A quick question for the electrical gurus out there.
As stated in my other post, I am working on getting all of the electrical circuits up and running on my 85 XJS project car. When I got the car every electrical component was disconnected and/or disabled. I also stated that the car has a frozen engine and no ECU but that is another topic.
So far, I have most of the lights working, all telltale lamps in the instrument cluster, blower motors, window motors, side mirrors, signal lights and door locks.
The following was occurring before I started to do any electrical work on the car.
Whenever I try to connect the negative cable to the battery, I get a spark. When i remove it and connect it again, no spark. If I wait for a minute or so, the same thing happens. First touch, spark, second touch no spark.
If I connect a test lamp between the negative cable and the negative terminal, the test lamp will light up and slowly diminish until it is totally off. It will continue to stay off if I left the test light connected. If I disconnect the test lamp and wait for a minute or so then reconnect the test lamp the process repeats itself.
It is as if something stays charged and when I connect the test lamp it discharges itself.
Is this normal? Is it a short? If so can anyone enlighten me.
Because the lamp goes off within 10-15 seconds. I can't leave it connected and go to the fuses to pull them one by one to see if there is a faulty circuit.

 

Cannot help at all with your issue, but I have a similar (sort off) situation.

I have installed a separate volt meter gauge, connecting the gauge directly to the battery (earthed). as per the instruction.

I also presently have my dash out to fix up some cracks, but I have reconnected the hazard lights, (etc) to complete the loop to test my turn indicators.

I also connected my clock at the same time.

Now

With only the volt meter earthed to the battery, but the main earth lead disconnected (I have a 2 step process here). And with the + terminal totally disconnected. My clock started ticking. Also my volt meter gauge started ticking (lighting up) in time with the clock. Disconnected my volt meter earth and the ticking stopped.

I have no idea where the power to supply the clock came from. The clock had also been disconnected and was in storage for at least 6 months before I reconnected it. So it should not have had residual power

I have not noticed it doing it since - but I make sure everything is disconnected when I finish the activity I need connection

Maybe yours is similar,

Cheers
Steve

 

Maybe it was using the power from the 9 volt battery in your voltmeter?????

 

No battery in my volt meter. Connected to the old radio power supply (ignition on) white wire. Same power wire supply as my additional oil pressure and water temperature gauges. These last 2 gauges only come on when the ignition switch is on (as I expected)

My previous owner has done a lot of "modifications" - including cutting the original oil pressure/water temp gauge wiring - so I wanted a little bit more safety in the system until the original gauges are proven

Just one of those things that has me scratching my head

Cheers
Steve

 

Sanchez:

Can you measure that small draw? Radio, PCM memories? .045 milliamp sticks in my mind from somewhere.

Carl

 

The time span of the electrical short is 10-15 secs. By the time I get to the inside of the car the visible signs of the short is gone.
What i am planning on doing is the remove all of the fuses, then reinstall them one by one to see whether the test lamp will turn on when a particular circuit is completed with the fuse.
If the lamp would stay on, then I would do it the conventional way. Isolate each circuit one by one to see which one will cause the lamp to turn off.
I am also going to take a voltage reading at the battery and leave it connected the rest of today and all night tonight to see how many volts I lose in the time span.

 

Try this. With the negative battery cable disconnected, put your test light in place. When the light goes out, without removing the test light, connect a test meter set to measure milliamps. Once the test meter is in place, remove the test light so all current goes through the meter. If you are less than 25 ma, or 0.025 amp, don't worry about it. It is common for electronic components, radios, ECU's and such, to have some parasitic draw, and also common for there to be a bit of a surge when the battery is first connected. If your draw is more than 0.025 amps, I would chase it down using the meter reading.