Hi guys I have a 4l80e swap unsure of what year but the internal wiring harness is leaking through the pins and I want to replace it but I'm unsure of how to determine what year my trans is... are all 4l80e internal wiring harnesses compatible?

 

I think there's just 2 breaks on wiring harnesses for the entire production of the 4L80e. I've used this on the 2 rebuilds I have done, both were 1995 model units. Rostra (24222798 (350-0032) / 24241218) Wire Harness, 4L80E Internal (Male) W/Temp Sensor (1991-2003) https://a.co/d/289FF5V

Your transmission doesn't have a tag? Does it have the 12 o'clock LS bellhousing bolt hole on the bellhousing?

 

found this awhile back.
But your valve body should have a Date stamp on it as well

 

There are 3 harness variations for the 4l80e

91-93
94-02
03+

91-93 is the first gen and should just be replaced with the 94-02 version. The 91-93 is a different plug and it leaks and has a non vented epc.

04-03+ are all the same other than the epc connector. 03 swapped from a flat spade type connector to a 2 pin plug on the epc.

The external harness portion is the same plug and you can swap them all no problem. EPC internally just needs to match the plug on the harness.

 

I have old style on a '92. External wires are old and exposed wires..Can I replace the external harness with the new style only, or do I also need to replace the internal harness?

 

If it looks like this yes you will have to replace the transmision harness. In the middle of this literally as we speak and need to get it finished by Wednesday along with a rebuild/reinstall.