Here is how to disconnect car battery cables safely: take the negative cable off first, and put it back on last. If the battery is coming out, the positive cable comes off second and goes back on first. And if you are reaching for a wrench because the battery keeps going flat, it may make more sense to book a battery and charging system test with our service team first.
This guide covers the steps, why the order matters, what a Ram owner can expect once the cables are back on, and when pulling the negative cable makes sense for a truck parked through a Manitoba winter or a busy seeding season. If your real problem is a truck that will not start after a few nights parked, begin with our post on why a truck battery drains overnight.
The Ram steps below quote the 2022 Ram 2500 and 3500 owner's manual. Where your own truck's manual differs, follow yours.
Key Takeaways
- Negative off first, negative on last. The positive comes off second and goes back on first.
- For a truck that is only going to sit, the negative cable is enough. Ram's manual lists "Disconnect the negative cable from battery" for a vehicle stored more than three weeks.
- Expect a few resets. Radio and other stored settings can be lost, and the manual gives a reset for a power window that stops closing on its own.
- A diesel may have two batteries. Ask our service team how to handle both before that truck sits.
- Disconnecting stops a drain; it does not find one. A battery that keeps going flat needs a test.
Why the Negative Cable Comes Off First
The metal of your truck is part of its electrical circuit. The negative cable is the ground side, tied to the truck's metal, which is why Ram's own boosting steps put the final clamp on engine ground and warn against putting it on the dead battery's negative post.
Take that cable off first and the circuit is open. If the wrench then brushes a fender while you loosen the positive clamp, nothing happens. Loosen the positive first with the negative still connected, and a wrench that touches the positive clamp and bare metal at the same time makes a short circuit right beside the battery.
That matters because of what a battery gives off. The Canadian Centre for Occupational Health and Safety (CCOHS) notes that "Hydrogen gas is produced during normal battery operation," and tells anyone servicing a battery to "Keep metal tools and other metallic objects away from batteries to prevent short circuits."
Before You Pick Up a Wrench
Shut it down properly. The manual's boosting section starts the way you should: "Apply the parking brake, shift the automatic transmission into PARK and turn the ignition OFF."
Protect your eyes and hands. CCOHS says batteries should be handled in well ventilated areas, and calls for splash proof goggles and gloves. Ram's manual adds taking off metal jewellery such as rings, watch bands and bracelets, and both Ram and CCOHS say not to lean over a battery.
Mind the fan. In the manual's words: "Take care to avoid the radiator cooling fan whenever the hood is raised. It can start anytime the ignition switch is ON."
Find the battery. On the 2022 Ram 2500 and 3500, the manual says the battery is "located in the front of the engine compartment, behind the driver side headlight assembly." A Ram 1500 or another model year can differ. The positive post may also wear a protective cap you lift to reach it.
How to Disconnect Car Battery Cables, Step by Step
- Find the negative terminal. The negative cable is normally black, and Ram's manual notes the posts are marked positive (+) and negative (-) on the battery case.
- Loosen the clamp nut and lift the clamp off the post. CCOHS calls for the proper size wrench on clamp nuts, and says to "Use a cable puller to remove a cable clamp from the battery terminal."
- Stop there if the truck is only going to sit. The manual's storage step is one line: "Disconnect the negative cable from battery."
- If the battery is coming out, the positive cable is next. It is marked with a plus sign and normally red. Then undo the battery restraint, a bar across the battery or a clip.
- Lift with care. CCOHS says to "Use a battery carrier to lift a battery, or place hands at opposite corners."
On a Diesel, Check for a Second Battery
The 2022 manual notes that a diesel engine may have two batteries. Its storage step is written for one negative cable, so on a two battery Cummins truck, ask our service team whether both negative cables should come off before it sits.
Putting It Back Together
Clean the connections first. CCOHS lists removing corrosion on the terminal posts, and using a brush to clean dirt from the terminals and cable clamps, as part of servicing a battery.
Positive first, negative last. Reconnect the positive cable to the positive post first, then the negative cable last, and make sure both clamps are tight.
Match the posts. Ram's manual calls it "essential" that the positive cable goes on the positive post and the negative on the negative, and adds that "Cable clamps should be tight on the terminal posts and free of corrosion."
Wash up. The manual warns that battery posts and terminals contain lead and lead compounds, and says to wash your hands after handling them.
What to Expect After You Reconnect
Some settings may be gone. With the battery off, stored settings such as radio presets can be lost. Plan on setting your radio stations again.
The clock. On a truck whose Uconnect settings include Sync Time With GPS, the manual says of that setting: "The system will control the time via the GPS location." If the clock reads wrong afterward, look there first.
Power windows. The manual says that if the window's Auto-Up feature stops working, "the window probably needs to be reset." Pull the switch up to close the window fully and hold it two more seconds, then push it down firmly to open the window fully and hold it two more seconds.
Anything else. If a warning light stays on or the truck does not run the way it did, book a diagnosis rather than guessing. Diagnosis is work our service department does.
When Disconnecting Makes Sense in Manitoba
Winter storage. The manual's mark is "If you are storing your vehicle for more than three weeks", and the battery step under it is the negative cable. The same page adds that any time the vehicle is stored or kept out of service for two weeks or more, you should run the air conditioning at idle for about five minutes on fresh air with the blower on high. Disconnecting is one part of putting a truck away, and our guide to storing a vehicle for winter in Manitoba covers the rest, from MPI Lay-Up coverage to fuel and mice.
The farm truck that sits through seeding. On a grain farm in the Central Plains, the spare half ton or the older three quarter ton can sit in the yard for weeks while everything else goes into the tractor and the drill. If it will be parked longer than three weeks, that is the manual's mark for pulling the negative cable. Tape a note to the steering wheel so whoever grabs the truck in June knows why it will not crank.
When a Disconnect Is Not the Fix
Pulling the negative cable keeps a battery from being drained while a truck sits. It does not tell you what was draining it, or whether the battery has enough left for a cold start. Our post on testing a truck battery before winter explains why a voltage reading alone is not a winter test.
If the battery is already too flat to start the truck, boosting is a separate job with its own clamp order, and Ram's manual puts the last clamp on engine ground rather than on the dead battery.
Battery replacement and charging system work is work our service department does. When you book a battery and charging system test online, tell the team how long the truck sat, whether it has two batteries, and anything added to it since new. If the battery does need replacing, ask our parts department about the battery your truck takes.
FAQs
Which battery terminal do you disconnect first?
The negative, marked with a minus sign and normally black. It comes off first and goes back on last, so a wrench that touches metal while you work on the positive cannot complete a circuit.
Should I disconnect my truck battery for winter storage?
If it will sit more than three weeks, the 2022 Ram 2500 and 3500 owner's manual says to disconnect the negative cable; check the manual for your own truck. Expect radio and other stored settings to reset when you reconnect.
Can I disconnect just the negative cable?
Yes, for storage. The manual's storage step names only the negative cable. Both cables come off when the battery is being removed, or when a fast charger is used with the battery in the truck.
Do I have to disconnect the battery to charge it?
For a fast charger, yes. The 2022 Ram 2500 and 3500 owner's manual says: "If a 'fast charger' is used while the battery is in the vehicle, disconnect both vehicle battery cables before connecting the charger to the battery." For any other charger, follow the charger maker's instructions.
What do I need to reset after reconnecting?
Plan on your radio stations and possibly the clock. If a power window no longer closes on its own, use the manual's Auto-Up reset described above.
Can Dunn Ram Trucks test my battery?
Yes. Battery replacement and charging system work is work our service department does. Book a battery and charging system test with our service team.
The Bottom Line
The order is the whole trick: negative off first, negative on last, and nothing metal bridging the positive post and the truck while you work. For a truck that will sit more than three weeks, Ram's manual says the negative cable is the one to pull, whether that truck is parked for a Manitoba winter or waiting out seeding in the yard.
If you are disconnecting because the battery keeps dying, get it tested first. Schedule a battery test in Portage la Prairie before the cold sets in, and if the battery is only one of several things telling you the truck is tired, have a look at our new Ram 2500 inventory.
Tyler Dunn, Dunn Ram Trucks, Portage la Prairie
