Classic Cars & RestorationDiscussionCommunity Starter

2024 Mazda MX-5 Miata Club — anyone else: Old car was converted to 12V years ago — wiring is a mess

PixelMom42Community StarterAug 4, 20262024 Mazda MX-5 Miata ClubChicago
2024 Mazda MX-5 Miata Club, about 118,000 miles. Picked up a classic that was converted from 6V to 12V by several previous owners. It works, but the harness has splices everywhere. Would you repair sections or start over with a modern fuse panel and new harness? I'm in Chicago. Appreciate any ideas on what to check first.
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11 replies

TireRider24Community StarterCommunity StarterAug 4, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2024 Mazda MX-5 Miata, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. Then you'll know the next fork. On “5 miata club — anyone else: old,” that was the fork that mattered for me. Time, temperature, and whether it's in gear are the notes that actually help a shop. I refuse to clear codes until someone else sees them.
TireRider24Community StarterCommunity StarterAug 5, 2026permalink
I hear you, though I'd still want a second check. Leave the alerts on the 2024 Mazda MX-5 Miata so service can see what you saw. That's where I'd start. Keep sale price, fees, and rate as three different conversations. If it repeats twice more I'll book time.
TowFanCommunity StarterCommunity StarterAug 4, 2026permalink
Low-voltage gremlins will strand you even with a full pack. Try a second charger before blaming the 2024 Mazda MX-5 Miata — site sharing and pack temp change the curve a lot. I'd do that before spending real money. Run the total, not the monthly, before you commit. I've seen both outcomes, which is why I'd test instead of assume. Trying not to diagnose from the couch.
TowFanCommunity StarterCommunity StarterAug 4, 2026permalink
Don't clear the alert just to make the screen pretty. Leave the alerts on the 2024 Mazda MX-5 Miata so service can see what you saw. That's where I'd start. Run the total, not the monthly, before you commit. I'd rather be boring and correct. That's my plan before I call anyone.
TrackDad34Community StarterCommunity StarterAug 5, 2026permalink
I'd treat 12V warnings as a no-ignore. On the 2024 Mazda MX-5 Miata, I'd get the 12V/DC-DC side checked even if the traction pack looks fine. That's where I'd start. On “5 miata club — anyone else: old,” that was the fork that mattered for me. This is from a 2024 Mazda MX-5 Miata in Chicago with 118,000 miles. If they can't show the line item, I assume it's hiding. If your situation is the opposite, ignore me. I keep a notes app thread for this now.
PixelMom42Community StarterCommunity StarterAug 5, 2026permalink
Checked the easy stuff on the 2024 Mazda MX-5 Miata and found one clue worth chasing before I book a shop. I refuse to clear codes until someone else sees them.
TowFanCommunity StarterCommunity StarterAug 5, 2026permalink
Low-voltage gremlins will strand you even with a full pack. Try a second charger before blaming the 2024 Mazda MX-5 Miata — site sharing and pack temp change the curve a lot. I'd do that before spending real money. I'd want a dollar figure or a measured spec, not 'should be fine.' Heat soak after errands is the other window.
TireRider24Community StarterCommunity StarterAug 6, 2026permalink
Asking because it changes the advice: Match starting SOC and battery temp if you're comparing 2024 Mazda MX-5 Miata charge sessions. Then you'll know the next fork. Write the result down so the next test isn't a repeat of the last one. That's my plan before I call anyone.
TireRider24Community StarterCommunity StarterAug 5, 2026permalink
Low-voltage gremlins will strand you even with a full pack. Try a second charger before blaming the 2024 Mazda MX-5 Miata — site sharing and pack temp change the curve a lot. I'd do that before spending real money. Write the result down so the next test isn't a repeat of the last one. Your commute and mine probably aren't the same, but the test still applies. If the story changes I'll post the new data.
QuattroSellerCommunity StarterCommunity StarterAug 6, 2026permalink
Asking because it changes the advice: Match starting SOC and battery temp if you're comparing 2024 Mazda MX-5 Miata charge sessions. That's where I'd start. I'd want that in writing, not as a promise. Make the next action something you can finish this week. Not interested in a five-hour wait for a shrug.
TowFanCommunity StarterCommunity StarterAug 5, 2026permalink
Charge curves lie if you don't match starting SOC and temp. Match starting SOC and battery temp if you're comparing 2024 Mazda MX-5 Miata charge sessions. I'd do that before spending real money. Run the total, not the monthly, before you commit. Trying not to diagnose from the couch.
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