Switch on Amp Draw Short

Brobrian

Brobrian

Senior Member
When I turn on the switch in my pickup the ammeter jumps to show a few negative amps.
If I'm right, this should not be the case and probably indicates a short somewhere on the coil side of the switch wiring. Does that sound correct?

For those interested in the full story:
I went out the morning to run a few errands and found the battery dead. It was cold (for SoCal) so I figured I'd just throw a fresh charge on it just to see if I'd left my brake light on again. Anyway, in the process I noticed that the wiring between the alternator, starter/battery, and the terminal box showed signs of being over heated (melted insulation seeping out through the weave). I replaced this little loom and the starter switch which had been misbehaving. After reattaching the battery the car fired right up but was charging at over 20 amps. I let it run for a few minutes while I checked to see that the battery poles were connected and not touching anything untoward. But the charge rate didn't go down. I felt the wiring and the ammeter but didn't notice any heat.

:confused:It shouldn't have drawn a charge at all on a freshly charged battery. Then I noticed that when I turned on the switch with the car not running there was a discharge. It had been doing the for some time, but since the alternator only showed a charge for about a minute after a start, I didn't think much of it.
 
Brobrian said:
When I turn on the switch in my pickup the ammeter jumps to show a few negative amps.
If I'm right, this should not be the case and probably indicates a short somewhere on the coil side of the switch wiring.
Click to expand...

Well I'm thinking if your points are closed when you turn on the switch you will have current flow to ground... :cool:
 
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as Y- Blockhead mentioned that is normal if the points are closed to have a slight negative reading on the amp gauge with the (KOEO)key on engine off.
 
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If you want to check things then make sure with the points open(popsicle stick inbetween the points) check the amp meter to see if you see a discharge when you turn on the ignition key.
Make sure you don't have any loose electrical connections, and a good ground and a auxilliary ground strap from the ground cable attachment at the cross member behind the battery over to the transmission. The alternator doesn't like poor connections.
I use a master shutoff switch with my alternator. I have had a drawdown of the battery if I don't drive the car for a while.With a weak battery the drawdown is overnight. You might have your battery tested.
Bob
 
If I used an alternator, I would use a fuse and pull the fuse at the end of the day, or install and turn off a master disconnect switch. Running a battery dead is very hard on it and shortens it's useful life.

The coil will draw about 4 amps with the engine not running, but the key on and points closed.

A 4 to 6 amp battery charger will bring up a dead battery fairly well after 8 to 12 hours, but an overnight charge whould bring the battery up to full strength. If you go driving for several hours you should see the ammeter settle back toward zero. I'd check the voltage at the starter switch with the engine running at fast idle.
 
Short trips in the winter are hard on the motor. The engine doesn't get warmed up enough to drive off moisture that gets in the crankcase. You would notice milky oil on the dipstick. Also, you draw down the battery, and it can't recover.
I don't have a rule of thumb for you, but running the motor to warm it up is the general idea. I would think Tom's comment of driving for a couple of hours gives you an idea of what I am talking about. The rest of the year the grocery getting would not bother the oil so much. The winter conditions in southern california don't match the midwest, but short trips in cool weather don't do the motor alot of good. Not as easy to put your hand on the head as a harley, but yoiu get the idea.
Bob
 
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A bad diode in the alternator could cause a draw while sitting--or ignition turned on depending how it is wired ---you haven't said how much the car has been modified from stock, with the stock system only the ignition is in the ignition switch circuit, and with closed points will show on the ammeter- depending on how the connection is made ---if you disconnect the alternator and the discharge goes away then most likely there is alternator problems---diodes, even regulator could be shorted "on", causing a high constant charge, yet discharge the battery when parked ---stock systems are easier to diagnose , --- modified systems create more of a challenge because there are many variations in modifications
 
you can easily ck for a draw on the battery by disconnecting either one of the battery terminals off the battery post and connecting a simple cheap 12 volt test light between the battery post and the removed battery cable end. if the test light lights at all, even very dimly there is a draw. you can do a proof test by turning the lights on or any load and you will get a light from the tester.
once you see you have a draw disconnect individual electrical components / circuits till the light goes out to locate the suspected component
 
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Ok, I'll monkey with it this morning. I'll open the points and check to see if there is a discharge with the key on. Currently, the discharge is about 4-6 amps, so sounds like that not going to be an issue. However, I'll also check alternator by disconnecting it, and I'll reinspect the ground strap connection to the frame. I'll also, do the draw test Mitch described.
We'll see. It's a beautiful new year's day here in SoCal and a great day to tinker with the A's.

Tom, I feel bad that I haven't gotten around to sending you my generator. I think about that every time someone posts on these issues. Be assured, I'll get back to it and the car will be running its original style electrics. Anyway, I'll put a 2 amp slow charge on the battery to see if the alternator stops charging so much. As I mentioned, up to now I'd only see a charge on the ammeter for a minute or two after each start. It spooked me to see it charging over 20 amps for a the 5 minutes or so that I let the car run. Didn't want to fry another ammeter or catch some wire on fire.
 
Mischief Managed, again!
This morning I checked the amp discharge with the points open. No discharge. So, the 4-6 amp discharge was the coil with the points closed. No malfunction there.

After checking the connections, I started the car and ran it for 5 minutes and the charge rate steadily dropped to under 10 amps before I had to shut it down to take care of other things.
In the end I guess I was just spooked by the 20 amps and the evidence of overheated wires.
All seems in order now. Off to the lumber yard.

If you guys are not tired of me already, I'll post pics of the bed box I made this weekend. I really like it!
 
I made this bed box with rollers on the bottom so I can carry a few tie-downs, a gas can, and whatever my wife gets as the store without feeling like someone can just reach into the bed and take what they see.

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Thank you, Gentlemen.
Hard to know what is more fun, woodworking or tinkering with my A's. Nice when a project combines both. Sadly, I think that's all the woodworking I can to on this one. Have to wait until I redo the top of the coupe.

Again, thanks to all you great guys who give me (and everyone) good, on-target advice. It felt great to have the pickup fixed. I went to Home Depot and picked up lumber and drywall for my son. (Really put my lumber rack to the test!) By the time I had gotten there the ammeter was reading zero again and all was right in the world.
 
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