tracing a possible electrical short

[Captain Obvious]

4 hours ago, SteveJ said:

I think you are muddying the waters this time,

No problem. I know this is in capable hands.

I'll stand back some try to keep quiet.       

[SteveJ]

1 minute ago, Captain Obvious said:

No problem. I know this is in capable hands.

I'll stand back some try to keep quiet.       

It doesn't hurt to make sure RJK knows that he's probably reading light bulbs.

Actually, one time I was trying to find a battery drain on a 280Z. I started at the fusible links and moved down to the fuse box. I only found one fuse with current flowing through it. I realized that it was the dome light circuit, and the doors were opened. D'oh! I closed the doors and measured again, only to find the circuit still had current flowing. The door switch on the passenger side was not opening when the door was closed.

I gave the owner the option of pulling the fuse or paying me to remove the switch. He pulled the fuse.

[RJK]

Well, as many I think have suspected, this looks to be filed under "user error". I closed the PS door, rechecked all switches at the steering column(headlights, turn signals, etc etc). Rechecked, and I'm now reading about 23 ohms. Well, better safe than sorry, I guess. I think the experience of watching the insulation burn off a wire in real time kinda traumatized me. I'm gonna button everything back up, save for the alternator, and make sure I'm seeing 12V at the proper wire, and then call it a day. Thanks for all the help, folks!!!

[SteveJ]

Well, there was the time I spent about 3 hours trying to figure out why my battery voltage dropped to zero as soon as I turned the key to ON. I was sure there was a short. I just had to disconnect the right thing...

Oh, the battery was bad. It had potential, but it didn't have the energy to drive current. As soon as it had a load, there was no more potential. 

Now, you can think that you wasted your time, or you can realize that you learned something about how to diagnose electrical circuits with an ohmmeter.

Okay, it's time for one more door open story. Around 40 years ago, my brother was installing a new stereo into the family's 68 Mustang. He needed to find a wire that went to ground. Searching around, he found one. He finished the install, and the stereo was cranking out the tunes. So after putting tools away, he got in the car and was going to drive around and enjoy blasting the music, only the stereo wasn't working anymore. So he stopped, got his tools out, but the stereo worked fine again. Shortly he realized that the ground wire he selected happened to be downstream of the dome light. When the door was open, the switch was closed, and the stereo worked. With the doors closed, the stereo lost its ground. He found another ground wire for the stereo.

[RJK]

I appreciate all your help, guys. I am honestly fine spending the time on this, if the end result is A)I'm confident in my wiring, and b) I learn some things about diagnosing electrical issues. Thanks!

[SteveJ]

8 minutes ago, RJK said:

I appreciate all your help, guys. I am honestly fine spending the time on this, if the end result is A)I'm confident in my wiring, and b) I learn some things about diagnosing electrical issues. Thanks!

Good. That's exactly what my intention was.

[RS02]

Thought I'd chime in on some minor info. MSD ignition boxes uses some BIG capacitors to filter input voltage and charge the coil. The constant 12v wire will spark when you first connect it to a voltage sorce.