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turn signals don't work when headlights on - LEDs

SmudgeServices

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i was originally having the traditional problem of my all my lights dimming at idle, ammeter on discharge. when i drove or accelerated the RPM's, all lights would get brighter through the car inside and out. to help solve this problem i have made several changes...

1. swapped all lights inside and out to LEDs (to increase brightness and reduce power requirement)
2. swapped the hazard and turn signal flashers to true, no-load LED friendly flashers
3. upgrade the alternator to a brand new, 2 wire high output 130 amp (bypassed the ammeter and ran direct 2 gauge power from the starter relay)

all the lights in the car work, and are much brighter than they originally were. the hazards and turn signals work just fine with the car on at idle. my current issue...

1. although steady and bright at idle, all dash and exterior lights do still brighten up when revving up the RPM's. it's certainly better, much less than it was originally but it still happens and is noticeable. (this is less of an issue and more of a symptom)
2. the real issue is that, running or not, when i turn on the running lights the front flasher lights get a little dimmer and the flashing is barely noticeable; definitely not safe for use. when i flip the headlights on all the way the turn signal flashing isn't visible at all. it's like the load/draw from the headlights are preventing the flashers from working properly. the back/taillight flashing works just fine with no noticeable difference when the headlights are on. the problem is only with the front valance turn signal lights.

after reading through so many forums, i'm wondering the best solution...
-- do i need to install a headlight relay kit? they're kinda expensive
-- do i just need to install load resistors on the front turn signals? they do seem to be the only lights dramatically effected, although all dash and exterior lights do still get slightly brighter when the RPM's rev up. the fact that they all do still get slightly brighter with higher RPMs still trips me up considering the new alternator


any ideas or more confident understanding of what to try is greatly appreciated. i'd like to avoid spending money on a fix that doesn't work and just unnecessarily messes up the stock wiring.
thanks!!!
 

NoCar340

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It sounds to me like your car's got grounding issues.

I had a eerily-similar issue to what you're experiencing right now with my Valiant, which had, and still has incandescent bulbs. Faint, short turn signal or hazard flashing, park lamps shutting off when the headlamps were on, etc. A new ground wire from the negative battery terminal to the core support, installed on clean metal with a clean bolt, solved it 100%. Make sure that connection is clean and has a good wire, and double-check the grounds for your park/indicator lamps. They must be clean metal to clean metal with clean bolts, no paint or corrosion in the way.

Your original problem is something similar to what a friend went through 20+ years ago with his '70 Road Runner. New alternator, starter, battery cable, on and on. He ended up replacing every single wire in the car with new Year One harnesses except one, because that one looked almost brand new: the negative battery cable. I showed up just after the new taillamp harness was installed and the dimming problem was better, but still present. I slashed his ground cable with a utility knife, and what appeared to be brand new was solid green corrosion from the battery to the engine. With a new ground cable, the problem was solved.

Never trust the exterior appearance of wiring. Years later, a friend with a Cummins diesel had a similar problem. When his grid heater came on during cold-weather drives, the alternator voltage would drop below 11V. I mentioned the Road Runner, but this guy refused to check that wire because "it's fine... look at it." More green death hiding inside the insulation, far from prying eyes. Same solution, once again after spending a bunch of unnecessary money on a huge alternator and two Optima batteries.

Don't want to slash what might be a good cable? Use a DMM and check resistance between battery (-) and clean metal on/at the cable end. It should be very close to zero. An ohm is too much for a cable that large and that short, assuming the factory battery location.
 

SmudgeServices

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It sounds to me like your car's got grounding issues.

I had a eerily-similar issue to what you're experiencing right now with my Valiant, which had, and still has incandescent bulbs. Faint, short turn signal or hazard flashing, park lamps shutting off when the headlamps were on, etc. A new ground wire from the negative battery terminal to the core support, installed on clean metal with a clean bolt, solved it 100%. Make sure that connection is clean and has a good wire, and double-check the grounds for your park/indicator lamps. They must be clean metal to clean metal with clean bolts, no paint or corrosion in the way.

Your original problem is something similar to what a friend went through 20+ years ago with his '70 Road Runner. New alternator, starter, battery cable, on and on. He ended up replacing every single wire in the car with new Year One harnesses except one, because that one looked almost brand new: the negative battery cable. I showed up just after the new taillamp harness was installed and the dimming problem was better, but still present. I slashed his ground cable with a utility knife, and what appeared to be brand new was solid green corrosion from the battery to the engine. With a new ground cable, the problem was solved.

Never trust the exterior appearance of wiring. Years later, a friend with a Cummins diesel had a similar problem. When his grid heater came on during cold-weather drives, the alternator voltage would drop below 11V. I mentioned the Road Runner, but this guy refused to check that wire because "it's fine... look at it." More green death hiding inside the insulation, far from prying eyes. Same solution, once again after spending a bunch of unnecessary money on a huge alternator and two Optima batteries.

Don't want to slash what might be a good cable? Use a DMM and check resistance between battery (-) and clean metal on/at the cable end. It should be very close to zero. An ohm is too much for a cable that large and that short, assuming the factory battery location.

Thanks!! Simple enough, I'll definitely go check that negative battery cable now. Just blows my mind since all other flashing lights (including the fender markers) are functioning properly. I'm not educated enough to see how this could be possible but I totally trust ya :)

To add more info to the situation, I'm attaching a schematic and picture of the wiring I got going on behind the valance lights.
As shown on the schematic, wiring to the valance running light ("DIR SIGNAL PARKING LT") and fender marker ("FENDER TURN IND") look proper except it also shows a "MARKER LT". It has 3 wires running to it instead of 2 so it seems obvious that this is the yellow plug in my picture. What I don't understand is why this yellow MARKER LT plug isn't being used? Is it supposed to be? Related?

PXL_20210105_223859785.jpg


challenger_1970_wiring_schematic_headlight.jpg
 

SmudgeServices

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So I just played with the ground wire running from the negative battery terminal to the core support. It was an 8 gauge wire that looked pretty clean. Sliced it open anyway and it looked good, no corrosion inside. DMM read .6 ohms from terminal to core support connection.

Considering the alternator upgrade, I figure I replace this wire anyway (worth the $3 to be sure). I swapped it out with a fresh 4 gauge wire and extra cleaned up the metal at the connection. Checked the resistance and it's exactly the same .6 ohms. When I start the car it reads 3.1 ohms.

Onward... Hmmmmmm...
 

NoCar340

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FENDER TURN IND is not the sidemarker lamp. It's the fender-top indicator visible to the occupants of the car (typical of cars with A04 light group, i.e. not all cars have them). MARKER LT is the sidemarker seen by people off to the side of the car. It is not supposed to blink, simply glow whenever the park lamps are powered.

From what I can see on your car, your sidemarker has the wrong lamp socket and wiring and it's connected to the single-pin connector for the A04-style fender-top turn signals. The socket for the sidemarker should have two wires and terminals, which connect to the yellow plug in your photo. If you don't have fender-top indicators, the wire currently powering the sidemarker is just left dangling by the factory. You can do the same... or add fender-top turn signals.

This, however, may not ultimately solve your ground issue. The front park lamp/turn signal assemblies ground through their housings via the valance. There must be a clean electrical path from the valance to ground, either via a wire/strap to the core support or through the various panel contact points and fasteners holding all that bodywork together.

There's a couple of things that could be happening, or a combination of the two:
  • 1) Since the sidemarker is connected wrong, the ground path for that bulb could be weak since the sidemarker lights are not self-grounding like the fender-top indicators are (see diagram).
  • 2) There's not a "clear" path from park lamp/turn signal housings to ground.

Start by simply disconnecting the sidemarker lamps and see if there's an improvement (even if it's not much). Don't reconnect them to their current location, ever. We'll come back to that in a moment.

Make sure the small wire coming from battery (-) has got a clean connection to its mounting point on the body... on my Valiant, that's the core support and that connection was heavily corroded. I cleaned the terminal and its contact point on the core support with a Scotch-Brite wheel, and bead-blasted the bolt. That was all it took on my car, and maybe it will on yours, too. If not, get a couple of jumper wires with alligator clips, or lengths of wire and some small ring terminals about the right size, long enough to reach from the back of the park-lamp mounting bolts directly to the battery. Attach those wires to (-) and try the test again. I've got five American dollars that says they'll work correctly. If they do, you need to figure out a way to clean up your ground path, either with jumper wires/ground straps or cleaning some of the areas where the valance contacts other panels with better grounds. Your ultimate goal here is to get the resistance between the park lamp/turn signal housings and the small ground wire from battery (-) as close to zero as possible. The closer you get, the better they'll work and the longer they'll stay working. There are easy, ugly ways to do it, like jumper wires from the park lamp housings to the core support, and cleaner, less-visible ways like a clip-on or bolt-on ground strap from a valance edge (clip style) or fastener (ring terminal) to the core support. Either would work as long as the connection is clean (no paint or corrosion in the way), but that's your call--it's your car.

If any of this is unclear or you have further questions, ask away. I cannot stress enough the importance of grounds... which reminds me, you do have a ground strap from the engine to the firewall, right? If that's missing or compromised, it could be causing your overall "darkening at stop signs" issue. My Challenger's been apart since before I got it, but on the Valiant it's a simple braided strap that travels from the back of the head to a firewall bolt.
 

NoCar340

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So I just played with the ground wire running from the negative battery terminal to the core support. It was an 8 gauge wire that looked pretty clean. Sliced it open anyway and it looked good, no corrosion inside. DMM read .6 ohms from terminal to core support connection.

Considering the alternator upgrade, I figure I replace this wire anyway (worth the $3 to be sure). I swapped it out with a fresh 4 gauge wire and extra cleaned up the metal at the connection. Checked the resistance and it's exactly the same .6 ohms. When I start the car it reads 3.1 ohms.

Onward... Hmmmmmm...
OK, so your cabling is good (you responded just as I was finalizing the above). That eliminates one issue, now on to the next as described above.

In terms of your sidemarker fiasco, you can quickly butcher together functional harnesses using generic two-wire sockets that fit the housings (pretty sure Standard Motor Products makes them...HP4630 maybe?) and a Hopkins 47965 two-pole extension that will plug into your sidemarker connectors (also available from Curt, their number is 58020). All are basic parts-store stuff; I know I stock 'em. You only need one of the Hopkins/Curt part since it's an extension--it comes with two of the needed plugs. Restoration correct? Absolutely not, but you can use that getup while you look for factory-style replacements... or just live with 'em if you're not dealing with a show car.
 

sixpactogo

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I think you need to swap your signal light to the yellow plug. The plug you are using now I believe goes to the turn signal light at the top of the fender. (if used)
 

SmudgeServices

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unplugged the side fender markers. hit 3 parts stores and none had the plug/pigtail i need. the socket itself is a single wire also... gonna go ahead and order the right ones soon so i can have 2 wire and properly plug into the yellow plug of the harness. for now, the side fender markers are simply unplugged.

i ran an alligator clip from the housing of the left parking light directly to the battery negative. ran another one from the right parking light housing to a solid ground in the engine compartment (wasn't long enough to go directly to the batter). i didn't start the car but simply tested again with the key in the 'on' position and saw zero change. behaving just the same as before: all exterior lights work as expected until the headlights are on running or fully on, then the front parking lights won't blink.

i do have a 4 gauge ground wire running from the batter negative to the engine (exhaust manifold bolt) and a new, shiny braided ground from on the backside of the engine to the firewall. i'll unbolt to verify their integrity but they look like solid clean grounds from my quick gander. could there be another standard ground i should check on? maybe one inside? the dash lights do the 'brightening' when revving and the dimmer for those dash lights doesn't really work: it only works when turned all the way counter-clockwise (down?) and turning it clockwise any amount turns off those dash lights. seeing talk about grounds for that dimmer on other forums.... possibly related or a cause? i'm really in the weeds with my ideas now, sorry. the direct ground to the battery from those parking light housings seemed to make the most sense.
 

SmudgeServices

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okee dokee, i think i got the issue worked out so i'm posting back in case anyone comes across the discussion in the future.

first thing i did was order the correct 2 wire pigtails for the fender side markers as instructed above. many websites claimed had them available but they all showed the same, wrong ones so be careful and don't trust rock auto for this one. ugh! sure enough though, "Herb had 'em!" and they were affordable. they came and i installed them to ensure a complete circuit. (although, they didn't come with the push in clips so they could attach to the housing so i had to rig them in. see pic. if anyone knows where i can purchase the proper push in clips please let me know!).

i cleaned all my grounds related to the turn signal lights until i was 100% confident in them. i tested the voltage at the sockets and it was a good 12.4v using the ground. i followed the wiring all the way back through the system, inside the car to the flashed testing voltage to find the issue. hind sight is 20/20 and i feel so foolish, but the major source of the problem was right there in front of me the whole time.
the negative wire coming off the back of the passenger turn signal light, before even it plugs into the harness, had electrical tape on it (actually can be seen in the photo i posted above). i didn't think twice about it but in being thorough i unwrapped it just to see what was underneath. sure enough, that negative wire was busted and hanging together by a thread. i cut it and wired it back together clean, complete, and solid. since that black wire is shared with the other turn signal light i knew that was it. right away the lights were working but the one side was dimmer, and less performing that the other. i looked at the LED close up and could see that a few of the diodes were out. i ordered brand new LEDs for both, installed, and viola it's all good now.

in summary---
1. fixed broken negative wire off the back of the passenger turn signal
2. replaced the LEDs/bulbs
3. installed the proper 2 wire plug/harness pigtail for the fender side markers

thanks for all your in depth knowledge and taking the time to share it so thoroughly @NoCar340 , much appreciated

PXL_20210117_211559644.jpg
 
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