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The fog lights on my 88' don't go out when the highs are on they can be used in conjunction or separately from both the high or low beams, they even go on when just the parking lights are on and the headlights are down. I'm guessing the 90-96 cars operate differently.
It seems based on this thread that the issue the 1990-1996 guys are having is that turning the fog lights on also activates the high beams, which is not ideal since high beams make it harder to see in fog (in my experience).
As far as the grounding issue I'll have to refer that to someone with more electrical knowledge.
I have noticed it mentioned that the pre-90' cars are wired differently.
Anyone know if LED headlights will work in those cars without needing to re-wire or if not what has to be done to get everything working in a pre 90' car?
My '86 has the fog lights grounded directly. I didn't need to modify my wiring.
I suspect any changes would have happened in 1990, when everything was modified.
My '86 has the fog lights grounded directly. I didn't need to modify my wiring.
I suspect any changes would have happened in 1990, when everything was modified.
Hmm, that is good news for me, I too suspect the wiring in my 88' is the same as your 86'. From what others have said the newer cars cannot have fog + high beams going at the same time and my C4 can which seems to suggest it is grounded directly like your 86'
im having the same problem. i plan on doing the fog light relay ground fix on my 91.
im having another weird issue. when i turn my fog lights on(they wont work now) and shut off the switch the headlight motors run for about five second even though the headlights were never up.
Hi Circuit Doctor!
I have the same problem with my aftermarket headlights. The high
beams and fog lights switching are all messed up. I read your thread back in 2015 and it made sense,
so I purchased all the components. I just now (Memorial Day weekend) got around to doing the job.
I disassembled the driver's side head light assembly and found this wiring.
I realize this is HID, not LED. Will this fix still work? Which wires
to splice so the bulb can add resistance?
Thanks!
Ted
P.S. I wonder if in my case it would be easier/better to just ground
the fog lights separately.
Last edited by 95ZR1; May 29, 2017 at 07:00 PM.
Reason: Wanted 2
I was thinking about it over a Memorial Day drink
and realized that the "U" shaped 3-wire connector
must still be somewhere running back to the cabin
so I dug deeper behind the headlight and found it.
So same question: will splicing the two wires and
adding a bulb do the trick? Thanks again!
I know this is an old thread, but reading through it got me wondering if you could use a changeover relay, triggered with the high beam voltage, to control the ground circuit. IE, when not energized, the fog lights would be grounded through the relay's 87a circuit. When energized, the ground would then switch to 87, causing the fog light circuit to become open and the high beam circuit to close.
If this would work, it would eliminate the need for the bulb hack, but you would have to route the grounds appropriately (perhaps too complex).
Am I overlooking something fundamental?
Keith
Last edited by Keith Huffstutler; Sep 20, 2017 at 01:04 AM.
Hi Guys!
I just picked up a beautiful 1996 LT4 Collector Edition over the weekend. What an awesome car! That LT4 just pulls hard throughout the entire RPM range.
As C4 owners are certainly aware, the headlights are very lacking. I decided I wanted to purchase the GE Nighthawk LED headlights for the car. I installed them, and I am blown away by their performance. However, like everyone else who bought them, my foglights no longer function properly and cause the high beams to switch on.
Since my background is in electrical engineering, I reviewed the schematic of the headlight system and observed the foglight relay's coil gets its ground through the high beam filament. The purpose of this is to disable the foglights while the high beams are on. Due to the higher impedance nature as well as internal circuitry of the LED headlight assemblies, the foglight relay's coil is acting as a psuedo pull up resistor for the high beam input terminal, thus illuminating the high beams when hitting the foglight switch. In fact, if you were to open your hood and switch on the parking and foglights only, you'd see the high beams flicker lightly as a result of this. The solution is to disable the high beam feed to the relay's coil, and ground the relay's coil directly, or provide a low resistance path to ground for the relay's coil.
Anyway...I'm going to put together a write-up with detailed pictures to outline this when I'm not stuck working 7 days a week. The beauty of my plan is that you will not need to hack any of the factory wiring, and add one jumper wire. Would you guys be interested in this?
Before performing this procedure, please be aware of the following:
You are performing this procedure at your own risk. I am not in any way liable, either express or implied, for any damages caused by this procedure, either deliberate, accidental, incidental, or circumstantial including, but not limited to; damage to vehicle, injury, fire, death, invasion by aliens, or snide remarks from friends. If performing this procedure, having basic electrical knowledge is a plus, as is good hand-eye coordination. The steps outlined below using the tools and materials below will ensure optimum performance and reliability and has been tested with successful results; by deviating, you may be unknowingly compromising the aforementioned parameters. It's a good idea to disconnect the battery before starting this.
Tools:
- #2 screwdriver with tip in good condition
- Wire cutters/strippers
- Soldering iron (optional)
- 7mm socket and socket handle (recommend 1/4" drive) or 7mm nutdriver
- Pencil
- Xacto knife
STEP 1:
Raise the hood and rotate the headlight manual adjustment **** until the light is positioned like this. Remove the two Phillips head screws fastening the shroud. Make sure the screwdriver is like new, these screws will strip out very easily with a worn tip!
(Note: You can install this modification on the driver or passenger side, it doesn't matter. I installed on the driver side)
STEP 2:
Remove the remaining two 7mm bolts fastening the shroud, and remove the shroud as well.
STEP 3:
With the shroud removed, remove the four Phillips head screws holding the headlight retaining ring ONLY. Do not touch any other screws, or the alignment of the headlight capsule will be altered! Then remove the headlight and unplug the electrical connector.
STEP 4:
A) With the headlight now removed from the vehicle (or out of the box if you're installing the new light for the first time), look at the connector attached to the light. Orient the connector so the 3 pins create the letter "U"; it will look like there are pins at the "East", "South", and "West" locations, and there will be no pin at the "North" location. What will needs to be done is expose and splice into the wires which connect to the "East" and "West" pins. This H4 pinout diagram should help clarify (this is shown as if the male pins face the observer):
On my GE light, these wires were red and white.
B) Using the xacto knife, carefully, and GENTLY cut the insulation around the entire diameter of the wire in two locations about 1/4" apart from each other. Then, join the cuts together, creating an "H" shape. Repeat this on the wire facing opposite the one that was just stripped. NOTE: Be very careful doing this, when the blade feels like it has hit metal (you'll know), don't cut any farther. Avoid cutting into any of the wire strands.
C) Once the insulation has been cut off the two wires, peel the insulation off to expose the copper strands. Using the pencil, "part" the strands in half.
STEP 5:
A) Prepare the #168 socket by shortening the wires to approximately 2" long each. Any additional length is unnecessary. Next, strip approximately 1/2" of insulation off each wire of the #168 socket.
B) Wrap each wire from the #168 socket through the middle of the strands, so it looks like this.
C) (Optional, but highly recommended) Gently push the strands all back together and solder the #168 socket wires to the headlight wires. I highly recommend the use of solder flux in order to achieve the best solder joint possible; this is recommended because these connections will be subject to frequent shock and vibration. At this point, the splices are finished.
D) Wrap each wire with electrical tape.
STEP 6:
Tuck the wiring back into the split loom tubing, and fasten the socket to the tubing with two wire ties, like in this photo. Don't forget to install the 168 bulb into the socket!
From here, the reassembly is the reverse of the removal steps.
Once all this is finished, your foglights and highbeams will function as originally intended!
Here's a technical explanation for those interested:
Starting on the top of page "8A-100-1", and ending on page "8A-100-0" (Current path is highlighted in yellow, and the arrows indicate current flow direction). The current into the relay coil originates at the headlight switch, then travels through the foglight switch when desired. The current then travels through the coil of the relay, into node "A" and onto page 8A-100-0. From node "A", the current travels into "S208", into the high beam filament, and finally returns to ground. Since the resistance of the new LED headlights' high beam input is so high, there is not enough current flow through the relay coil to pull it hard to ground, thus rendering it inoperative. Additionally, the new LED highlights' high beam wire can act as a control signal which simply "tells" the high beam to turn on - the coil of the relay provides this current path from the battery since it has a relatively low resistance in contrast to the high resistance of the high beam input.
The solution is to:
A) Provide a low resistance from the relay coil to ground by wiring a #168 lamp in parallel with the high beam wire into the new LED headlight to ground. This, in turn, will restore the original functionality. This also will pull the voltage of node "A" much closer to ground potential, which will no longer cause the high beams to switch on when the foglight switch is turned on.
-or-
B) Disconnect the "ground" side of the foglight relay's coil from S208, and ground it directly to chassis.
Ok so I have a dumb question. If you have led headlights, you will not be able to have the headlights and fogs on at the same time? At least on un modified wiring?
In my case with my 1996 with Truk-Lite LED headlights, turning on the fog lights would also activate the high beams. Clicking the turn signal stalk would not produce low beams if the fogs were on, it was stuck on high beams. Turning off the fogs, the headlights would work perfectly normally. Circuit Doctor's fix works perfectly for mine, everything now works normally.
Ok so I have a dumb question. If you have led headlights, you will not be able to have the headlights and fogs on at the same time? At least on un modified wiring?
Depends on the brand. Mine were plug and play.
One year later all my forward lighting still works in all combinations.
Ok so I have a dumb question. If you have led headlights, you will not be able to have the headlights and fogs on at the same time? At least on un modified wiring?
The fogs will not work period if you don't do a resistor, circuit doctor method, or the relay mod under the dash. If you do one of those mods, it works just as it did from the factory.
Happy to post images of any forward lighting combination you are interested in.
BTW, did you manage to sell the A4 and get the M6 you wanted?
Yeah I sold it September 15th. Should be buying the M6 car soon. Few cars I am interested in at the moment.
Originally Posted by TorchTarga94
The fogs will not work period if you don't do a resistor, circuit doctor method, or the relay mod under the dash. If you do one of those mods, it works just as it did from the factory.
Does anyone know if you have to do the Circuit Doctor method or the relay mod under the dash with the JW Speaker 8900 LED's for my 94 C4?
If the LED causes a problem, I suppose you can address it at that point. An easier alternative would be probably to use the gizmo that increases the load to the point that it won't cause that issue especially if it is PnP and right behind the bulb.
Tried this mod. Without The Mod, Fog lights turn off with brights and high beam dash indicator stays on weather high beams or low beams are on, but only when the fog lights are activated. With this mod it fixed the high bean indicator abut the fog lights still turn off. The 168 bulb light turns on when i turn on high beams but the fog lights still turn off. Any Ideas? 95 corvette.
Tried this mod. Without The Mod, Fog lights turn off with brights and high beam dash indicator stays on weather high beams or low beams are on, but only when the fog lights are activated. With this mod it fixed the high bean indicator abut the fog lights still turn off. The 168 bulb light turns on when i turn on high beams but the fog lights still turn off. Any Ideas?
What an awesome car! That LT4 just pulls hard throughout the entire RPM range.
