Finding a parasitic draw
 

Does anyone have an easy, or at least a systematic way, of discovering your car's parasitic draw? My roadster has one and it kept me from taking it out the other day. I know what many of you will say - install a cut off switch, but I'd rather find the culprit and make the car operate correctly. Thanks in advance!!

Re: Finding a parasitic draw
 

Mine was the horn. I knew something was drawing as it sparked when I'd hook the battery up. Lucked up and could feel warmth on the horn. I believe one wire was loose.

Good luck with your problem and make sure to tell us what it is when you find it.

Re: Finding a parasitic draw
 

Remove a battery cable [ or starter fuse if one is installed] and attach a test light or volt meter across the terminals [ from battery terminal to removed cable end or across the fuse terminals] and look at the voltage reading or if the light lights. If there is battery voltage there is a draw. Keep unhooking things until the draw stops, thats your problem. Brake lights or dash/interior lights are a common issue with these As.

Re: Finding a parasitic draw
 

If you are running an alternator, often a diode will "Leak" and cause enough of a draw to keep running the battery down. A faulty diode in an aftermarket generator "cut-out" with a diode can also cause the same problem.


Install a master switch and shut the whole electrical system down when you park the car for an extended period of time.


CChris W.

Re: Finding a parasitic draw
 

If you have a volt, amp meter, like the ones you can get for free at Harbor Freight for buying something, follow the directions to read amperage place the leads between the neg terminal and the cable and it will tell you the amt of drain, then start looking, brake switch , alternator etc, when you disconnect something and the loss is gone, you found it

Re: Finding a parasitic draw
 

I have one that comes and goes on both my cars at the fuse holder. If I reverse a circuit breaker in the fuse holder on my coupe it will go dead. If I make sure the shiny rivet is forward in the holder I'm good to go. Reverse it and soon the battery is low or dead. With meter across the fuse holder I cannot get a reading nor will it turn on a trouble light, yet I can see a spark at night if I break or make the contact across the fuse holder. Been that way for years. For a few days recently it would eject the fuse or circuit breaker with enough force to throw it onto the ground under the car. It did that several times and then it quit and is acting normal for the last several days. Got me, Gremlins I believe, though I haven't found a "Kilroy was here" note yet, I won't be surprised if one turns up. Twice while driving slowly the fuse was ejected onto the street and once while parked it shoot out of the holder when I was watching it and had my wife hit the starter switch. Picked it up, wiped it off and put it back into the holder and drove almost home, as I entered my driveway the engine died and the circuit breaker was again under the car. Put it back and parked, haven't touched it but have driven the car probably 10 time, once for several hours with no problems. I you can figure that one out, let me know. I haven't a clue.

Re: Finding a parasitic draw
 

How about, The circuit breaker is more top heavy then just a fuse and as the current passes thru the metal ends on the fuse holder it heats them up and they lose their gripping power and the circuit breaker just falls out.

Re: Finding a parasitic draw
 

The attached document may be of help. it is designed to locate a dead short that blows the fuse. However, the same logic can be applied when looking for a power drain. The idea is to isolate the source of the fault into one of three areas.

Tom Endy

Re: Finding a parasitic draw
 

About Post #6.

Davey

Sometimes Kilroy uses invisible ink!:D :D

Try shinning an ultra violet light around...

Also in 1968 at AnKhe we sometimes found only very small yellow Cav Patches with no text.
[/B]
Seriously … one time I had a VERY intermittent short in a Coupe.

1. There is a wire going out of terminal box (black and blue as I remember might be wrong on color ... it was over 50 years ago!) that goes to the wiper motor and interior dome light.

It was shorted where the wire goes up the side of the windshield. Opening and closing windshield would sometimes cause the short!

Very hard to find!!

2. Another thought. Maybe the wiper motor gearbox is full of dried up grease and the switch is left on sometimes.

This happens when kids are "driving".

Re: Finding a parasitic draw
 

Thanks as always! I'll give these ideas a try. Looks like I just have to dive in.

Re: Finding a parasitic draw
 

Here is another place to look. I recently rebuilt my AA starter. When I tested the field coils they tested ok for continuity but also showed a high resistance to the shell; ‘leaky’ insulation. I pulled the fields out and gave them a good coating of electrical insulating varnish and no more leaks. This would no doubt have had the potential to become a parasitic draw as you describe it. I also tested starter switch and it tested ‘leaky’ also. This is a good place to look also. Carbon, which is an excellent conductor, can build up in the switch insulation (from repeated arcing of contacts) and cause a leak there.

Re: Finding a parasitic draw
 

Wow - that sounds like it took a while to find. Thanks!!