It's no secret that the the quickest way to massive numbers of broverlanding points is by adding more lights. Light bars, rock lights, ditch lights, reverse lights, amber lights, raptor lights, camp lights, interior LED lights - you name it, and you can drop a few hundreds or thousands of dollars to make your truck look lit - literally - in daytime photos.
That's not what this mod is about. I mean, it's about auxiliary lights, but it's about how to make them more functional. Specifically, how to make it so that extra light can be switched by both your hi-beam switch as well as a manual switch.
Like most, when I installed a couple of Hella lights on my bumper (500's at the time, but replaced with 700's after we hit a deer on the way back from Death Valley), I wired them up to a switch that I put on the dashboard. At the time, I just used a simple push-button switch, and whenever I wanted the additional light that the Hella's afforded, I'd press the switch and voila!
Life was good for all of about three uses. It was at that point that I realized that I almost always wanted to turn on the Hellas at the same time I turned on the hi-beams - almost always for night driving on the freeway, so I could stand a little better chance at spotting a deer before it jumped out in front of the truck.
That was over three years ago! And I've done a lot of night driving since.
With a few other projects I've been procrastinating even more than this one, I figured that today was the day to finally make things right. But before I get into the details of the job, let me outline a bit about how the electronics here work.
Relays
Nearly all automotive lights - whether they are OEM or aftermarket - are not switched directly from the battery. That is, there's not a wire that runs from the battery to a switch, and then to the light, and then back to the battery (ground). Doing so would cause a lot of current to flow through the entire circuit, and that can cause the wires to overhead - leading to a vehicle fire. No good!
Instead, relays are used. A relay is essentially a second switch in the circuit, and it's turned on/off using an electrical signal - usually from a switch in the cab of the vehicle. That allows the circuits in the cab - where we especially don't want fires - to have less current flowing through them, and for the larger amounts flow through larger wires that are in the engine bay.
Normally, an auxiliary light is wired directly to the battery as shown in the diagram above - allowing the user to flip the switch whenever they want in order to turn on the lights. But what I needed was a way to have two switches control the lights - one that would turn them on whenever and one that would turn them on only when the hi-beams were on.
And that meant that I needed to find a wire in the truck that only had power when the hi-beams were on. Diagrammed out, it needed to look like this:
Luckily for me, I found that wire. On a 96-04 Tacoma - as well as many other vehicles - there is a wire specifically for hi-beams going into the headlight. So if you find yourself in a similar situation, here's how to install a switch that allows you a bit more control over when your auxiliary lights turn on!
To get started, I needed access to the electrical connector going into my driver side headlight. That meant removing the battery and disconnecting the plug - simply by pulling it out. Then, after cleaning off the wires so I could better identify them by color, I found the black+yellow wire, which the wiring diagram for my truck indicated was for the hi-beams.
With the wire accessible, I used a wire tap/splice to connect a new length of wire that I ran back through the engine bay and through a grommet into the cab.
From here, I hoped I'd be able to simply remove the ON-OFF toggle switch I'd been using and connect the new ON-OFF-ON (SPDT) switch I planned to use now, but alas - the space behind the dash was too tight to pop out the switch. So, dash disassembly (see Removing the Dash Trim) was required.
With the dash removed, I was able to get the old switch out and connect the new switch to the two existing wires - one of which went to the relay, and the other directly to the battery - and then the third, new wire, that I'd just installed. The wire that would supply power only when the hi-beams were on.
With that, all the hard work was done and it was just a matter of installing the switch into the existing hole, putting the dash back together, and re-installing the battery. A quick test showed everything was working exactly as it should - the hi-beams now also controlling the Hellas.
Success, mostly. 'Cause well, I did have this left over at the end of the project, and I know just where it goes. 
Something to take care of the next time I remove the dash.
Update as of January 10, 2020
So, the new switch is working great when the headlights are on! When the low beams are on, the Hellas are off; when the high beams are on, the Hellas blast the light forward as well. But - and you knew there was a but coming - I do have an issue that I just can't explain.
When the truck warms up and the engine is at operating temp, if the switch controlling the Hellas is in the "come on whenever the brights are on" position, the Hellas also come on when the parking lights are on - that is the headlights themselves are completely off. Somehow in this state, enough current is flowing through the circuit to trigger the relay, or the resistance of the relay when warm is reduced, causing it to flip on.
I don't drive around with just my parking lights on that often, so it's not a huge deal, but it's something I want to get to the bottom of eventually.
Update as of October 28, 2020
Well, I've solved the problem. And, it turns out the problem was something I did to the truck nearly 20 years ago! My first mod even - disabling the Daytime Running Lights. For a description of what was going on, and how I fixed it, check out the full story: *Fixing* My First Mod - Really Disabling the Daytime Running Lights.
That spare screw fills the hole in your head! UJ