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Classic Cars & RestorationQuestionCommunity Starter

2018 Kia Optima — old 6V-to-12V conversion has decades of splices

V8CollectorCommunity StarterDec 18, 20252018 Kia Optima EXChicago
2018 Kia Optima EX, about 143,500 miles. I bought a classic that was converted years ago and several owners have added wiring since. Everything works now, but the harness is messy. At what point is a fresh harness safer than repairing sections forever? I am trying to get the facts straight before spending money. What would you check next?
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6 replies

CanyonScout481Community StarterCommunity StarterDec 18, 2025permalink
I'd treat 12V warnings as a no-ignore. On the 2018 Kia Optima, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. Then you'll know the next fork. On “old 6v-to-12v conversion has decades of splices,” that was the fork that mattered for me. Write the result down so the next test isn't a repeat of the last one. No warning lights, which is why I'm documenting it.
WeekendWrench782Community StarterCommunity StarterDec 19, 2025permalink
Low-voltage gremlins will strand you even with a full pack. Try a second charger before blaming the 2018 Kia Optima — site sharing and pack temp change the curve a lot. I'd do that before spending real money. Any freeze-frame data saved? If this is nothing, great. I want that in data.
CanyonScout481Community StarterCommunity StarterDec 20, 2025permalink
Fair point. Counterpoint: Match starting SOC and battery temp if you're comparing 2018 Kia Optima charge sessions. Then you'll know the next fork. Time, temperature, and whether it's in gear are the notes that actually help a shop. A day of patience here is cheaper than a wrong part. Wrote this up on my lunch break.
TireBuilder162Community StarterCommunity StarterDec 19, 2025permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2018 Kia Optima so service can see what you saw. Then you'll know the next fork. Run the total, not the monthly, before you commit. This is me being the wet blanket on purpose.
NewCarDetailer44Community StarterCommunity StarterDec 19, 2025permalink
Fair point. Counterpoint: Match starting SOC and battery temp if you're comparing 2018 Kia Optima charge sessions. Then you'll know the next fork. This is from a 2018 Kia Optima in Chicago with 143,500 miles. That's the whole play. Doing the boring step first on purpose.
HybridHauler726Community StarterCommunity StarterDec 19, 2025permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2018 Kia Optima so service can see what you saw. Then you'll know the next fork. That's the whole play. I'm keeping receipts and dates in one folder.
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