1974 260z current drain

[Dolfinz]

I'm using the 10A scale on my DVM to measure the current.  With VR and alternator disconnected the draw is fluctuating from 200mA to 500mA.  If I disconnect either fusible link it goes away.  If there is a partial short in the harness I'll need to identify an approximate location such as between alternator and VR or fusible link and starter or something like that.

[Zed Head]

21 hours ago, Dolfinz said:

If I disconnect either of the fusible links the current draw goes away

This is odd.  Kind of implies that you're wiggling a wire when you're removing the link and removing the short.  Can't think of how disconnecting the two separate fusible link circuits separately could stop the draw.

Weird stuff.  It started with removing the VR lowered the draw, then both alt and VR out still had a low draw, now disconnecting either fusible link separately removes the draw.

One problem with your posts is that you leave things out in your descriptions.  Like in the post above you said either link disconnected removes the draw.  But you didn't confirm that the VR and alt are still disconnected.  Plus you don't give the numbers.  You've had numbers from 0.2 to 3 amps.  

It would probably help if you made a table showing the numbers with each condition.  VR alone, alt alone, each fusible link, combinations of each.  Actual numbers.

 

Edited December 12, 2022 by Zed Head
cause > stop

[Dolfinz]

With the VR and alternator disconnected I still have a fluctuating draw of 200-500mA.  If I disconnect either fusible link the current draw goes away.  I am trying to determine what/where an issue could be that is still causing this additional current draw.  We have already determined that the draw in excess of 3A is due to the faulty VR; which is why I am leaving the VR and alternator disconnected and am now focusing on this additional draw.  If I remember correctly from troubleshooting a different issue the current path starts at the battery then goes to starter then to FL1 to shunt to FL2 to?  Can't remember the rest of the path before it gets to the VR.  It would appear the draw is somewhere between the starter and the VR.

[Captain Obvious]

I don't have a silver bullet for the problem, but I can at least explain why pulling either one of the fusible links kills the draw... The larger (black) link feeds the smaller (green) link for a number of the electrical systems. Goes like this:

White wire from the battery (picked up at the starter) goes to the larger link.
Other side of the larger link goes into the shunt.
Coming out of the shunt, the White/Red then powers the smaller fusible link.
And then from that smaller fusible link, it feeds a number of systems in the car.

So armed with that info... If the larger link is pulled, the smaller link always goes dead. So pulling the large link kills power to both of the links.

You're looking for something on the downstream side of the smaller link. Those things include such items as turn signals, wipers, heater, dash gauges, etc. Essentially anything that is only powered when the key is on.

So..... @Dolfinz, you said it fluctuates. Is it regular, or seemingly random? If it regular cyclical, I'd look at stuff like the turn signals or the key in lock buzzer.

[Dolfinz]

This is a constant current drain that fluctuates when the key is off.

[Yarb]

Dome light contacts in the door jamb, turn signals. Something down stream.

[Zed Head]

16 hours ago, Captain Obvious said:

White wire from the battery (picked up at the starter) goes to the larger link.
Other side of the larger link goes into the shunt.
Coming out of the shunt, the White/Red then powers the smaller fusible link.
And then from that smaller fusible link, it feeds a number of systems in the car.

Thanks Captain.  That was kind of in the back of my mind but I didn't follow it out.  

With the wiring diagram and the knowledge that there must be a path to ground that is not supposed to be there, there are many ways to narrow things down.  Even a meter set to beep mode.  Unplug connectors and probe pins for paths to ground.  Unplug connectors and watch amperage.

[Zed Head]

Break it down in to pieces.  CO narrowed things down above.  Keep going.

The most important finding so far might be that the problem is not a simple "replace a part" problem.  Saved $30 on that VR probably.

[Zed Head]

2 hours ago, Dolfinz said:

This is a constant current drain that fluctuates when the key is off.

This is not precise enough.  You need the numbers.  Yarb makes a good point about things that might be getting stuck.  Buzzers, light switches, corroded relays, corroded switches.  For example, the dome light has constant power.  The light comes on when the circuit is grounded, either by pressing the light itself, or when the door is opened.  The switch is in the door jamb (I think).

You could also try pulling fuses and watching the current.  Eventually you'll find the circuit or circuits that are passing the current to ground.

I did take the time to look at the diagram and see that there is a lot of stuff that has constant power.  And lots of connectors.  Really looks like a PITA.  The black and white diagram hurts my eyes to try to follow.  One blink and you have to start over.  That's why being methodical and taking good notes will really help.  

Edited December 13, 2022 by Zed Head
+ on

[Dolfinz]

Sorry all been traveling for work and just catching up.  Can anyone provide me with a clear way to verify that the additional current drain with the VR and alternator disconnected isn't in the engine harness prior to reaching the fuse box and terminal block?