Allison 1000 Internal Transmission Wire Harness 29543336

This is the internal wire harness that lives inside the Allison LCT 1000, 2000 and 2400 transmission and ties the seven shift and pressure control solenoids to the 20-pin case connector. It replaces GM 29543336 and crosses to Rostra 350-0087, Transtar 121446C, GFX 411511BDR, Natpro 35869D and WIT 116446B. It is the Gen 4 seven-solenoid layout used on 2006-2009 Chevrolet and GMC 6.6L Duramax trucks (LBZ and LMM), so confirm your unit is the six-speed before ordering.

When this harness goes bad the truck does not usually die outright, it starts throwing solenoid codes. P0776, P0778, P0842, P0843, P0973 and limp mode that clears after a key cycle are the usual complaints, and they move around because the fault is a chafed or heat-hardened wire, not a dead solenoid. Hot ATF cooks the insulation over time and the harness rubs where it passes the main case rib. A lot of Allisons get a full solenoid set thrown at them when the harness is what actually failed, so ohm the harness out at the case connector before you spend the money on solenoids.

Replacement is a pan-down job on the bench or under the truck. Drop the pan and filter, unplug the seven solenoid connectors and the pressure switch, release the case connector retaining clip and push the connector up out of the case, then unclip the harness from its routing tabs. Feed the new harness in the same path, seat the case connector until the clip snaps, plug the solenoids back in by their keyed connectors, and re-check that nothing sits against the pan rail before the pan goes back up. Use a new pan gasket and filter seal, refill, and clear the codes so you can verify the shift solenoid commands with a scan tool.