Short Killing Battery: Relay A Suspect

I was told that a bad relay was draining and killed my battery. So after installing a new battery, I turn off battery switch whenever I leave the car for any period of time. I'm going to bring it in be be fixed, but does anyone know anything about relays -- and how many of them there are in the car? Thanks. /ubbthreads/images/graemlins/driving.gif

I don't which model you have, but let me give you some hints.

First, get a wiring diagram. Trying to sort out an electrical problem without one causes exteme madness only cured by generous consumption of ethanol.

Most British cars have similiar wiring. Brown means hot at all times, white hot with the ignition, black ground, etc.

I don't know about your car in particular, but many cars have an ignition relay. This realy, despite the name, has nothing to do with igniton. It just sends power to various circuits when the switch is on.

Get a VOM. Pull all the fuses. WIth the VOM, jump where a fuse was. With the ignition off, there should be no voltage. Repeat with every fuse. With a little luck, you will have found the ciruit with the problem. From there on, you just have to trace the ciruit.

Another possibility is in the alternator. Bad diodes can ascause a drain. With everything in place, disconnect the negative cable from battery, and connect the VOM between the cable and the battery. If everything is off (except maybe an electric clock and the radio with an electronic memory) you should have no current. If there is current, disconnect the alternator and check.

good luck.

Most cars like Jaguar will show about .03 amperes of current with the ignition switched to off and all lights, etc., off. The current is measured by an ammeter being hooked between the negative battery annode and its ground cable fitting, with the fitting off of the annode. If it is over .05 amps, there is definitely a battery drain. If your car is an XJ6 newer than an 87, you have to wait for the timers and memories to time out before the .03 amps is achieved. This takes about 5 minutes. If your drain is very large like over .1 amps, it is usually the alternator with bad diodes. Look for obscure lighting that hasnt been turned off by a switch like under hood or in the trunk. You should use an ammeter rated for 10 amps. Another source of a drain is the passive seat belt retractors. The switch can fail in the mechanism and allow the actuation motor to run all or most of the time. The bulk of this advice is applicable to the XJ40 style sedans. What model Jaguar do you own? Jack Farrington.

Thanks guys. I'll pass this on to my mechanic.

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