Current Leak?
 

In trying to find my intermittent headlight short circuit (blown fuses), I came upon a mystery. With every switch in the car off, my Ohmmeter showed about 500 Ohms from the battery to ground. On my 12v car, that would result in a current leak of 24 milliamps, with the car turned off. That drainage would be pretty typical in a modern car with a lot of "keep alive" computer stuff, but for an old Ford, it should be completely open circuit, or zero drainage.

The only hot circuit that is not on a switch is the horn. Maybe the leakage is through that foam ring that insulates the horn ring from the column.

Any ideas?

Re: Current Leak?
 

In my 1934 truck, I had the same type of short. When I would activate the system via the battery cut-off switch, I noticed a very slight jump in the ammeter in the discharge direction. The tail light would come on dimly. Down at the lower left of the engine was a bundle of wires which included the always-hot horn wire and the wire which went back to the tail light. In the bundle, both of the wires had a joint next to each other. The joints were not pushed together completely, and in the darkness I could see the current jumping from the horn wire to the tail light wire through these joints.

Simple fix - I separated the joints and thoroughly insulated those and all of the rest of the wire joints. Problem solved.

Re: Current Leak?
 

have an alternator?

Re: Current Leak?
 

Even if your light switch is off it still has power coming to it and that could be the problem. You have some sort of a partial short and the best way to find it is to systemically remove one circuit at a time to see which one makes a difference.

Re: Current Leak?
 

The ohmmeter is not measuring a current leak. It is measuring the resistance (conductivity) from one meter probe to the other. I would think your ohmmeter should have measured zero resistance. Infinite conductivity.

To look for a current leak, use the ammeter function of your multi-meter. Disconnect either battery cable, one probe on the battery post, other probe on the cable. Measures current running to/from the battery.

Re: Current Leak?
 

Yes, a little one stuffed inside of a generator look-alike housing. I will try disconnecting it to see if the current drain goes away. Good thought!

Re: Current Leak?
 

Of course the battery was disconnected at the time of measurement. The 500 Ohms was from the disconnected battery cable to ground.

I will put the meter in DC current mode and connect from disconnected battery cable to the battery terminal to see what the actual leakage current is.

Re: Current Leak?
 

The ohm meter should read 0 ohms unless there is something like a clock with modern guts running. A short which will lead to a fire or blown fuse will give you infinity but here we have a partial short or draw the owner is not aware of.

Re: Current Leak?
 

fordor41>>>have an alternator?>>>>


Yes, the sensor in a 1-wire can leak as much as a 100mA. The sensor on a 3-wire can also leak as much unless it's switched.