This project was originally published in the September 2000 issue of Popular Mechanics. You can find more great projects at Popular Mechanics DIY Central.
Step 1: Neglect Is Abuse
Step 2: Safety First
A set of 6-ft. cables won’t do you much good if you’re parked nose-in to a parking space—unless you feel up to pushing a 3-ton SUV back a truck length to make the engine compartment available. Twelve or 15 ft. is better, which makes using heavy-duty cables more important because resistance losses are proportional to the length of the cable. Keep your cables clean and dry to prevent corrosion from becoming a high-resistance factor.
Step 3: Doing the Deed
Some cars, like the one illustrated on the previous page, have a remote positive terminal someplace in the engine compartment. The battery is mounted in an inaccessible area of the engine compartment or in the trunk. As for where to attach the jumper cable, this junction will be clearly marked and covered in a red plastic sheath. If in doubt, consult your owner’s manual.
Wear eye protection, even if it’s only a pair of sunglasses. Once in a blue moon, a battery will explode when you try to jump it. Explode? Yes, explode. It’s caused by hydrogen gas, which is normally vented by a battery that’s being charged or discharged at a high rate, say, when you’re trying to start a car, the battery runs down and you need a jumpstart. Hydrogen is explosive, and a spark from making a connection can ignite it. It won’t be a big explosion, but it can certainly blow the top of the plastic battery case off and spray acid into your eyes. Connect the red clamp on one end of the jumpers to the positive terminal on the dead car. Verify the polarity of the terminals by the plus symbol molded into the battery case. Don’t just use the red terminal—someone may have installed an incorrect, red-colored terminal onto the negative pole of the battery. Do the same on the positive terminal of the donor car. Start the donor car and let it idle. Lights, heaters, stereos and rear-window defrosters—all electrical drains—should be off. If possible, cover the dead battery with a shop towel or a sheet of cardboard. Any acid that manages to bubble out of the vents will wind up on the cloth instead of on your clothes or the paint on the fender.
Connect to the negative terminal of the donor car’s battery with the black clamp. Verify the polarity. Now connect the remaining black clamp to the dead car’s engine block, an accessory mounting bracket or a protruding ear on a manifold. Use the battery’s negative terminal as a last resort. This procedure will generate any sparks far from any hydrogen gas venting from the battery and reduce the risk of explosion. Now wait. This will let the dead battery recharge slightly. It will charge more when the dead car starts, but it will help the donor car’s battery start your engine a little if you give it a quick shot of charge. If the dead car’s battery had enough charge left to make the solenoid click and run the interior and instrument lights, then a minute or so is enough. If the battery was dead, dead, dead, give it 5 minutes or so.
Step 4: Crank, Zoom
Step 5: Options
If you’re not in a crashing hurry, you might find cigar-lighter cables will get you started. These gadgets just plug into the two vehicles’ lighter plugs, providing a modest level of charging, but not carrying enough current to start a car with a truly flat battery. But if the engine will almost start, a 10- or 20-minute charge will get you on your way, out of the weather and with clean hands. Remember that the lighter socket on the dead car must be electrically hot with the key off, or you’ll need to turn on the key in the dead car to complete the circuit.