1973 240z Custom Wiring From Scratch

[Matthew Abate]

I've made major progress on my wiring diagram. I didn't finish the fuel harness for the rear of the car because I don't have one handy, but I don't think it is that important for moving forward. I do have a handful of mysteries, though. I think they are mostly caused by my having an engine harness for an automatic, but I am not sure. I will try comparing the two wiring diagrams in the morning.

In the mean time, maybe someone knows the answers…

1. On the two blue 10-pin connectors that join the dashboard harness to the engine harness, I have a Black wire with a Yellow stripe missing from both sides. It's in the FSM on pages BE-2 and BE-3 but the only thing I am seeing in the actual diagram (page BE-5) is the Black wire with a Yellow stripe that goes to the water tank. In my harness that wire is actually Black with a White stripe, and most of the Black wires with a Yellow stripe are related to the seatbelt relay, the throttle opener, and the thermo relay.

 

2. On my engine harness I have a Black wire that has been cut, which I have labeled "battery ground?" in the drawing below, but that probably isn't right. It comes out of the main trunk of the harness near the seatbelt relay for the automatic car and runs back to the green 10-pin connector that joins the dashboard harness to the engine harness. That wire is completely missing on the dashboard side.

 

3. I have three cut wires and a missing wire that I am pretty sure are related to the thermo switch and the throttle opener, but I want to be entirely sure.

I am pretty certain that the Black wire with a Yellow stripe, which has been cut, goes to the throttle opener. The Green and Black wires, also cut, branch from the main trunk of the harness at the same point as the Black wire with a Yellow stripe, near the distributor in the front left corner of the engine bay. On the other end, the Green wire connects to the Voltage Regulator, the Distributor Condenser, and ultimately the fuel pump in the back of the car. The Black wire connects to all of the other black wires in the Engine Harness going to the lights, Alternator, Starter, and the Intermittent Relay. In retrospect, I think these two wires go to the Thermo Switch and control the EGR vacuum control.

The missing one is the Green wire with a Black stripe, which could be one of the other three and is just mislabeled in the FSM, or could be entirely missing. I'm pretty sure it's missing because there should be a GB wire going to the green 10-pin connector that connects to the dashboard harness in the pin highlighted with the red circle below. This GB wire would connect to the Yellow wire with a Red stripe on the dashboard harness, which we have previously discussed as being for the throttle opener. In the FSM this is shown going to the Relay Assembly Type K24 (Throttle Opener Relay), but on the manual cars.

 

4. I have three items in the FSM wiring diagram that I am missing in my own because I don't have any connectors remaining to identify. Here's what's in the FSM:

• Solenoid Valve Assembly (EGR Vacuum Control) - Different from the Throttle Opener Vacuum Control
• Thermo Switch Assembly (Temp Sending Switch) - This is probably two of the cut wires above
• Relay Assembly Type K5 (Distributor Relay) - Possibly unimportant since I am switching to an e12-80
• Inhibitor Switch - Possibly what I have labeled as the Seatbelt Relay, which is what the FSM has that connector labeled on page BE-2

Edited February 2, 2023 by Matthew Abate

[Matthew Abate]

Next to last step (other than identifying those damned cut wires) is to map the relays to the harnesses, so I went through my pile o' parts and this is what I have:

Voltage Regulator #1 - Elecman HBA12-2 by F.D. Japan, 6 wires (Y, W, WR, BW, WB, and

 

Voltage Regulator #2 - Product HBA12-2 by F.D. Japan, 6 wires (Y, W, WR, BW, WB, and

 

Electric Fuel Pump Relay - HR1-14 12v 706 (PN 25235 P0101) by Hitachi

 

Ballast Resistor - RC-15 by Hanshin

 

Two different distributor condensers - The longer one is a NC-47CT-A2 150v 47m capacitor by NCC. The other is illegible.

 

The front of my relay bundle - Clockwise from bottom:

• Windshield Wiper Relay by Jideco (PN 28820-N3300)
• 3-pin 12v 15A Horn Relay by Miyanmoto Japan
• 4-pin Defroster Relay
• 6-pin Fuel Pump Relay by Jideco (PN 25230 89915)
• 3-pin MR2-101 Accessory Relay by Jideco (PN 25230 39914)

 

The rear of my relay bundle has a HF546A 12v Heavy Duty Flasher Relay by Niles

 

And another 6 pin relay with no markings by Jideco. Could be a Choke or Headlight Relay, or another Fuel Pump Relay as above.

Edited February 3, 2023 by Matthew Abate

[Matthew Abate]

I'm almost certain the G and B wires are for the Thermostat Relay. The FSM indicates there should be 2 B wires and an RB wire as well, which come off the distributor and the distributor relay. I am missing that connector in my AT harness, so that has to be it. Here it is illustrated on page BE-2 of the FSM:

Edited February 2, 2023 by Matthew Abate

[Matthew Abate]

I unearthed another box of wiring harnesses I had buried in my basement which has shed light on some things above, specifically the Fuel Pump Relay and how that fits into the rest of things. This thread started by @conedodger prompted me to look for the harnesses that were added in late 1973 shown in the illustration below supplied by @Carl Beck:

On 9/11/2012 at 11:46 AM, Carl Beck said:

So here's what I found:

Clockwise from far right, they are…

• Fuel Pump Harness A (PN 24032-N3300)
• Electric Fuel Pump & Fuel Sender Unit Harness (PN 24815 E8200)
• Fuel Pump Harness B (PN 24034 N3300)
• Fan Blower Switch Harness (PN 27155 E4400)
• Climate Control Face Harness (PN 24026 N3300)

So it looks like the one thing I am missing is Relay A (PN 25235 P0100) from the illustration @Carl Beck provided, which I have seen labeled as a heater relay or an Auto Choke Relay, but seems NLA like all the others.

Should be fun trying to scrounge this, but first I need to add these 5 harnesses to my diagram and spreadsheets.

Edited February 4, 2023 by Matthew Abate

[Matthew Abate]

Someone asked me why I’m making all new harnesses from scratch rather than rebuilding what I have, and I think these photos answer that question. I have problems like these throughout all of my wiring across the entire car:

Edited February 6, 2023 by Matthew Abate

[240dkw]

On 2/2/2023 at 8:00 AM, Matthew Abate said:

Two different distributor condensers - The longer one is a NC-47CT-A2 150v 47m capacitor by NCC. The other is illegible.

There are three condensers on the car, one on the distributor for the points and two for noise suppression. One connects to a male spade on the positive post of the coil and is grounded using the ballast resistor mounting bolt. The other one goes on the alternator + and -. Don’t buy the cheap ones from places like Rock Auto. None of the ones I bought lasted for more than a couple of hours. Napa has quality ones built in Mexico.

[Barefootdan]

2 hours ago, Matthew Abate said:

Someone asked me why I’m making all new harnesses from scratch rather than rebuilding what I have, and I think these photos answer that question. I have problems like these throughout all of my wiring across the entire car:

Nothing quite as good as something brand new! You also gain immense knowledge of your wiring circuits. Countless times I have ran into an electrical mishap (be it my fault or a faulty part) and I can still think back to when I did my wiring harness to diagnose the issue without the need for diagrams. 

[Matthew Abate]

11 hours ago, 240dkw said:

There are three condensers on the car, one on the distributor for the points and two for noise suppression. One connects to a male spade on the positive post of the coil and is grounded using the ballast resistor mounting bolt. The other one goes on the alternator + and -. Don’t buy the cheap ones from places like Rock Auto. None of the ones I bought lasted for more than a couple of hours. Napa has quality ones built in Mexico.

Thanks! I’m going to delete the points and move to electronic ignition, but good to know about the others.

In a quick google search I’m seeing a coil condenser and a voltage regulator condenser. Are these the other two, or is the coil condenser the same as the distributor condenser?

I’m also seeing one for automatic transmissions.

Edited February 7, 2023 by Matthew Abate

[SteveJ]

Coil = Ignition Coil

The coil condenser should be attached to the positive terminal of the coil.

The condensers for the charging circuit are not documented in the 240Z wiring diagrams. The 260Z is the first that shows them. There is one on the WR (main) wire and another on the BW wire before the VR.

[Matthew Abate]

Thanks for the additional details!

Here are a couple more tables…

1973 240z Fuel Pump Harness A (24032-N3300) Inventory
Position	Component	Connector Color	Connector Style	Direction	# of Pins	# of Wires	Sample Wire Color	Min. Feet of Wire Needed	Wire Gauge
1	Engine Harness	White	Nylon	Male	6	5	Yellow	[See Voltage Regulator]	14 AWG
							Yellow	[See Voltage Regulator]	14 AWG
							–	[See Voltage Regulator]	14 AWG
							Black w/ White	[See Voltage Regulator]	14 AWG
							Yellow w/ Black	[See Voltage Regulator]	14 AWG
							Black	[See Voltage Regulator]	14 AWG
2	Voltage Regulator	White	Nylon	Female	6	5	Black	1 (from Engine Harness)	14 AWG
							Yellow w/ Black	1 (from Engine Harness)	14 AWG
							Black w/ White	1 (from Engine Harness)	14 AWG
							–	–	–
							Yellow	1 (from Engine Harness)	14 AWG
							Yellow	1 (from Engine Harness)	14 AWG
								[See Fuel Pump Junction B]	14 AWG
3	Fuel Pump	Clear	Spade	Female	1	1	Black w/ Yellow	[See Fuel Pump Junction A]	14 AWG
4	Fuel Pump Junction A	Clear	Spade	Female	1	1	Black w/ Yellow	4 (from Voltage Regulator)	14 AWG
5	Fuel Pump Junction B	Clear	Bullet	Female	1	1	Yellow	3 (from Fuel Pump)	14 AWG

 

1973 240z Fuel Pump Harness B (24034-N3300) Inventory
Position	Component	Connector Color	Connector Style	Direction	# of Pins	# of Wires	Sample Wire Color	Min. Feet of Wire Needed	Wire Gauge
1	Dashboard Harness	White	Nylon	Male	2	2	Green	[See Fuel Pump Relay]	12 AWG
							Black w/ White	[See Fuse Loop]	12 AWG
2	Fuse Loop	White	Nylon	Female	2	2	Green	[See Heater / Choke Relay]	12 AWG
							Black w/ White	1 (from Dashboard Harness)	12 AWG
3	Fuel Harness B	White	Nylon	Male	2	2	Green	[See 20 Amp Fuse]	12 AWG
							Black w/ White	[See 20 Amp Fuse]	12 AWG
4	20 Amp Fuse	White	Nylon	N/A	2	2	Green	1 (from Fuel Harness B)	12 AWG
							Black w/ White	1 (from Fuel Harness B)	12 AWG
5	Fuel Pump Relay	White	Nylon	Female	6	5	–	–	–
							–	–	–
							Black w/ White	[See Fuel Pump Junction A]	12 AWG
							Green	[See Heater / Choke Relay]	12 AWG
							Green	5 (from Dashboard Harness)	12 AWG
							Black	[See Heater / Choke Relay]	14 AWG
								[See Ground]	14 AWG
6	Ground	Black	Ring	N/A	1	1	Black	1 (from Fuel Pump Relay)
7	Heater / Choke Relay				4	4	Green	5 (from Fuse Loop)	12 AWG
							Yellow	[See Fuel Pump Junction B]	12 AWG
							Black	1 (from Fuel Pump Relay)	14 AWG
							Green	1 (from Fuel Pump Relay)	12 AWG
8	Fuel Pump Junction A	Clear	Spade	Male	1	1	Black w/ White	2 (from Fuel Pump Relay)	12 AWG
9	Fuel Pump Junction B	Clear	Bullet	Male	1	1	Yellow	2 (from Heater / Choke Relay)	12 AWG

Edited February 7, 2023 by Matthew Abate

[Matthew Abate]

This whole exercise has been a series of forehead slapping moments. Today was another one, where I realized that the bullet connectors making a junction on the fuel sending unit harness are there for connecting a fuel pump, which explains why there is no connector for said fuel pump. Mine doesn't have this, but there should be blue tape holding them down, which we all know by now is the giant beacon Nissan supplied for all optional components:

(Image Source)

I went round and round on this, but then I realized that the blue tape meant "optional" so the corroded bullet connectors in my post from yesterday had to be the way they meant for us to connect an electric fuel pump.

Anyway, here's the table for it:

1973 240z Electric Fuel Pump & Fuel Sender Unit Harness (24815-E8200) Inventory
Position	Component	Connector Color	Connector Style	Direction	# of Pins	# of Wires	Sample Wire Color	Min. Feet of Wire Needed	Wire Gauge
1	Body Harness A	White	Nylon	Male	2	2	Black	[See Yellow Splice A]	14 AWG
							Yellow	[See Sending Unit]	14 AWG
2	Body Harness B	White	Nylon	Male	1	1	Green	[See Fuel Pump]	12 AWG
3	Chassis Ground	Black	Ring	N/A	1	1	Black	[See Yellow Splice A]	12 AWG
4	Yellow Splice A	N/A	N/A	N/A	3			1 (from Body Harness A)	14 AWG
								1 (from Chassis Ground)	12 AWG
								[See Yellow Splice B]	12 AWG
4	Yellow Splice B	N/A	N/A	N/A	3			2 (from Yellow Splice A)	12 AWG
								[See Fuel Pump]	12 AWG
								[See Sending Unit]	14 AWG
6	Fuel Pump	Clear	Bullet	Male	1	1	Black	1 (from Yellow Splice B)	12 AWG
		Clear	Bullet	Female	1	1	Green	3 (from Body Harness B )	12 AWG
7	Sending Unit	Black	Ring	N/A	1	1	Yellow	3 (from Body Harness A)	12 AWG
		Black	Ring	N/A	1	1	Black	1 (from Yellow Splice B)	14 AWG

Edited February 7, 2023 by Matthew Abate

[Barefootdan]

I may have missed it, but is there a reason to do this in the car rather than pulling everything out? Just curious 🙂