When Hella came up with their 90 mm modular lighting series a few years ago, my friend Reinhold quickly saw the possibility for a low profile headlight alternative for the Fiero that was road-legal here in Germany. There was even a choice of H7 projectors or HID projectors with identical mounting.
Prototypes were quickly built from laser-cut and welded sheet metal, and the results were literally beautiful. The headlights only opened half as high compared to stock, and the H7 projectors make night into day compared to the stock sealed beam or H4 headlights. Others picked up the original idea, and now there are at least two sources of these headlights. I got mine from Timo of Fiero Europe. There is also a source in the US, but I've never seen those units myself.
No matter which headlight you choose, upgrading from dual filament headlights has one big advantage. With both filaments in the same bulb, you can't have both high and low beams on at the same time. If you try anyway, you'll blow the bulb. Not so with a H7/H7 or H7/HID setup. Since the light sources are separate, they may be on simultaneously. An additional benefit with the use of HID is that when flashing your high beam, the low beams go off and come right back on when the high beams go off. Since HID has a high voltage generator that has to ignite an arc again, this situation is not ideal. So what we really want is the low beams to stay on independently of the headlight dimmer switch.
Now, at first sight, it seems like this is an easy task. Add a jumper wire to short the headlight dimmer switch. Simple, eh? But this is not a great idea, and here's why. The magic word is "current rating" (ok, so two words actually). Each H4 bulb is rated 55 Watts, or roughly 5 Amps. So the headlight wiring was designed for a total of 10 Amps, and our modification would double this to about 20 Amps with both high and low beams on at the same time. That's quite a bit of current, and if a wiring's current rating is exceeded, the wiring may blow like a fuse or catch fire. Fieros are said to burn beautifully with a bright orange flame, but I'm not eager to try this out. Even if the wiring doesn't go up in flames, any headlight related problem is likely going to happen at night (why else would you have your headlights on?), and if your vehicle suddenly goes dark, another car could collide with you.
Another reason why this is a bad idea is voltage drop. The more current you draw, the more voltage (and thus power) will not reach your headlights. If your total headlight wiring (including your 25 year old wiring and possibly oxidized connectors) has a 0.25 Ohms resistance, at 20 Amps current draw you're losing 5 Volts, and only 8.8 Volts would reach your headlights, almost only half of your 13.8 Volts. With H7 bulbs, this will only cause your headlights to be dimmer than they could be, but with HID it may keep your HIDs from igniting, because both HID controllers powering up at the same time can cause a voltage drop large enough for one of them to stay dark. I've seen it happen!
Since the reliable operation of your lights is crucial, I suggest keeping the rewiring to a minimum on the low-beams, because each extra splice, connector or relay is a potential failure point that may cause your car to go dark. However, if the high-beams fail, it's not such a big deal. So keep that in mind.
Now, the first thing we notice (and I'm looking at the 88 manual) is that the grounding is pathetic. First of all, the ground wiring is only 0.8mm wiring where the rest of the system is 1mm, and the it first goes to a splice near the bulkhead connector before going to a ground. Bad for H7, catastrophic for HID. So I wired a new 1.5 mm ground wire for each side to go to a new 2pin Weatherpack connector for each low beam. Reason being that if you ever want to go HID, this direct, low resistance ground is way better than 10ft of 0.8 mm wiring.
The tan (hot) 1mm low-beam wire can be kept, because feeding new wires into the harness under the radiator is a pain. Since the tan wire goes to the LH side headlight connector first, and from there to the RH side, we need a splice because you cant feed two wires through a weatherpack seal. I spliced the wires in the main harness and now there's a Weatherpack low-beam connector in case I want to go HID. With this connector I can switch easily between H7 and HID, but if you want to go HID only, you can use the proper connector for your HID control module instead of the Weatherpack solution.
My high-beams came with a separate parking light bulb, so I chose a 3 pin Weatherpack connector for parking lights, high beams and ground. Except for the parking lights, which I had to route to the headlights, I used the already existing Fiero wires, i.e. the old headlight ground and the old high beam wire (lt green). As with the low beam, the two-wire crimp at the LH headlight connector must be replaced with a splice in the main harness, and the extra parking lights ground is spliced to the high beam ground to prevent the use of an even larger 4-pin Weatherpack. Besides, the small 2W parking light's current draw is negligible so it can share the high-beam ground.
The passenger side is simpler than the driver's side, since there is only one wire at each terminal. Just change over to Weathepack terminals and add the extra 1.5mm ground wire for the low beam.
That's all in the front compartment! Now both high and low beams have separate wiring of at least 1mm, up to the bulkhead connector, C100.
Before we start here, let, let me say that we will need to access C100, separate it and move/remove some terminals. You can read more about C100 here.
Looking at the wiring diagrams for the inside of the Fiero, we notice two things: 1) there is no headlights fuse but a circuit breaker in the headlight switch, and 2) the headlight switch's output goes to feed the headlight dimmer switch, and also control the headlight module opening the headlights.
The former supports us in the conclusion that it's a bad idea to double the current draw because all current would go through the headlight switch's built-in circuit breaker. The latter shows us that the yellow headlight circuit is where we need to start. If you switch the tan J7 and yellow J9 circuits in C100, you circumvent the dimmer switch, and the yellow 1mm wire will feed your headlights, no matter if the high beams are on or off! Now, this is exactly what we want, but it means that now the headlight won't come up if the high beams are on. While this wouldn't be so bad, I suggest cutting off the tan terminal and splicing it to the yellow wire. Now the yellow wire will feed both headlights through J7 and control the headlight motors through J9. For this splice I didn't cut the yellow wire that now goes to J7, but only stripped its insulation and soldered the tan terminal wire to it, keeping the wire intact. Isolate and tuck away the open end coming from the dimmer switch.
We now have low-beams that stay on independently from the high beams, and keep the headlight switch circuit breaker, but we need to draw power for our high beams elsewhere. Let's put in a 15Amp high-beam relay! So, I put a relay socket in and taped it to the harness going to C100. Cut the light green wire going to J8 and crimp a relay socket connector to it, going to the relay's coil. Get a new 0.8 mm wire (black) and wire it to the other side of the relay's coil. Connect this wire to a ground. Crimp a new Metripack terminal to a new light green wire, insert it into C100 cavity J8, and wire it to one of the relay's normally open contacts. Now our headlight dimmer switch feeds a relay instead of the high beams, the additional load on the headlight switch's circuit breaker is insignificant. And our relay's output feeds the high beams.
All that's left to do is feed some fused power to the high beam relay (the remaining relay contact). There are a few possibilities:
HID/H7 headlights are a great way to modernize your Fiero, make the car look better, and you won't believe the difference in lighting these new headlights make.