The "X" Circuit from the Ignition Switch.
What is "X"?
"X" is the terminal of the ignition switch that's working while your car is starting and the headlights, wipers and HVAC fan go off.
Here's a pic, hopefully it'll explain most all of the circuit.
Understanding that circuit saves a whole lot of puzzlement [s]if[/s] when there's a failure of headlights, wipers and HVAC fan in various combinations.
1st, lets follow the power flow through the schematic on a car with all systems good.
Battery power is available to BOTH the ignition switch AND the switched circuit of the load reduction relay.
Switch the ignition to the RUN position and power flows through the black/yellow wire activating the load reduction relay solenoid coil, making power available to the wipers, HVAC and rear defogger. At the same time, power is also switched directly to the headlight switch, which can then be switched to the High/Low beam dimmer switch.
It is worth mentioning the parking/running lights at this point, they are on a completely separate circuit from the ignition switch and the "X" circuit, you've probably noticed that the parking/running lights work whether the key is switched on or not. Electrically, the parking/running lights have absolutely nothing in common with the headlight circuit even though the headlights and the parking/running lights are operated by the very same switch.
There are several possible failure modes through the "X" circuit that are generally easy to diagnose fairly accurately just by the symptoms present.
If everything downstream of "X" on the ignition switch, that is headlights, HVAC fan, wipers and rear defogger are all inoperative, it is reasonable to assume that "X" on the ignition switch itself has failed.
There are several possible ways to test for this condition.
The most conclusive way to test is to unplug the ignition switch and bridge battery power from the red battery power wire to the black/yellow "X" terminal wire, then check to see if all the downstream components are operative.
Alternately, one could test for power at terminal 86 of the load reduction relay socket with the key switched on and the relay removed.
One could also bridge the terminal 30 to the terminal 86 connectors at the load reduction relay socket with the relay removed and then check and see if the headlights work. Next bridge from terminal 30 to terminal 87 and see if the HVAC fan, wipers and rear defogger work.
If the headlights work but the HVAC fan, wipers and rear defogger are inoperative, the load reduction relay itself is usually at fault. Put one hand on the load reduction relay and switch on the key, the relay should be felt to click on and then click off as a key is switched off. Bridging terminal 30 to terminal 87 will also verify that most of the rest of the circuit is good. Use a multimeter or a test light across terminals 85 and 86, there should be power showing whenever the key is in the wrong position. Don't confuse relay clicks from the fuel pump, glow plug or DigiFant power supply relay(s) for load reduction relay clicks.
If the headlights do not work but the HVAC fan, wipers and rear defogger work, the problem is most likely in either the headlight switch or the high/low beam dimmer switch.
It is also possible for the "X" terminal contacts in the ignition switch to be burned in such a way that adequate current will be available to operate the load reduction relay but adequate current to operate the headlights cannot flow. If this condition were present, I would expect the HVAC fan, wipers and rear defogger to operate normally, but they would probably switch off as the headlights were switched on.