89-93 Thunderbird SC Fog/Driving Light Rewiring Instructions

Raymondo

Registered User
Well I finished the rewiring of my Fog/Driving Lights yesterday and thought while it was fresh in my mind, I would write up detailed instructions and share. I gleaned parts of my work from http://www.sccoa.com/articles/foglights.php and http://www.35thatr.org/Fog/RewireFogs.htm. I hope this helps someone in some small way. :)

Materials Needed: Two (2) Inline Fuse Holders (recommend weatherproof), One (1) 40 Amp Relay, Eight (8) feet of 12 gauge wire, Four (4) Insulated Female Plug Connectors, Five (5) Blue Butt Connectors, Two (2) Wire Caps, One (1) Blue Crimp Connector, One (1) Insulated Large Circle End Connector, One (1) Insulated Split End Connector, One (1) Roll of Electrical Tape, One (1) Assorted Package of Small Fuses.

Tools Needed: Medium Size Phillips Head Screwdriver, Small and Medium Size Flat Blade Screwdriver, Wire Cutters, Wire Stripper, Volt Meter or Test Light, Crimper, Hobby Knife, ½” or 7/16” Open-end Box-end Wrench, ¼” Drive Ratchet, 6, 7, 8 mm sockets, 5/16 socket, Permanent Marker.

Step By Step Instructions:

1. Remove the top of the Console – Begin by removing the three screws just under the Console Lid. Ease that end of the Console Top up to gain access to the Ride Control and Fog/Driving Light Switches. Using a small Flat Blade Screwdriver pry up the locking tabs on the connectors and slip the connectors from the switches. Once that is done, pull the Parking Brake all the way up and either shift the transmission into Neutral (Manual) or Low (Automatic). The Console Top should slip off, front end up, with a little effort. Be careful do not to force anything. Be patient. (It is possible that the Automatic Shifter Handle may have to be removed and some models have an ashtray light that may have to be removed.)

2. Remove Lower Dash Trim Panel, Plate, Steering Column Collar – Begin my removing the screws on the bottom of the Dash Trim Panel (this panel is just above your knees and just below the steering column). There is also a screw on the left side near the door, remove it as well. The Trim Panel is held on my Four (4) Spring Clips; apply steady pressure to pop them out. DO NOT pry or yank on the panel as you risk breaking off the Spring Clips or cracking the Trim Panel. Once the Trim Panel is removed, remove the metal plate behind it – three screws. Then remove the Steering Column Collar by removing three (3) Phillips head screws that are recessed in the bottom of the collar. The top and bottom of the collar also snaps together, so gently tug them apart.

3. Running Power Wire to Factory Fog/Driving Light Switch – With the previous items removed, pull the headlight switch on and with the Volt Meter or Test Light determine which wire on the Fog/Driving Light connector is hot and mark it with the Permanent Marker: it should be the only one with power to it. Next, turn on the Ignition and using the Volt Meter or Test Light determine which wire(s) in the harness running from the switch are hot and mark one. Now, Turn Off the Headlight Switch and then cut the wire about halfway between the connector and the harness end. Cap off the end of the wire extending from the harness with one (1) Wire Cap and wrap it with Electrical Tape. DO NOT cut the wire in the Ignition Switch Harness. Take approximately 3 to 3 ½ feet of 12 gauge wire and connect one (1) empty Inline Fuse Holder to one end with one (1) Blue Butt Connector, wrap the connection with Electrical Tape. The new power wire is now complete. Trim the end of the wire extending from the Fog/Driving Light connector and connect it to the Inline Fuse end of the new power wire, wrap the connection with Electrical Tape. Route the new power wire underneath the console and extend it under the center Dash Pillar. (It is recommended that the new power wire travel under the inner edge of the console as a preventative measure.) Route the new power wire through the under carriage of the dash and connect it to the marked hot wire from in the switch harness with the Blue Crimp Connector. The new power wire is now complete, except for adding a fuse to the Inline Fuse which will be the last step in this installation.

4. Prepare Factory Fog/Driving Light Harness – Locate the wiring harness for each Fog/Driving Light, twist out the bulbs from the light housing, disconnect the bulbs from the harness, unsnap each harness from the frame of the car and from the top pull each harness up until they are completely exposed. On each harness, peal back the factory tape beginning at the radiator support revealing the plastic conduit for about 6 inches. Inside each conduit are one black wire and one tan wire with an orange stripe: the black wire is the ground it will be left untouched. The tan wire with the orange stripe is the factory power wire. On both sides of the car, cut this wire into about halfway down the exposed 6 inches. On the Passenger Side cap off the end of the wire extending from the car side of the harness with one (1) Wire Cap and wrap it with Electrical Tape. With the Light End of the harness, strip back about 3/8 of an inch of the insulation and connect it to one end, which has been similarly stripped, of the remaining 12 gauge wire with one (1) Blue Butt Connector, wrap the connection with Electrical Tape. Route this wire underneath the hood latch brace to the Driver’s Side of the car.

Now, cut off about one (1) foot from the 12 Gauge wire routed from the Passenger Side, cut into three (3) even pieces, strip all six (6) ends about 3/8 of an inch. Take one of these pieces and connect it to the remaining empty Inline Fuse Holder with one (1) Blue Butt Connector, wrap the connection with Electrical Tape. Connect the one (1) Insulated Large Circle Connector to the other end of the Inline Fuse. (This will be the Power Wire for the Relay) Take the second piece of wire, connect one (1) Insulated Female Plug Connector to one end and one (1) Insulated Split End Connector. (This will be the Ground Wire for the Relay) Take the last piece of wire and connect one (1) Insulated Female Plug Connector to one end.

On the Driver’s Side strip back about 3/8 of an inch of the insulation on the wire extending from the car side of the harness and connect one (1) Insulated Female Plug Connector. This wire will carry the signal from the Factory Fog/Driving Light Switch and turn on the relay that will be installed. Strip the end of the 12 Gauge Wire routed from the Passenger Side about 3/8 of an inch and attach one (1) Blue Butt Connector. With the Light End of the harness, strip back about 3/8 of an inch of the insulation, and the last piece of wire from above, and insert both wires into the open end of the Blue Butt Connector attached to the 12 Gauge Wire routed from the Passenger Side.

Go back and reinsert as much wire as possible in the plastic conduit in the Fog/Driving Light harness and wrap it with Electrical Tape.

5. Mount & Connect Relay – The 40 amp Relay will have four (4) posts: one for a ground wire, one for power, one for a switch and one for lights (output). Connect the Relay Power Wire constructed earlier to the Power Terminal of the Relay and to the Car Battery, routing the wire through the Radiator Support. Connect the Ground Wire constructed earlier to the Ground Terminal of the Relay. Connect the Tan and Orange wire with the Insulated Female Plug Connector on the Driver’s Side to the Switch terminal of the Relay. Connect the wire extending from the connection of the 12 Gauge Wire routed from the Passenger Side and the Light End of the Harness on the Driver’s Side to the Light or Output side of the Relay. Attach the Relay to the Radiator Support just below the top of the support and behind the Driver’s Side headlamp. Connect the Split End Connector of the Ground Wire to the Radiator Support with a metal screw. Installation is now complete.

6. Final Steps – Route the Fog/Driving Light Harnesses back toward the Light Housings, reconnect the Bulbs to each harness and reinsert the bulbs into the light housing. Reassemble the Steering Column Collar, Lower Dash Panel and Trim. Install one (1) 20 amp small fuse into the Inline Fuse Holder attached to the Fog/Driving Light Switch Connector, then reinstall the Console Top, taking care to reconnect the Fog/Driving Light Switch and Ride Control Switch. Install one (1) 20 amp small fuse into the Inline Fuse Holder attached to the Car Battery. With the Factory Fog/Driving Light Switch turned OFF, start your SC, then turn on the Factory Fog/Driving Light Switch. Your Fog/Driving Lights should be burning brightly.
 
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fogs

question? did you do all this so that the fog lights actually burn brighter, or was there an original corrosion problem.
 
Most people rewire the early model's foglamps to prevent the OEM Switch from melting like they often do given all of the current running through the switch. The later models 94-95's use a relay to prevent that problem stock from the factory.
 
which switch do you refer to...... the multi function headlight or something different?

If you are referring to Duffy's post, it is the multifunction headlight switch that tends to overheat and burn out, hence the rewiring of the Fog/Driving Lamps.
 
Actually it is the Fog Lamp Switch I was referring to and the one that melted on my 92 along with a portion of the connector to the switch.
 
Actually it is the Fog Lamp Switch I was referring to and the one that melted on my 92 along with a portion of the connector to the switch.

Wow, really? I have never had that happen. I have always had the headlight switch fail. These cars do keep it interesting do they not? :D

Anyways, that is why I rewired mine in the manner that I did; to take the load off the factory stuff and place it on a relay switch. And why I used two inline fuses.
 
Hmmmm. well i already replaced the multi function switch. wasn't even aware of that switch having problems. my 92 seems fine...er, aah .. so far.
 
I know this is probably such a dead post but I figured I would ask a question about the lamps. I have been searching around for some info on the fog lamps and on tccoa a few guys mention the stock wiring cannot handle a newer higher wattage bulb. Is this true? if so has anyone ever rewired the lamps to handle anything with a higher wattage?
 
Yes it is true for the early models. The 94-95 SC's used an auxiliary relay if memory serves. I use Hella Foglamps which are 55W bulbs in each. I use an auxiliary relay to control them. I use the stock wiring to control the relay only.
 
To add to your wright up if you use 12 gauge wire you should use the yellow spade connectors and not the blue ones. Yellow are for 10-12 AWG wire and blue are for 14-16 AWG.

For the signal form the switch the blue are fine but should not be used on the power side.

Before someone says the blue fit--I know in some cases they do but should not be used.
 
Ok, I am asking a question maybe answered in other areas but here goes...

Did the early model wiring actually provide the POWER through the main switch, then through the og Light switch and direct to the lights themselves?

Is that why they burnt out the switches? FULL 12V power with Amps running through the switches, all that draw on the little wiring and switches?

That is why the later models used a relay?
Was the relay activated from the fog light switch but POWERED from a seperate large wire for the direct power to the light?
 
Relays

If you take a look at any newer car/truck almost everything uses relays.
My wife's H2 has a million of them! Most of your fog light kits come with relays these days. Using a smaller wire size to provide 'signal' pwr to the switch then the relay saves weight and is safer due to shorter length/fewer connectors that have to handle high current. In a new car there are loads of relays in the engine bay, many connected to circuit breakers instead of fuses. But look at the size of the fuses in the engine bay fuse panel, holy crap! Those are some big fuses.
In my work (military pwr gen/electronics) we use a load of relays and contactors for the same reason. All the control circuitry is low voltage (28VDC/AC-115VAC) controlling 450VAC/3ph up to 700VDC by way of relays and contactors.
When I put fog lights on the rear of my truck, I ran power wire from the battery to a relay (built in 30A fuse) then to the back of the truck. Then I ran a 'signal' wire (14ga. with fuse) from the reverse circuit to toggle sw. to the relay. This allowed me to turn on the fogs when I needed extra light when backing up (no street lights). By tapping off the reverse circuit, this enables the relay only when the vehicle is in reverse (safety for the vehicle behind you).
Most states have laws that require your wiring to be such that your fogs can only come on when: Parking (minimum) or lo beam headlights on. Off when hi beams selected. Same with driving lights, except only work when hi-beams on, off at all other times. The after-market relay kits have been out there for decades.
If you do the relay install: it saves wear and tear on the multifunction sw., the fog light sw. and it's safer. Wire the 'signal' fron the m-f sw. to fog sw. to relay. Wire pwr from batt. to relay to lights. Done.
MikeH
 
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