I've been searching this issue for the last 2 days and I can't seem to find a solution or anyone having the same issue.

My car is a 98 Formula and I'm having an issue where the driver's side DRL is always on but very dim. I listed everything I've changed or checked below while trying to diagnose this problem.

- All exterior bulbs have been changed to LED, except the 3rd brake light. All lights are working.
- Both turn signal and hazard flashers changed to Keep It Clean 10853 No Load flashers.
- Car is running on a Holley Dominator ECU, factory PCM is removed and currently do not have the factory gauges working. Not sure if this could be the cause or not.
- I confirmed all fuses in the IP fuse block are good.

When I key the car on both DRL lights come on bright, then driver's side will go dim. I checked power at the DRL module and the RH turn signal wire has 12v, activate the RH turn signal and it flashes going from 12v to 6v, this seems normal. When I check the LH turn signal wire, it only has 6v, activate the LH turn signal and it flashes going from 6v to 4v. Even when the key is off, the LH turn signal output wire still has 6v and the light stays on but dim.
I put in a spare DRL module that I have and still have the same issue. Since I had an extra module, I did the DRL bypass mod by soldering the A & B circuits of the C2 connector. Keyed the car on and confirmed the RH DRL is now off....but the LH DRL is still on and dim.

Anyone have any ideas what could be causing this? I've run out of things to check or try. None of the searches on here or any FB groups seem to be having the same issue as I am. Any help would be appreciated!

 

i had a similar problem on my 02 trans am. the passenger side drl would be off or dim. i replaced the bulbs and put some bulb grease and it would work for a day or two and then the problem would come back. i ordered new bulb housings/sockets from mouser electronics because they were pretty brittle from 20+ years. i put the new ones in and led bulbs and they work great now. do a search on here for the part numbers. im not sure if the housings/sockets are the same for a 98 formula. hope this helps.

 

I replaced both DRL sockets already, sorry I forgot to mention that in my initial post. The LH bulb doesn't lock in as tight as the RH side, so I'll replace the socket with another spare one that I have. I'll post back if that solves the problem or not.

 

Your meter readings are quite odd. The factory system does not vary voltage to the turn signals, DRLs, or parking lights. They are always 12V or 0V depending on usage. There are two filaments in the factory incandescent bulbs - one bright for signals and DRL; and the other dim for parking lights. Those two filaments run from separate wires... blue (light blue on left and dark blue on right) for the bright filament and brown for the dim filament. LED bulbs don't have filaments, but they simulate the function internally, displaying bright when power is on the blue wire and dim when power is on the brown wire. When using the turn signal without lights on, the blue wire will alternate between 12V and 0V to flash the bulb between bright and off. When using signals with the headlights on, the blue wire still cycles between 12V and 0V, but the brown wire also has 12V so they flash between bright and dim (i.e. between blue and brown wire power).

How are you measuring the voltage? You should measure at the unplugged lamp socket between the blue wire contact and a good chassis ground. You should get 12V or 0V depending on whether the DRLs are active or the turn signal is active. Assuming that you get those readings, then try measuring between the blue wire and the black wire (ground) in socket. If you now get different voltage readings then you have a bad ground on that side. The front lamp ground is a bolt on the upper radiator support on each side.

Another possible cause is if you installed 3156 (single filament) LED bulbs rather than 3157 (dual filament) LED bulbs in one or both of the front lamps. They look identical, so it is possible, but usually that would cause additional side effects. Still, it can't hurt to check... pull out the LED bulb and replace it with the original incandescent bulb to see if the problem goes away. That will confirm whether the problem is wiring related or bad bulbs.

 

check your grounds

 

I went out to check some things on my lunch break. First, I removed the led bulbs from the front DRL sockets and put in some 3057 bulbs that I had laying around. I noticed that all my rear taillights got much brighter and same with the rear turn signals while flashing. So I think something was not right with the led bulbs I had in the DRL sockets. Unfortunately, this did not solve my issue.

I went ahead and checked my grounds as well, since they are moved slightly from the stock frame location. My battery is moved to the back of the car so I checked the resistance from my battery post to both the left and right ground locations up front, this showed a 0.1 ohm delta. I also checked from my front ground locations to each ground terminal in the DRL socket and both show 0-0.1 ohm. I assume this means my grounds are good.

With the key on, parking brake off and light switch off, the light blue wire voltage at the socket is 10v. Key off, the light blue wire, the voltage is still 10v.

This is what I noticed now that I have the 3057 bulb in it and both bulbs out of the housing. When I first key the car on, both RH and LH DRL bulb (lower filaments) are on and bright. After a couple seconds, the LH lower filament goes very very dim and starts flashing on/off. When I turn the LH turn signal on, I can see both filaments are lit and the lower filament is bright (looks exactly same as RH with RH turn signal on). Turn the parking lights on and the LH top filament goes on but not as bright as the RH side and the LH lower filament is dimly flashing like with just the DRL is on.

Sorry for the long post and I hope it's not confusing. I'm just trying give all the details I can. After a couple days trying to diagnose this, I'm starting to pull my hair out lol

 

Have you done any other wiring changes besides relocating the battery? With the key on and parking brake disengaged (i.e. when the DRLs would be on), you should get full battery voltage at the blue wires in the front sockets - that would be about 13.5 volts or greater depending on your alternator with the engine running or about 12V with the engine not running. 10V would be too low unless you have a bad battery or there's some excess resistance in the circuit. With the key off, regardless of the parking brake, you should get zero volts on the blue wires - neither the DRLs nor the turn signals will operate without the ignition being on.

Let's work on getting that part working as it should before we move on to the other symptoms you describe... I suspect they're related and solving the first issue might solve the rest as well.

 

The fuse block has been relocated to underneath from where the stock location is, in order to make room for a turbo but nothing was changed on the wiring for that. Also stock wiring has been re-routed a bit since the lower core support has been changed for radiator placement. I don't think anything has been altered on the headlight harness from the firewall but I would have to pull all the loom off to confirm. I was hoping there was a more obvious fix before going through the trouble of checking all the wires in the headlight harness l, but if it has to be done, then it has to be done. Also there is no stock PCM in the car and the factory gauges are not hooked up. I did confirm the DRL sockets are pinned correctly, brown wire in cavity B, ground wire in cavity G and light blue and dark blue terminals are in cavity A in the sockets.

Battery is a new yellow top Optima, the voltage is a little under 12.0v because I've been messing around trying to diagnose this issue. But I just confirmed again, key off, the light blue wire in the DRL socket has 10.1v. But when you first key the car on, that light blue wire gets full battery voltage for like 4 seconds, then it drops to 10.1v and the filament starts flashing. So I don't think it's a case of high resistance because it's getting the full battery voltage at key up, then it drops. Something seems to be back feeding that light blue wire circuit with 10v. I'm not sure how that can happen though.

I did just notice something that I hadn't noticed before. After the 4 seconds or so when the LH DRL light blue wire drops to 10.1v, the LH turn relay in the DRL module starts clicking. This explains why the filament is flashing. When I turn the LH turn signal on, the DRL stops clicking and the turn signal flasher starts clicking. When I turn the turn signal off, the DRL relay starts clicking again. The DRL relay also continues clicking when the RH turn signal is on as well. I'm really at a loss to what is giving the DRL module LH turn relay signal to flash. I don't have the wiring knowledge to be able to trace the wiring schematics, in order to figure this out.

I also seriously doubt that I have 2 DRL modules that have the same issue, so something else has to be causing this.

 

I've been pouring over the schematics trying to determine how you could possibly get power on the blue wire with the ignition off. The only thing I can think of is a problem with your soldered DRL bypass. It's the only thing that is out of the ordinary for that circuit. That is not the best way to bypass DRLs because of the potential for error and the difficulty of reversal should it become necessary or desirable in the future.

If you really don't want DRLs (personally I feel that they are an important safety item) then you can still do a bypass that should hopefully also bypass any issues caused by the soldering. What you would do is remove (or cut - but removal allows later reversal) the four blue wires in the black 8-pin connector at the DRL module, then connect the corresponding plain and white stripe wires together (i.e. light blue to light blue/white and dark blue to dark blue/white). This will completely bypass all DRL function while retaining normal turn signals.

 

Just some perspective on the DRL disable method used here (soldering a jumper between those two terminals) - this will result in no issues at all if done correctly. I've done this on many LS1 F-bodies, including all the ones I have owned (I am not a fan of DRLs), and never had any ill side-effects such as the above or otherwise. In fact, it's been this way on my current '98 Z28 for over 20 years without a problem. I do agree though, that if something has been done incorrectly here it could lead to various issues but, in this case, it sounds like the OP had the same problems with a previous DRL module which didn't have any soldering changes made...and if I'm correct in that understanding then I doubt the soldering job is at fault here.

 

I don't disagree - the solder method works when done without error. However, there's always the possibility that something could go wrong... solder overflow to adjoining circuits, cold solder joints breaking, existing board traces getting broken, etc. Plus the bypass is completely hidden, making it a diagnostic nightmare for someone else in the future. The external wiring cross connection requires no skills other than crimping wires and is completely obvious to anyone (future owner) later trying to figure out why their DRLs aren't working.

In this case, I'm just using the diagnostic axiom of whatever was changed before the problem occurred is the first place to look. Frankly, if it's not the DRL module and none of the other related wiring has been touched then I'm at a complete loss as to how power could be getting to the front lamps with the ignition turned off. The only non-ignition power would be the parking lights but they power the brown wire at the sockets not the blue wire.

 

I completely agree with this, and I would always recommend the same. But my concern here is this:

Unless I'm misunderstanding the above, it reads as though the problem already existed before the spare DRL module (with the soldering mod) was installed, meaning that the issue didn't change at all as a result of the mod nor the "new" module. If that's the case, I think it'd be a waste of time to chase this as a potential cause. But, otherwise, I would certainly agree with your line of thinking.

 

Well, the only other thing I can think of is that somehow there's a short (cross connection) between the front lamp wiring and some power source. It's easy enough to check... unplug the black connector from the DRL module and then check if there is any power on the light blue wire. Since it should be nothing more than a straight run directly to the socket, there should be no power there. If there is, remove the bulb and check again in case you're getting back feed through the bulb from something else like the parking light circuit. If you still see power then it may be a case of tracing the wire to find where it's cross connecting to another circuit.

If you don't see power at the connector when it's unplugged then check the DRL module pin - either directly with a meter probe or by plugging the connector back in and probing from the back side of the light blue wire. Now if you see power then it can only be that the DRL module is the source and is faulty.

 

Maybe there's a short/low connection between the lamp wiring source..

 

Thanks for all the ideas! I'll check all this today and let you know.

I have 2 DRL modules, one that is soldered and one that is stock. I currently have the unmodified one in the car. When I put the modified module in, the only thing that changed was the RH DRL light was off..the LH one was still flashing dim.

 

So today I confirmed voltage at the battery just to make sure, 11.65v. Unplugged the DRL module completely with key off and checked all pins for power, parking brake was off. Then I checked all pins for power with key on, parking brake off.

i put it all in excel so it would be easier to visualize. I'll attach a screenshot of the results below. I highlighted where the problem seems to be coming from.

Maybe this will help narrow down the problem. Let me know what you think.

 

I traced down the TAN/WHT wire (DRL module blue connector pin D) to the brake malfunction indicator lamp driver module behind the HVAC control panel. Checked for power and found 10.6v there. When I removed the instrument cluster from the car, this TAN/WHT wire lost the 10.6v. So it looks like something in the cluster connector is feeding 10.6v to the TAN/WHT wire and then to the DRL module.

Upon doing this, I remembered that 20yrs ago, this 98 harness was converted to 99+ to use the 0411 PCM. So there are wires behind the cluster tied together in order to run the 99+ cluster. I need to go through the schematics to see what circuits are tied together and hope that this is the root of my issue. I also forgot to mention in my previous posts that the ABS module has also been removed for the car. This could also be part of the reason for the TAN/WHT wire is getting 10.6v, when it shouldn't be.

Sorry for sending you guys on a wild goose chase, apparently the wiring modifications I forgot about may be the root cause of my problem. I'll keep looking through the cluster schematics to see if I can figure this out.