I posted all this in the HEADLIGHT RELAY !)! thread but Im posting here as well cause its relevant.
i spent a LONG time under the dash last night and I finally figured out why Ive never seen that diode.
cause I dont have one.
but the funny thing was- my headlight buzzer and my key in buzzer work and that didnt make sense. so I looked and traced it all out and I figured out how MY system works and its nothing like the schematics posted or in my service manual or the posts up above.
Someone might recogize the setup in my car and let me know WHAT THE HECK IS GOING ON. or it could just be jimmy rigged. im thinking it was jimmy rigged
under my dash, theres that black molded connector (Black) shaped like a T just like they show in the service manual schematic.
There are 2 Black /w yel wires and 2 Red wires going to the T connector. one red goes to the steering columm key switch and the other red goes to the key in buzzer so when the key is in theres power to the key in buzzer (since these wires are tied together)
But the mating connector is NOT the diode connector like its shown above. Theres a short (about 4" long) harness connected to it with T connectors on both ends with 2 yellow wires (which connect to Reds above) and a Red wire
(which connects to the blk /w yell wires above).
One of the two yellow wires goes into a harness (and that goes into a relay with some grn and a pink wire. I have no idea what it does) but the other yellow wire and Red wire run about 4"s to another T connector. That connector has a longer cable hooked up to it which is about 12" long. that cable is 2 wires- a blk and a yell wire.
It ends at a relay looking thing mounted to the dash frame by the radio. I figured out that its a replacement the diode (or at least works like one). I'm not sure if its a factory replacement, an upgrade of some sort, or possibly from a later year harness, or just something the previous owner jimmy rigged to replace a blown out diode. Im betting on the latter just by looking at some of the other wiring mods to the car.
So, when the lights are on, power comes from the Blk /w yell wire to that relay and energizes it. It closes and sends that 12v to the yellow wire that goes to the Red wire for the key in buzzer.
with the lights off, the relay is open so the key in the ignition doesnt backfeed the light switch or the lights when IT powers up the buzzer.
Here is a diagram of what I found.
https://board.moparts.org/ubbthreads/upload2/4795802-headlightwarningcircuit.pdf
...Dug out an old connector and wired/soldered the diode in place...Take note which way the diode band needs to face to block the backfeed current...The paper is a reference for the diode placement and direction{from the FSM}... 
... And lastely the finished product gets wrapped with some cloth tape and I made up a tag for ID... 
Total cost less than 5 bucks !!!! 
.... 
.....Judging by the literature you've posted...The increased cost for the stand alone headlight delay compared to the AO1 package would lead us to believe it's the cost of the diode that would already be in place with the AO1 package....But it seems not all AO1 cars actually got the diode... 
And the research continues.... 
.... And here's a pic of the 70 roadlamp harness....Take note that the connector marked "headlight warning buzzer" does in fact plug into that connector and in turn has another plug for the diode to do it's job... 
