15-17 headlights on 18+

[isacchernandez12]

Hey guys,
I’m running into an issue. I’ve got a 2020 Mustang GT and did the I-5 ultimate GT500 front end conversion (essentially an OEM spec gt500 front end). The problem is I had to use 15-17 headlights which are HID on my LED 18+ harness. When it comes to pin out they’re nearly identical except for 2 extra pins on 15-17 headlights. But those don’t show they’re used for power or ground so they shouldn’t matter.
I know it’s possible due to finding a forum on here of a guy that had a 19 and did the OEM GT350 front end conversion and figured out how to get it to work. But when asked how unfortunately he didn’t respond.
I’ve been banging my head trying to get this to work I don’t want to go LED aftermarket since these headlights are full RGB.
So any help would be appreciated!

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[Joe Gonsalves]

The HID lights use a ballast resistor. Maybe that is what the extra 2 pins are for.

 

[Msteele]

2020 headlight wiring harnesses differ from 2015-2017 versions primarily due to the shift towards LED technology and updated connector pinouts, particularly in WRX/STI models. While 2015-2017 models typically use halogen/halogen-compatible systems, 2018-2020 models require specialized adapter harnesses to handle LED C-lights and integrated turn signals.
Subispeed +2
Key Differences and Compatibility

• Connector Types: The 2015–2017 harnesses use a different connector configuration than the 2018–2020 models, requiring conversion adapters (e.g., from Subispeed or olm.com) to make 2018–2020 LED lights functional on older models.
• Functionality: The 2015–2017 systems are generally designed for basic halogen setups. In contrast, 2018–2020 models often include built-in LED turn signals, requiring additional two-pin connectors in the harness for integration.
• Wiring Upgrades: When upgrading to newer, higher-intensity LEDs, some users may require a 12- or 14-gauge wire harness to support the increased electrical load.

 

[Msteele]

Also, there is this: https://olm.com/products/olm-15-17-...you to install 2018-2020 OEM,WRX Base / Premi...

Beautiful car by the way!

 

[isacchernandez12]

Also, there is this: https://olm.com/products/olm-15-17-headlight-upgrade-harness-for-18-headlights-pair-2015-2017-wrx-sti#:~:text=Current price $59.00-,OLM 2015-2017 WRX / STi Headlight Upgrade Harness,for 18+ Headlights (Pair)&text=in stock-,These harnesses will allow you to install 2018-2020 OEM,WRX Base / Premi...

Beautiful car by the way!

Too bad it’s for a Subie and not Mustang. That would of been perfect

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