Written By: 'chu@hanauma.jpl.nasa.gov' (BNR400)

This is common problem with the lame wiring used in the lights. The power for the fog lights is taken directly off of the low beam power. This follows that laws about fog lights being on only with the low beams. But, this draws more current from the lights wiring than they can handle, and it also overloads the switch contacts. What's happening is the thermal shutdown in the switch is tripping and resetting. I've also found that the overheating hardens the plastic levers that actuate the switch contacts, and they break off.

I've just figrued out how to install a set of relays and heavier wires in my car to switch the fog lights separately. I'd be working on it if I was at home instead of Fairbanks. Anyway, the wiring harness runs through a black round connector with two rows of 4 pins. It is secured to a place just below the battery tray. This is not either of the two connectors near the ignition coil, though they all look very similar.

The wire that feeds the fog lamp switch is a 16 guage wire with a yellow insulation and a black stripe that comes from the brights switch, originating From the headlight low beam switch. It first goes to the fuse block through a 15 amp fuse and comes out as a light blue with black stripe 18 guage wire to the fog light switch. Out of the fog light switch is a tan with orange 18 guage wire that ultimately leads to the headlight wiring harness through an 8 pin connector located just below the battery tray. I don't remember the current carrying capacity of 18 guage, but it is 2 sizes too small to be protected by a 15 amp fuse.

What I did was intercepted the connectors at the battery tray. I found a couple of matching connectors from the engine wiring harness that I got off of a salvaged car which mated properly with the lighting connectors. I jumpered all the wires between my new connectors except for the wires for the fog lights and the brights. For these, I connected the ends coming from the switches to power relays, which in turn switched power obtained directly from the battery through some 12 guage wires and 20 amp fuses I hooked up, which then fed the connectors on the lights side. The relays I got were Radio Shack PN 275-226, which look remarkably like the ones Bosch uses in their auxilary lighting systems. These things are rated at 30 amps. For a really secure contact, I drilled holes into the spade terminals and attached all the wires with eyelet lugs using 4-40 stainless cap screws. I also wrapped all the contacts in silicon rubber and then heat-shrink tubed them for weather protection. There is a small bulge in the battery tray, under which was enough room to mount up to 4 of these little relays. I put my two relays there and routed their wires toward the back of the tray, where they intercepted the stock lights connectors. They now give me the greater current handling capacity without my having to actually cutting up or splicing into the stock harness. Plus, if anything ever went wrong with the relays for any reason, I could take them out of the circuit by simply reconnecting the stock connectors in the original manner.

Not only I can now run both the low beams and the fog lights without overheating my light switch, and I could even get brighter bulbs for either of these lamps without worrying about overheating the wirings. I guess 20 amps working current capacity for each circuit is good enough for a 100 watt filament in each of the 4 lamps. Oh yes, I've also replaced my underdrive crank pulley with the stock unit, to avoid any possible charging problems.

The one thing I wish I could have done was to replace the headlight harness as well, since the fog light wiring is still 18 guage, and the headlight wiring is still 16 guage. This would have required buying raw connectors from Ford and building them myself from scratch. As it was, my job took me 8 straight hours because I was developing it as I went along, changing my plans about 3 times. If I were to do it again to a different car, I'm not sure if I could stick to an original plan without first having taken the car apart to see where everything was. But for now, it works.