Jump Starting A Dead Car Battery: A Few Precautions

	Line both cars up so the batteries are as close as can be. Make sure the cars are in park, and both cars are turned off, and not touching each other before you connect the cables. Make sure all headlights, blinkers, car radios and A/C's are off, radar detectors are unplugged, cell phones unplugged, everything off. Unplug all accessories from cigarette lighters and other power sockets from both cars. Jump starting a battery can crank 300+ volts through your system and the transients can destroy equipment. These voltage spikes are caused by inrush current, into the inductances in your electrical system.
	Familiarize yourself with the Positive (+) and Negative (-) terminals of both car batteries so you know exactly which one is which. Wipe off any battery acid that may have leaked.
	If the battery is cracked and liquid is leaking out, do not go further! Bite the bullet and go buy another battery and swap it out. If you try to jump start a battery with a crack in it, it may explode.
	Try to clean off any corrosion around the dead battery terminals, and if you have tools, loosen the wires from the terminals, clean them off, then retighten the wires to the shiny posts. Corroded posts prevent the power from getting through the cables and into your battery to revive it. If you have a file handy, try to file the metal battery posts until they are nice and shiny. In a pinch, use pliers to clamp down and scrape off corrosion too as the metal is somewhat soft.
	Usually the positive battery cable is red or orange, and usually the negative (-) or ground cable is black, but always check for yourself to be sure.

Connecting The Car Battery Jumper Cables

The cables must be connected in this exact order listed below:

STEP 1: Connect one end of the Positive (+) cable to the Positive (+) post of the dead battery.

STEP 2: Connect the other end of the Positive (+) cable to the Positive (+) post of the good battery.

STEP 3: Connect one end of the Negative (-) cable to the Negative (-) post of the good battery.

STEP 4: Connect the other end of the Negative (-) cable to a good solid SHINY, NON PAINTED metal part of the engine on the dead car. Usually a giant shiny nut on the engine block will do. A painted, dirty, or oily nut will not work. You usually want to avoid placing the Negative(-) cable directly on the dead battery to minimize the chance for explosions. You should only use the ground post on the dead battery as a last resort. On this step you'll get a normal spark as you connect the ground and complete the circuit.

Why do the Jumper Cables have to be connected in this order?

The reason why you connect the battery cables to the dead car battery first is you have 3 metal cable ends dangling and potentially touching metal car parts, so a dead battery is less likely to cause any sparking, since it has little or no voltage. That is why this is the safest starting point for your jumper cables. The 2nd battery cable clamp goes to the positive end of the good battery instead to minimize completing any circuits until we are ready to. Then the 3rd end of the battery cable goes to the ground of the good battery. Remember, we still have not completed the circuit yet, until the 4th battery cable clamp is attached to ground. This is why this order of attaching the battery cables to your car batteries is the safest way to do it. It minimizes unnecessary sparking until the charging circuit is completed. This is good practice because excessive and unnecessary sparking could cause car batteries to fail.

Since the bad battery is weak, and to prevent exploding, it's ground clamp gets connected last, but not directly to the ground battery post. To prevent sparking directly on the battery, you connect the 4th battery cable clamp to a metal frame part of the dead car, which is connected to the minus pole of the battery. Many people are easily confused by this step. They cannot figure out how this completes the circuit to the battery. Car batteries have their ground cable also wired to the chassis of the car, so by clamping to a good metal chassis point, this is electrically equivalent to connecting to the ground post of your car battery.

Gentlemen, Start Your Engines!

Start the good car's engine, and make sure the headlights are off, to allow the maximum amount of power to get to the dead battery. Let the good car's engine run a minute or so before attempting to start the dead car. Sometimes you get lucky and the dead battery will jump start right away, sometimes it takes a few minutes. If you're lucky and have a voltmeter built into your dash on the dead car, turn the key to the accessory setting and read the voltage coming into your charging system. Ideally you want between 12 and 13.6 volts, but some cars can start at 10 volts. If your dead car's interior dome light comes on, it's a great sign that you've connected the cables right. Now shut all doors and dome lights and try to start the car. If it sounds like it's trying to crank but won't turn over completely, give it a few more minutes and rev the engine moderately on the good car. You may also need to play with the cable grips to get a better connection, and use that in dash voltmeter to its fullest if you have one. You'll get a normal sparking as you move the cables around a bit. Let's assume your engine started ok, but if it did not start, see the troubleshooting section further down this page.

Removing the Jumper Cables

Now that your dead car has been successfully jump started, you can remove the cables in the reverse order that you connected them, being careful not to let the battery cable clamps touch each other:

Disconnect the Negative (-) cable from the engine block of the car that was jump started. This breaks the circuit.
Disconnect the other end of the Negative(-) cable from the Negative (-) post of the good battery.
Disconnect the Positive (+) cable from the Positive (+) post of the good battery.
Disconnect the other end of the Positive (+) cable from the Positive (+) post of the dead battery.

This page was last updated on 03/05/07.

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