Odd black wire

[VonMussa]

I can’t figure this connection/black wire out. Does anyone have any ideas?

Matt

[bikermike]

Have you looked at the wiring diagrams in the Tech Wiki?

If the ballast resistor has been removed, it may be a wire used in the past for that.

[rwmann]

Typically black would be ground, so perhaps the negative pole of the nearby coil?

[Curtis]

Where is it coming from? That is not a stock connector on it.

With the stock ballast resistor being used you have coming out of the firewall yellow/blue for the S brake switch, black/white, black/white with red band, black/white with white band. A short black/white wire from the resistor to coil. A black wire that loops around in the harness from the coil to the distributor.

Top half of the drawing shows them.

http://kendo-usa.org/datsun/resistor_bypass.pdf

[rwmann]

Black lead appears to emerge from the harness through the firewall ahead of the fuse box, no?

[Curtis]

Black lead appears to emerge from the harness through the firewall ahead of the fuse box, no?

The stock black wire never enters the firewall. only the black/white. If he has a black wire entering the firewall then it is sins of PO.

[VonMussa]

Yes. That black wire dives right into the firewall.

I just installed an ECR EI and she was idling PERFECTLY. So of course I opened the hood to see what else I could screw around with. My buddy saw that black wire, assumed it was Supposed to be hooked up to the negative on the coil. And the car wouldn’t start. Took it off. And it runs. Really weird. I of course screwed a lot more up in the process, there will be another thread shortly for more help.

TL/DR: defintely sins of PO

[rwmann]

Bingo... OP magical thinking.

[jake7140]

I have the same wire and confusion. It has a hard protective cover around it and comes out of the harness that the brake light wire and the bk/w ignition wires come out from. It looks very stock to me, having the same terminal covers as the ignition wires. My tests:
- the ballast resistor is present and wired, but I believe it to be gutted as I get battery voltage on both sides
- running a EI dizzy and blaster coil, though initially it was stock dizzy with capacitor and same coil
- with ignition in 'run', car not running, I get battery voltage
- with car running, I get -1 to -2-3v, varying slightly with rpm. Larger negative with higher rpm
- if I touch to + on coil, car dies
- there was continuity to (forget now) 1 or 2 wires in the harness plug to the regulator
- I have installed a new, electronic 510 regulator

I have been having overcharging issues, and was hoping this wire may provide feedback/battery voltage for the voltage regulator. PO had done some funky wiring, including disconnecting stock alt wire and running a wire directly from alt to battery. Yikes. I removed that and found original white wire. Also the temp sender and wash pump wires. Ammeter then working properly, but still overcharging. Harness from regulator to alternator had continuity and no shorts on all wires. Tried three different relay style regulators from the parts box. All overcharged. Alternator tested good,no shorts. Alternator guy suggested the sensing wire not getting current battery voltage to inform regulator to do its thing.

With the new regulator, my last short run test (exhaust not reconnected,late at night) showed no variation in battery voltage when running at idle to about 2k, after extended cranking to start. Couldn't see ammeter.

I'll put the car back together and run some more tests. But that dangling black wire has always had me confused. I have been through wiring diagrams, including Curtis' harness diagrams and see nothing I can relate it to.

As I look deeper, perhaps the coil and balast resistor wiring is wacky as I just noticed the little red and white rings on the bw wires. Per diagram one of those does go to the regulator, i suppose to feed battery/ignition voltage to the VR. Could also check voltage on that wire at the VR.

20210517_011104_copy_1008x567.jpg

[JT68]

Pretty sure that is your old points wire?? Nissan made it confusing by routing that plain black wire from coil- into the harness, into the firewall, back out and over to the points. Wacky.

If so, Tape off both ends, neither should be connected with EI.
Your coil -minus should have ONLY ONE connection -either the black wire to the EI or the points wire. Not both and nothing else.

Since yours is a late car, there are TWO required positive harness wires for the coil+:
B/w +red only powered on “start”
B/w + only powered on “run”
Both get attached to coil+ AND the red wire to the EI.

There are two wires for the resistor too. Those get taped off if not using a resistor.
(One has +12 on it since it is B/w)

regarding the regulator wires:

There is no connection at the coil for the VR.

The regulator IGN ON wire is the B/w wire that comes from inside the dash harness and key. You should have 12V on that at the regulator with the key "on" only.

[JT68]

"My tests:
- the ballast resistor is present and wired, but I believe it to be gutted as I get battery voltage on both sides
- running a EI dizzy and blaster coil, though initially it was stock dizzy with capacitor and same coil
- with ignition in 'run', car not running, I get battery voltage
- with car running, I get -1 to -2-3v, varying slightly with rpm. Larger negative with higher rpm"

Jake, This is all normal-the resistor was not "gutted". There will not be a voltage drop across (any) resistor
unless there is current flowing through it.

When the car isn't running, there is no current, so the resistor shows no voltage drop.
When the car is running the average current through the resistor is varying with rpm. That is why the voltage drop varies.

The resistor is functioning normally.

[jake7140]

Never mind on the odd black wire; its the original neg dizzy wire! Duh. The EI dizzy has its own.

[Curtis]

On all roadster the black/white wire and the voltage regulator wires are on the same circuit but differ how they do it.
To 67.5 with original four fuse box. The coil wire is spliced to the wire coming off the ignition switch. The wire coming from the ignition switch goes to the fuse box. There the wire for the VR is hooked directly to the same terminal.

68. The VR wire is spliced to the same black/white wire coming off the ignition switch that goes to the fuse box and ballast resistor. After starting and running power goes to the VR.

The 68-70 have the ignition switch that first feeds the full 12v to the coil when cranking. This is the black/white wire with the red band. The black/white/red wire is spliced to the black/white/white wire. These wires may be yellow in a 70. After starting it sends power to the black/white wire with no color band hooked to the resistor.

70. The VR is fed on a fused circuit with the reverse, GVR and turn flasher power. This circuit is fed by the large black/white wire from the ignition switch. The black/white coil wire is connected inside the switch to this wire. So you still have an indirect connection to the coil wire and the VR. More wacky wiring from your friends at Datsun.

[jake7140]

Yikes. Thanks so much JT and Curtis!! I believe I get it mostly. I will have to reread to be sure, but sure does affirm that's some of the wiring is wacko from the factory. I always find it difficult to understand car wiring. I can understand a wiring diagram, but then translating to the physical harness can be difficult. Thanks to Curtis for filling I need that step on 311s. I am a bit slow, so it takes a couple tries, and then I forget anyway!

Still having difficulty wi voltage not regulating. Old style VR cranks out up to 17 volts at speed, 13 at idle. I got a new 1970 510 regulator, and that and that does not enable charging from the alt. I got a pin out for it and will match up pins on the car harness and the regulator plug. Suspecting something is out of place. Here's my translation: B=black

510 reg. STA. B+ B- L. FLD. Ign
Diagram. N. A. E. L. F. IG
Color. Y. W. B ? W/B. B/w

Sound right?

VR plug:

/ STA. B+. L. \
|
|. B- FLD. IGN |
|______________|

Seems L is the empty pin? On the color wiring diagram perhaps the black that goes to nothing? There is an L on the VR pinout and in the manual diagram of the VR, but not on the colored 68 diagram. THe manual diagram is difficult to read, but only 5 wires are labeled with color, and I assume that N is the yellow wire as there is N on VR and Alt. I think Curtis' diagrams have the plug pinouts. Will check.

I'll get my color-sighted mech asst to help me verify. Perhaps tomorrow. Will be interested to see for myself the behaviors described above and hopefully retain the functions of things.

Sorry, should prolly move this to a new topic.

Thanks again

[JT68]

I didn't check your pin positions, but L is for the alt light in a 510. No connection in a roadster. All the other colors typically match.

Yellow=neutral
white/blk=field
white=+12
black=ground (-batt)
black/white=ign on +12

17V is really not a big deal unless its always like that. (it probably isn't)
14-16V is more typical at rpm, but it will be higher if your battery requires charge
13 at idle is not off the mark

People get confused with these systems. They are not a "constant voltage" system. Voltage variations are
normal depending on the charge level of your battery and how much the alternator is putting out at a given moment.
The system is always trying to "top off" the battery.