Is my old Willys pickup positive ground, and should I convert it to 12 volts?

Short answer: Check which battery post the frame cable goes to. One member found the Willys was originally positive ground, but another's old manual listed a '54 as 6-volt negative ground, so don't assume. A safe test: connect it, turn on the headlights, and watch the ammeter. Discharge means it's hooked up right; charge means it's backwards. Converting to 12 volts is doable but not a battery swap: you need 12-volt bulbs, a ballast resistor for the coil, and reducers or resistors for the gauges, blower and wiper, or a conversion kit.

Symptom: You're bringing an old Willys back to life, aren't sure how the battery should connect, or want 12 volts for a plow or modern parts.

What to check first

1. Find which battery cable bolts to the frame or engine.
2. Do the headlight-and-ammeter test before running the engine.
3. Inspect the wiring. Brittle insulation and electrical tape patches can short when you apply power.
4. If converting, list every 6-volt item: bulbs, coil, gauges, blower, wiper, radio, starter.
5. Price a conversion kit against doing the resistors yourself.

Likely causes

1. Original 6-volt positive-ground system. Positive ground means the battery's positive post connects to the frame. Many older 6-volt vehicles were wired this way.
2. Mismatched or unknown previous wiring changes. Years of patches, a side-post battery and same-color cables make it hard to know how it was set up.
3. Wanting 12 volts for accessories or easier starting. Plows and modern accessories need 12 volts. Converting means changing bulbs and adding resistors or a kit so 6-volt parts don't burn out.

What it usually costs

Owners in these threads didn't post prices.

Is it safe to keep driving?

Wrong polarity can damage parts and old wiring can arc and start a fire. Have an extinguisher nearby when you first power it up, and disconnect the battery when you're not working on it.

DIY or shop?

Yes, this is classic restoration work. Take your time and label every wire.

Recalls, bulletins and complaints in plain words

• Recalls: NHTSA's recall and complaint lookups returned no data for this model in these years, which is normal for a car this old. These trucks predate NHTSA's recall system. Check your VIN at nhtsa.gov/recalls. If your car is part of a recall, the dealer fixes it for free.
• Plain words: The complaint count below shows how often owners reported problems that mention these words to NHTSA. A count is not proof of a defect.
• NHTSA complaints: 0 keyword-matched complaints for Willys Pickup 1950–1965 (of 0 unique complaints queried, NHTSA complaints API by model year, queried 2026-10-30; keywords: electrical, battery, volt) (NHTSA returned no data for 96 model-year queries). This counts complaints that mention these words. It is not a defect finding.

What owners report

• In 1953 Willys pickup 6 volt on Car Talk, a 1953 Willys pickup owner who'd installed a new starter asked if the truck was positive or negative ground. Members said to look at which battery cable goes to the frame, and one shared a test: hook up positive to ground, turn on the headlights, and if the ammeter shows discharge it's connected right; if it shows charge, reverse it. The owner said the wiring was patched with electrical tape and both cables were black, so the usual clues didn't help. Members warned to confirm it has a generator, not an alternator, before trying the test.
• In Changing a 1950s Willy's 6 volt system to 12 volt on Car Talk, a friend's 1953 Willys pickup was being restored and they wanted 12 volts for a plow. Members said putting 12 volts into a 6-volt system will fry gauges, bulbs and switches, that every bulb must be changed, and that dropping resistors are needed for the heater blower, wiper motor, coil and gauges. Others said conversion kits exist and the coil just needs a ballast resistor.

Quick tip

Fix the wiring before you change the voltage. A tired harness that's been taped together will cause more trouble than 6 volts ever did.

Vehicle focus: Willys pickup and wagon (Jeep), 1950s-1965, original 6-volt systems.

Safety / mechanic note

Electrical shorts and fire risk are safety items. Verify with a mechanic.