I had to do this a few weeks ago to my Lumina to find a short that kept draining my battery overnight. This is a two person job (you need one person to read the meter).
You need the following tools:- Digital Multimeter w/ Ammeter Setting
- Hayes or Chilton?s repair manual for your car. This is not an absolute must, but you need to know where your under hood and cabin electrical centers are (fuse & relay boxes). You also need the wiring diagrams to track down the shorts when you find the circuit they are on.
- An electrical short
This Is What You Do:- Get a digital Multimeter and make sure that EVERYTHING in your car is turned off.
- Disconnect the negative battery cable from the terminal.
- Make sure the Multimeter is on the Ammeter setting and connect one lead to the battery terminal and another lead to the battery cable that runs to the car (you can ground it out anywhere though).
- The meter should say something like 1.82 0.09 or something to that effect. Give the car a few seconds to stabilize the electrical load (some cars have lights on timers, also think radios and such). Normal operating Amps should be somewhere around .03-.05 amps
- If your car is using more amps than normal, have one person watch the Multimeter while you start pulling relays (these like to fry and kill batteries). Pull all the relays in all of your electrical centers. If your amperage usage goes down that is your problem relay. Replace with a new one and plug all the relays back in, if you still have an abnormal amperage reading continue to the next step.
- Now start pulling fuses, when the amperage usage goes down to normal, you have found your problem circuit. Plug the fuse back in and continue to the next step
- Go to your wiring diagram and trace the circuit to see what's on it. Start disconnecting the items one by one and when the circuit amperage drops significantly you have found your problem. Reconnect everything and if your amperage is in a normal operating range your done, If not repeat the previous step until it does
- You're done!
There ya go, I hope this writeup helps someone out someday
