I just removed the stock radio from my 2018 SL. I have a Pioneer aftermarket ready for install. I removed all the wire harnesses from the radio leaving me a clean slate. I have also purchased the power harness from slingtunes.com https://slingtunes.com/shop?olsPage=products%2Fspss18 The power harness has 3 wires red,yellow and black. I don't see any harness on the sling that I just removed from the stock radio that also has the 3 wires like the purchased power harness. I see a harness that might fit but it has 5 wires. Also, the aftermarket Pioneer has all the color coded speaker wires but where are the speaker wires in the sling and are they color coded the same. Most or let's say every video on Youtube are on Slingshots before 2018 and none really explain how to hook up the power harness or even the speaker wires. Anybody that has any knowledge please contact me via email and I'll give my number so we can talk in person instead. Need help bad on this one. Thank you. frehleycomet1@yahoo.com 
2018 Aftermarket radio install...
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That 3 wire harness: The loose wires connect to your stereo for power. Then down in the cubby hole under the stereo, you'll find the other connector mate with 5 wires to give you power to your stereo (Positive, Ground & ignition). You don't use 2 of the wires from the SS connector.
You can use the stock speaker wires if you're not running an amp - they are inside that big 32 pin connector there in the back. There's a post on here somewhere with the wiring diagram to tell you what pins to pull. Otherwise, you can run your own speaker wires or amp RCA from the back of the stereo.
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if you can't find the harness he speaks of, it has a tendency to fall between the frame and tunnel cover when they are installing. I found my by accident when looking from below, up past the transmission.
