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Discussion Starter · #1 ·
Hi All,

Looking for a bit of advice here. When I turn on my fog lights my RHS (passenger) high beam comes on. The driver's side light is not effected.
High beams turn on/off normally when the fog-lights are not on.

I should also note that the fog-light rewire has NOT been done on my car.

Any thoughts?

Thanks!
 

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Discussion Starter · #2 ·
Alright, an update:

I’ve installed LED headlight and fog lights along with polarity inverters for the headlights. Headlights (high and low) function fine.
The problem occurs when I turn on the fog lights.

When the car is running the fog lights cause the headlight high beams to come on.

When the car is not running, only the passenger high beam comes on.

Any ideas are much appreciated
 

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1988 Supra, NA, Auto, 116K Miles
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Probably a grounding/current issue. A few other members here have suggested these. I bought a pair along with the polarity inverters, but have yet to test them out.
 
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90T
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Its completely normal and due to the crazy way the fogs are tied into the headlights. With regular halogen bulbs the high beam filament is used to power the fog relay so that the fogs only come on with the low beams. What this means is that a little current flows through the high beam filament when the fogs are on, but too little normally to turn the halogens on brightly.

Because LEDs need so little current to turn on compared to halogens, this trick doesn't work anymore and there is enough current in the relay coil to turn on the high beams. The fix is to do the fog mod.

Map Rectangle Line Font Slope
 

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Discussion Starter · #5 ·
Thanks! That’s good to know, it looks like you’re recommending running a wire to the ground from the RB colored wire before it splits off to both the left and right headlights, correct? Does the H and L annotated here signify anything of importance?

I was studying this to diagnose: MK3 TEWD On-Line
 

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Discussion Starter · #6 ·
Perhaps related, or not, it would seem my headlight retractor integration relay is on the Fritz or the headlight motor relays themselves.
After a good many tests and aiming of the lights, the passenger side decided that it won’t open more than half way and refuses to retract unless rotated to the closed position manually.

I’m thinking I have a bad ground and will have to start tracing. The motor itself was getting hot to the touch which was unsettling.
 

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Discussion Starter · #7 ·
Probably a grounding/current issue. A few other members here have suggested these. I bought a pair along with the polarity inverters, but have yet to test them out.
I read through that thread and thought that was to fix the high beam indicator light in the dash, I’ll take a look in more detail though. Only skimmed
 

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Thanks! That’s good to know, it looks like you’re recommending running a wire to the ground from the RB colored wire before it splits off to both the left and right headlights, correct?
No, I was just showing the path of the current that causes the LED lights to come on all the time with the stock setup.

To fix this you need to do the fog light mod. Here is one write up on it, but there's lots of videos about it on you tube.

 

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Discussion Starter · #10 ·
Thank you! I’ll figure out the headlight motor retraction issue first and then work on the fog light mod.
 

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Discussion Starter · #11 ·
Speculation here: could the same issue with fog and high beams be the culprit for the headlight motor operation?

It feels entirely too coincidental for it to be unrelated, but I definitely don’t want to further modify and add complexity if it’s not related.
 
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