The standard operation of the MkII MR2 fog lights allows operation only when the low beam headlights are on. It is possible to modify the fog lights so that they are operated solely by the fog light switch, or so that they are operated by the fog light switch whenever the running lights are on (but independent of the headlights). If they are tied to the running lights, then the circuit that turns off the running lights when the car is turned off and the door is opened will also turn off the fog lights.
First off, I have a '94 model and I have made the modification to operate with the running lights. I believe that there is a slight difference in the wiring of the '91-92 that simplifies the modification somewhat.
Follow the circuit on the '94 wiring diagram: The fog lights are controlled by a relay in the front trunk (on the right side). Control of the fog lights is accomplished by controlling this relay. As shipped from the factory, the control circuit is powered through the high beam filaments, through the relay coil, then through the control switch. In the '91-92 models, the other side of the control switch is routed directly to ground (or so it appears), but in the '93+ models it is routed through the retract control relay (on the left side in the front trunk), through the headlight switch, and then to ground. One side of the high beam filaments is connected to +12 when the headlight switch is on (either high or low beam). The other side is switched to ground when the high beam is on and left floating when the low beam is on. Thus, when the low beam is on and the fog light switch is closed, a small current flows through the high beam filaments and then through the fog light relay coil and then to ground. The current is so small that it is not noticeable.
The first part of the modification is to supply +12 to the fog light relay under the desired condition. If you want the fog lights to be independent of all other lights, you can disconnect pin 2 on the relay from the red w/ yellow stripe wire leading to the headlight circuit and connect it instead to pin 4 on the relay which is connected to a red w/ black stripe wire supplying +12 to the fog lights themselves. This can be done under the socket by cutting and splicing the wires there, or by bending pin 2 of the relay itself and splicing it to pin 4.
If you want to connect to the running light (tail light) circuit, this is best accomplished by making some splices in the wiring harness. The harness is below the relay panel, and you must unwrap some of the tape from around the harness. Follow the red w/ yellow stripe wire from the relay panel to where it splices into the red w/ yellow wire leading to the headlights (splice point B6). Cut the wire leading to the relay panel at the splice. Now, within the same harness, find the solid green wire leading to the front running lights. (Note that there is another solid green wire that runs to the front right and is part of the headlight retraction system. You do *not* want that wire. Either check the wire with a volt meter to make sure it gets power with the taillight circuit, or look for a splice in the wire -- the taillight circuit is the only green wire with a splice within the harness.) Splice the red w/ yellow wire from the fog light relay into this green wire. Be sure to make a solid connection (solder it if you can). Tape up the connections, then re-wrap the harness with the electrical tape and re-attach the relay panel.
Try things out. If you have a '91-92, or whatever year has the downstream side of the fog light switch connected to ground, the fog lights should work as desired. If your switch is routed through the retract control relay, the fog lights will now work whenever the headlights are on, regardless of the high beam/low beam setting. In that case, go to the left side of the front trunk and find the red w/ black wire leading to pin 17 on the retract relay. Cut this wire from the relay and splice it to a ground wire (there are several handy at the relay). The ground wires are white w/ black stripe. This should break all dependence on the headlights.
marcus hall '94 MR2T - Solar Yellow!
So I drew up this modified schematic.
The mod itself is really easy, so I don't see what all the confusion is about.
- Jeffrey Ho See
I recently decided to finally do the fog light modification to my MR2 and was reading through the well known instructions on MR2.com. I realized that
there were two scenarios listed in at least three places. Either running the fog lights with the parking lights, or completely independent of anything
but the battery and fog light switch. The later is close to what I wanted but I didn't want to have the possibility of leaving the fog lights on and
draining the battery. I wanted the fog lights independent of the headlights and parking lights but only on when the ignition was on. I made some
inquiries and found an answer that worked.
The answer comes from Ricky Benitez on the MR2 message boards:
This should be a simple mod. The fog lights already have their own relay and fuse in the front trunk fuse box. The red wire w/ the yellow strip going to
this relay comes from the headlight circuit on US cars to provide positive power to the coil. The switch on the console provides ground when closed to
turn on the fog lights. If you cut the red/yellow wire and tap it to the black/orange wire going to the main fan relay in the same fuse box you will
then provide positive to the relay coil only when the ignition key is turned to "ON" (but not in "ACC", so you can play the stereo in the parking lot
without having the lights come on). This means your fog lights will then come on when the ignition key is turned to "ON" and the fog light switch is
on.
For Canadian cars the whole she-bang is wired differently to comply with their headlight laws, so this mod does not apply there.
This mod worked on my '95T and Ricky has a '91 so the advice should be universal for US MR2's
- Garrick Heuer
