So I've been wondering about what these are all about. I know about the 9 pin.
Thanks
On our '97 the rectangle plug is for a direct contact to the trans. ECM. This is where you can go in and change all kind of settings on the World trans. series along with troubleshooting in depth that don't go through the engine ECM link. The 2 ECM units talk to each other all the time. The triangle is somewhat different than ours but looks similar. Our plug like this is to the ABS computer which those changed from year to year.
Mike
Left to right is the ALDL connector, CAN terminating resistor and 9-pin J1939 interface.
ALDL is an old GM connector, it's mainly there to support older transmission diagnostic tools.
The CAN terminating resistor is a 120 Ohm resistor in a Deutsch housing.
The 9-pin is the SAE J1939 standard interface that is more popular now for diagnostics.
The ALDL is part of the transmission wiring harness and just connects to the transmission for diagnostics.
The 9-pin has both J-1939 and J-1587 CAN networks. The J-1587 is the older slower standard. The gauges use that. The J-1939 connects to all the other ECMs and would give data from ABS, Trans, or Engine ECMs.
The terminating resistor is just part of the wiring standard. CAN networks wire all ECMs in parallel and have 120 OHM resistors at each end. The other one should be back by the engine and there is another 9-pin connector back there.