Weird AC and Headlight issue

Woop, my bad. Yes, Gen 2 has a dual pressure switch. You're not seeing two switches because they're built into one assembly. You can see it in the B1423 section of the Gen 2 manual (which is only four pages, not fifteen like Gen 3).

 

Yet more incentive to "diagnose twice, cut once."

 

A long shot. But maybe look up wiring schematic see if the headlights and a/c share a ground point ?.
You mentioned the high side/ discharge line been warm not hot to the touch?
1: was this right at the compressor discharge line
2: or the smaller line after condenser?

If you have a contact type thermistor temperature sensor. (“ NOT A INFRARED“) take the TEMP at the line at top entering the condenser. Then the line exiting the condenser. The temperature should be less than 50° difference but more than 20° difference

What is the TEMP at the line just coming out of the compressor?
What is the temp of the suction lung returning to the compressor.
Note: if you do try to use an infrared thermometer do not try it on the thin little lines you do not get an accurate reading .
Some black barbecue grill flat paint sprayed just at the entrance of the line going from the compressor to the condenser about the size of a Silver dollar. And then spray black flat spray paint on the condenser around the exiting line of the condenser. Now you can take more accurate temperature measurements using a thermal infrared sensor gun.
1: Test should be performed with the vehicle out in the sun for a load
2: all doors and windows open with air selector on fresh air mode blower motor set on high
3: take your pressure measurements high side and low side within accurate gauge 2% or less and I can guarantee you these gauges are not sold on your normal automotive gauges and they are rarely accurate after the first few times have been dropped and just use and age.
4: compare your pressures to your PT chart
R134A pressure temperature chart - Google Search:
5: take your temperature is about 5 to 10 minutes after the vehicle has been running constantly I’m talking about the compressor in the situation .
6: your high side pressure reading with the temperature of the small liquid line located next to where you take your pressure should match up closely within a few psi
The same goes for your low pressure reading at the suction line and the temperature within a few inches of the suction line port should also refer very closely to the PT chart
If not there’s definitely something wrong also make sure your cabin air filter is clean or new even a little restriction makes a difference .
The above test have nothing to do with your intermittent problem but I can give me a clue of the accuracy of the refrigerant charge. Just two or 3 ounces either more or less make a huge difference on a Prius specially more in a very hot climate .
Another note if the vehicle was ever in a front end collision in the condenser had to be replaced they sometimes use aftermarket condensers some of them are good and some of them are not they have few were cooling fans per inch and fewer refrigerant cooling passages tubes. This greatly affects cooling performance in hot weather. But you may not notice anything in more mild climate .

 

Can I ask how you determine the ballast is failing? Curious to know since 2 or our 3 family gen 2s have HIDs.