1973 240z Custom Wiring From Scratch

[Matthew Abate]

Only 10A?

I’m thinking of splitting the 10 AWG white wire with a red stripe that comes from the alternator to the inside of the cabin. Originally it split off to the rear defroster and accessory relay, and terminated at the fuse box stud. The line going to the rear defroster had a 20A fuse on it originally.

The Koito H4 bulbs draw 10A each, and I’m retaining the long run of wires to the headlights that is in the engine harness to cut down on stuff outside of the cabin. Mainly I’m doing this relay mod to keep the power running through the combination switch as low as possible.

So what I’m thinking at the moment is splitting that 10 AWG white + red wire near the colored connectors and running it to the B post on the NLR-132. So there would still only be one wire coming off the alternator and feeding everything.

[SteveJ]

Are you keeping halogen bulbs? LED H4s will pull about 5A total from my measurements.

[Matthew Abate]

2 hours ago, SteveJ said:

Are you keeping halogen bulbs? LED H4s will pull about 5A total from my measurements.

Haven’t decided yet, but I want the option. I need to see how the LEDs perform before I commit, so if I don’t love them I would switch to H4.

[Matthew Abate]

Anyone have a source for the key warning buzzer and 3-wire door ajar switch for a 1973 240z?

I found a set but and hesitant due to price and unsure they even work.

I also have a workaround but am leaning OEM for now.

[Matthew Abate]

Can you guys help me figure out which relays I’m missing?

This is what I’ve found in my boxes:

1 - Horn Relay 26320-89905
2 - Defroster Relay 25230-N3000
3 - Thermostat Switch 22110-E8000
4 - Air Conditioner Relay 25230-89914 (the internet also says heater)
5 - Intermittent Relay 28820-N3300
6 - Fuel Pump Relay 25230-89915 (the internet also says headlight)
7 - Hazard Flasher (A & B not shown)
8 - Turn Signal Flasher
9 - Fuel Pump Relay 25235-P0101 (the internet also says fuse panel voltage regulator; I’ve seen a different relay with the same number)
10 - NLR-132 will be used for headlights

I have a key-warning buzzer coming in the mail for when the door is open and the key is in the on position. And I will not be using the Throttle Opener Relay that goes on the engine side of the firewall.

I have a 4-pin connector on the front fuel pump harness that I figure goes to a relay if you have an electric front fuel pump. I’m keeping my mechanical one for now because it is NOS. If it gives me issues I’ll switch over. I am assuming not having this connected doesn’t mess with anything since that was stashed away with blue tape from the factory.

I’ve also seen things about a “heater / choke” relay, but don’t see anything for that in the diagram. I found a relay numbered 25235-P0110 on a Datsun 1200 wiki, but can’t find anything for Z cars.

—-

I think I’m all set. I don’t think I need to retain the thermostat switch (#3). I think this might be unique to 1973-4 automatics.

Can anyone identify that thing or think of anything I might be missing?

Edited March 18, 2024 by Matthew Abate

[Matthew Abate]

I’m not 100% certain all of these relays are good (still testing), but I cleaned up the best looking pieces from my pile assembled them today. 🤞🏻

[Matthew Abate]

I’m hoping someone can clarify some things for me:

I would like to put something approximating the “correct” capacitor (aka condenser) on my coil and wire it up as original if possible.

Z Car Depot describes the RFI suppression capacitor as plugging into the harness via a bullet connector.

My harness was cut at several points because the previous owner was trying to force an AT harness to work in a manual, so I may have made a mistake when mapping everything to the wiring diagram.

There is a B/W wire that splices to a green wire that ran to the voltage regulator and then through the firewall and to the green wires coming off the fuse box that supply power to the seatbelt switches & light and gauges.

Could this B/W wire be what is supposed to connect to the capacitor? If so, that makes it easy. If not, I’ll just use it as an aux power feed and tape it back for any future needs.

Secondly, is that even the best way to wire it up? I know others wire it directly to the positive pole on the coil.

And last, does it matter what capacitance rating I use for this? The 280ZX (my engine and ignition are from a ZX) used a two-wire, 250v, .47uF capacitor. I have no idea what the 240z used. As far as I can tell, the .22uF ones were for the dizzy.

I’ve found one from an RX-7 that has that rating, but it doesn’t look anything like the cylindrical ones from the ‘70s. I’ve also found some that are .50uF. Is that difference going to impact anything?

Maybe this is trivial and I’m overthinking it, but like I said, I’d like to at least try to get it right.

Edited May 24, 2024 by Matthew Abate

[Matthew Abate]

Heyo! Who ordered deez spaghetts?

All of the dash components are wired up except for reinstalling the old rheostat (more on that later). After I do that, the next step is to put the dash into the car and terminate the wires you see hanging out on the ends. Those go to the fuse box, AC, multi switches, relays, and other harnesses.

I decided to pull the home-made PWM setup I had and reinstall the OEM rheostat, because I found a nice little PWM unit meant for a Porsche 928 called an AILD-1 that’s controlled by an old-school rheostat instead of using a pot installed directly on the circuit board.

I haven’t figured out where it’s going to mount yet, so I’ll make a harness that inserts the AILD-1 between the rheostat and the dash harness but keeps the original terminals. That way if for some reason I decide to go back to incandescent bulbs I can just pull the PWM and connect everything as stock.

Edited January 8 by Matthew Abate

[Matthew Abate]

So close! I have three steps left before I can wrap these dash harnesses and put them into the dashboard for real: installing and wiring my NLR-132 headlight relay, installing and wiring the AILD-1 PWM, and testing everything.

I can test everything except the dash lights and headlights now, so I’ll probably wait on the relay and PWM because I’m not certain where I want to put them yet.

This was not crazy hard, but it did take four or five times as long as I estimated, plus my body is killing me from laying on the seat rail braces. These cars are not spacious.

I kept up my system of labeling the terminals with what’s on the opposite end of the wire, so if I do discover any issues they should be fairly easy to diagnose. I checked all of these wires so many times I can’t imagine I have any errors, but who knows.

¯\_(ツ)_/¯

I’m having some trouble with terminals staying in the colored connectors I scavenged from the old harness. I guess I mangled them too much getting them apart. I’ll see if I can fix that when I pull the harnesses to wrap them.

For a minute I couldn’t figure out where to mount the buzzer.

I ended up using a threaded hole on the left side of the dashboard frame.

The buzzer looks like it’s supposed to be there, based on the way the bracket is bent, but I have no idea if it’s correct. I think those holes were fire the heater or stereo originally. Whatever. It works.

Edited January 26 by Matthew Abate

[Matthew Abate]

Well, I found my first problem, but it’s not with the wiring.

I have the NLR-132 dual relay installed and partially wired. With the combo switch connected to the harness I hear a click in the relay as soon as I connect the battery.

When I unplug the combo switch there is no click when I connect the battery.

So it seems the fault is in the combo switch, but I’m going to disconnect each of the signal wires to see which one is tripping the switch in order to narrow down the problem.

One question I have is should the lights should work with the key off? If not then I have another error somewhere. If so I might change that.

Edited January 26 by Matthew Abate

[SteveJ]

I'm not exactly sure how you wired it, but I think it should be something like this. (See below. It looks right.)

S - 12VDC+ (This should be the R or RY wire from the fuse box)

S1 -  low beam ground at combo switch

S2 - high beam ground at combo switch

B - 12VDC+ fused

L1 - low beam positive

L2 - high beam positive

 

Now, I took another look. It seems like that is how you wired it. So, I would disconnect the battery and look for continuity between the S & B terminals with your wires landed. If it is, then disconnect the WR or R wire and test again. If the relay checks out fine, move to the combo switch. Just my 2 cents.

[Matthew Abate]

Thanks!

So to say it back to makes sure I understand, with the battery disconnected and the wires on the relay, if I get continuity then it’s either the relay, combo switch, or wiring. If there’s continuity without the wires it’s the relay; no continuity it’s the combo switch or wires.

If, after all that, I unplug the combo switch and get continuity between the two signal wires at the combo switch connector on the harness, it’s the wiring.

Conversely, if I get continuity between the wires coming from 15 & 16 on the combo switch while it’s set to OFF , it’s the switch.

Clearly I’m too tired as this seems obvious now that you said it.

Edited January 27 by Matthew Abate