i was cleaning my terminals and noticed that it sparks when i touched the connector to the battery terminal. this tells me something is placing a small load on the battery. i checked to ensure the inside light was off as was everything else.
at random, i disconnected the three wire connector leading to the distributor. the sparking stops.
it's my understanding there should be no load on the battery with everything off.
what do you suppose could be causing this.
bad alternator allowing current to run back through a shorted diode or what?

 

Which cable ?

You should ALWAYS dis-connect the Ground cable first
and
put it back on LAST.

What you experienced was the ALL The TIME power circuits getting re-energized.

Things that have power all the time:
Clocks
Stereos


Hmmm...What else?

 

Which way do you have the starter relay wired? Is the cable coming from the battery on the big stud closest to the small "S" terminal or is it on the "I" terminal side?

 

Macguyver: If it starts; its right.
I'm not sure it really matters. I just replaced the starter relay on my '85 F250 351W and the directions for new one did not specify which big lug the battery or the starter should connect to. I took the old one apart and it didn't appear that it made much difference. When a voltage from the ignition switch is applied to the "S" terminal it charges the relay coil which moves the slug and closes a set of contacts between the big terminals or lugs. It doesn't seem to matter which way the current flows between those big contacts. For ease of connection I put the battery cable on the big terminal closest to the battery and the switch-starter cable on the other side which, in my case, meant the battery cable was closest to the "S" terminal.

I also would be interested to know if there is a difference. One thing I did learn. Don't buy the cheapest relay you can find. The contacts and coils burn out pretty easily.

Russ

 

There's no difference (polarity) to the big terminals.

 

The only thing he is talking about is the current draw from his accessories.
It sparks because they get energised.

 

frankster123--
Diodes never short internally.

Mil1ion--
"It sparks because they get energised." It sparks because the components are not energized/ high current situation.

OK, call me ****.

 

OK guys, what made me ask about the "polarity" of the starter relay is the fact that the sparking went away when the distributor connection was disconnected. Normally there shouldn't be any draw through there when the switch is off. I know there's no difference on the two big terminals but when the relay is energized, a connection is made between the main disc that connects the two mian lugs and a small brass "lead" that goes to the "I" terminal to provide battery voltage to the ignition. Ever taken a relay apart to see what's inside? I have. That small brass lead is located pretty close to what is normally the lug to the starter (non-energized, no voltage). Now if, and I know it's a pretty big "if", that brass lead has some sort of connection to the "now" battery terminal, it could be providing a current leak through the ignition system. I've seen that brass lead get distorted/warped and if the fallout from the main contacts creates a bridge to the "I" terminal, there's the drain. I know it's a long shot but how long does it take to remove the wire to the "I" terminal to check it?
Just my 2¢
Greg
p.s. any capacitors to stabilize battery voltage will take a small surge to energize them. A good way to check for a drain is to connect a test light between a disconnected battery terminal and the cable. The light will keep enough voltage on the capacitors to keep them energized but they won't draw enough to keep the test light on.

 

thanks, all of you for your replies.
i was, many years ago, an electronics technician. still, with that experience, i can't see how or why there should be current flowing when everything is off.
i'm not sure about diodes shorting. i've heard people say alternators fail by allowing current to flow back through the alternator after the alternator has been charging the battery. whatever charging it has done will leak back out through the defective alternator.
i don't understand why there should be current flowing through the distrubutor.
i noticed today that my truck was a little slow turning over when i started it. it appeared the battery was low but later it was alright.
if the truck how points, which it doesn't, i might think the points was closed and the ingnition switch was shorting, or something.
i hope one of you has another idea.

 

If you do have a two terminal starter relay, I would try what macguyver said, and take the wire off the "i" terminal. If you only have a single terminal starter relay, then you need to try a few other checks on the distributor to verify it is the culprit.

Take a voltmeter and see if you have any voltage on:

The red wire going to the module

The white wire going to the module

The (I think it's red/green) wire going to the positive of the coil.

If you have voltage on any of these terminals with the the key off, you definitely have a problem, and it could be with the ignition switch, or possibly there is some homebrew wiring somewhere that is messing it up.

 

The most common diode failure mode IS shorting. The capacitors
in the PCM for the KAM will also charge when the battery cable
it connected. One other thing, with the wiring inductance, and the
di/dt when the battery connection is made (or broken) will
create a high voltage.

 

Mil1ion has it right. The radio uses a small amount of power to "remember" the radio station you are set to and also to remember the pre-set stations. The clock uses a small amount too. I assume the computer is using a little power also, although I'm not positive, and Macguyver is right about capacitors drawing current when they initially charge too.

Bottom line, I've probably hooked up 100 batteries in my car, truck and motorcycle in my 62 years on this earth, and I always get a little spark. It's probably nothing to worry about, but to be sure take the ground cable off the battery and hook an ammeter between the cable and the battery. BE SURE YOU HAVE IT SET ON 10 AMP RANGE OR HIGHER. If you don't get a reading, reduce the range till you do get a reading. It probably will measure less than .5 amp. If it's registering more than that then maybe you do have a short somewhere.

WARNING: Using a range that is too low can result in a fried meter. Some of the cheap meters only go to 1000 MA which is 1 AMP. Some meters have protection against overloads and some don't. Also never try to measure the resistance of the battery or make any resistance measuremens with the power on.

 

Bob Ayers is quite correct. Diodes fail in MANY ways, however the most common is an internal short caused by thermal breakdown. Better carry extra whitey tighties when the big ones EXPLODE! Steel mills give such a wealth of experience on CATASTROPHIC failures of all kinds of equipment and components.