module. Assuming the connectors are the same then you may be able to just eliminate this module. Your vehicle does not have it so the PCM will not know how to use it so you need to rewire this harness to match how your vehicle is equipped. However this can be done but take for example the supplemental brake assist pump. On your vehicle this is run off the alternator. On the new harness that you have, it is run from the module. So you will need to take that wire from the module and run it it the alternator.

If you have the original harness you may need to replace the alternator connector so that you can run the wire to it. I would just cut it about 5 inches behind the connector and then solder your wires in place.

Does this make sense? Let me know what questions you have. Thanks

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Oct 17, 2020 at 12:51 AM