Testing for Parasitic Power Drain:
Does your VW Van or Westy lose power when it sits for a day or two?
What you want to do is test your electrical system for what is called a Parasitic Battery drain.
When your van battery goes dead overnight, usually either the battery is at the end of its life span, or you left something on, such as a light. Occasionally something is drawing power thatâ€™s not of your doing. This is a parasitic draw, and it can cause the same result as leaving the headlights on: a dead battery in the morning.
1. Remove the negative side battery cable from the negative battery terminal.
2. Attach an ammeter(this measures amperage) between the negative cable and the negative battery post. wait a few seconds to several minutes for the car to go into sleep mode. i.e. when you make the contact with the test light the cars computer systems “wake up” after a bit of time they will go to “sleep”.
3. If the ammeter is reading over 25-50 milliamps, something is using too much battery power.
4. Go to the fuse panel(s) and remove fuses, one at a time. Pull the main fuses (higher amp ratings)last. Be sure to observe the ammeter after pulling each fuse.
5. Watch for the ammeter to drop to acceptable drain. The fuse that reduces the drain is the draw. Consult the owners’ manual or service manual to find what circuits are on that fuse.
6. Check each device (circuit) on that fuse. Stop each lamp, heater, etc. to find the drain.
7. Repeat steps 1&2 to test your repair. The ammeter will tell you exact numbers.
Prime suspects that I have found over the years:
1. Fancy Radio/Amps. These have a memory or some type of capacitors, that will drain the battery over the course of a couple weeks of sitting. You can either make a switch to turn off the draining circuit, or install a battery charger so that it will keep the battery up when the van is sitting.
2. Tail lights/crappy trailer wiring. Sometimes the brake light switches will fail and this will keep the brake lights on. This is pretty obvious since you will notice the lights staying on when the van is shut off and sitting. The other thing that can happen is that someone in the distant past (or you) has installed a trailer wiring kit from Wal-mart. Are you really going to tow something with this van, ever? You really shouldn’t. Highly suspect the trailer wiring whenever the van’s electrical system does anything strange. It is always crap! I usually remove it unless the person insists that they really need it.
3. Leaving interior lights on by mistake. That light above the glove box in the Vanagon or the one above the visor for checking your makeup. You left it on you naughty person you!
PS: If you don’t have an ammeter/volt meter you can also use a test light instead. In the directions above just substitute the ammeter with a test light. I usually use a small hose clamp to attach the spike of the test light to the negative battery terminal and the wire end should have an alligator clip on it so you can attach that end to the negative battery cable. If there is a drain the light will light up. Follow the directions above until the light goes out and you should find the drain that way as well. Some folks are very scared of meters, so this is for you if thinking about a volt/ammeter makes you run for the hills ?
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