1973 240z Custom Wiring From Scratch

[SteveJ]

I have mounted relays for headlights on the driver's side of the center stack for my relay solution that isn't visible to the casual observer. If you are trying to be very compact you could try a relay like this: https://www.amazon.com/gp/product/B08DD5FRSW

The pros:

1. Fuses for the loads are at the relay.
2. This is more compact than two separate relays.

The cons:

1. I have no long-term experience with this relay.
2. You have to replace the whole unit if a relay goes bad.

[Matthew Abate]

I’ve seen relays like this in some build threads for various domestic cars I’ve seen around. Could be a good way to go.

At the moment I am considering putting my relays in the space where my radio used to be. I was planning to have a box there for my phone but I might be able to do both.

Edit: It seems that there are many manufacturers of the NLR-132, but I think the original (and probably best quality) was made by New Era for the JDM. I see a few floating around obscure corners of the internet but nothing easy to acquire without an importer in Japan.

Edited July 28, 2023 by Matthew Abate

[Matthew Abate]

Made some good progress on the engine harness today. Im hoping I’ll get that done this weekend.

Deleting the circuits for the voltage regulator and the throttle opener and all of the related bits freed up a fair number of terminals in the colored connectors. I contemplated consolidating them but decided against it. Better to stick with the factory positions for each wire, even though I made my own diagram and labeled everything.

I also decided to hard wire the fuel pump A and B harnesses into the engine and dash harnesses rather than have so many connectors. With the increased wire gauge, AC, and extra relays under the dash I need all the space I can get.

No pictures today. It just looks like piles of wire right now.

Oh, by the way, @SteveJ, does that relay you posted need anything special due to the negative switching on the headlights? I read somewhere that it has a common ground on the signal circuits, which makes me think it would have to be wired differently than it may be design to be wired.

Edited July 28, 2023 by Matthew Abate

[SteveJ]

What I did was make harnesses to intercept the wiring in the headlight circuit. At the high/low beam switch the RB and RW wire from the switch are routed to the 86 pins on the relays whereas the RB and RW wires from the dash harness are connected to the 30 pins on the relays. The R and RY wires from the fuse box are routed to the on the 85 pins on the relays. The R and RY wires in the dash harness are grounded. I landed a wire on the stud on the bottom side of the fusebox to go to fuses and on to the 87 pins on the relays.  The terminals I used are for Bosch relays.

Here's a picture of the other relay.

The terminals are 

S - Signal Common

S1 - Low Signal

S2 - High Signal

B - Battery

L1 - Low Beam to Headlight

L2 - High Beam to Headlight

You would only need one wire from the fusebox (either R or RY) to the S terminal. You would bring the RB and RW wires from the high/low beam switch to S1 and S2. The power wire from the stud in the fusebox would go to B. The RB and RW wires from the dash harness would go to the L1 and L2 terminals.

It would be easier to understand if I drew it out, but that would be for another time.

[Matthew Abate]

3 hours ago, SteveJ said:

It would be easier to understand if I drew it out, but that would be for another time.

I took a stab at it:

Edited July 28, 2023 by Matthew Abate

[SteveJ]

Just a minor clarification:

Also the R and R/Y wires in the dash harness no longer connect to the fuse box. They are grounded.

[Matthew Abate]

I was wondering if I had the light wires backwards.

[SteveJ]

As long as S1 and L1 line up color-wise, your high and low beams will be correct.

[Matthew Abate]

Okay, I have a real dumb question, but seeing as my car was not put together when I bought it and I can’t find photos of this, I feel like I can ask anyway…

How are the wires connecting the engine harness to the headlights routed?

I don’t see any holes forward of the radiator support that go to the area behind the headlight bucket. The only thing I can figure is they go under the frame and then back up u set the fender, but this seem awe fully exposed to the elements.

If someone could take some photos of the correct routing I would appreciate it.

Edited August 7, 2023 by Matthew Abate

[billgtp]

they route under the headlight buckets. this should help

[Matthew Abate]

 

Finally.

The engine harness took me forever for a number of reason, but the main one being my earlier indecision on electric fans. I spent a ton of time trying to figure out where to put the relays (and the AC drier) in the car and how to protect them from the elements, only to realize that I am better off sticking with the mechanical fan for my purposes.

Hear me out…

1. From what I’ve been able to find on the internet, the mechanical fan draws somewhere around 3,400 CFM at cruising RPM when below speeds that the fan clutch disengages and lets it freewheel. The best drawing electric setup I could find was two 12” High Output Spal fans that, together, would get me 3,740 CFM at optimal conditions. That’s great but they pulled 100 amps EACH when they start and 40 amps each when they run. The next best (strongest) option without the electrical consumption issue produced 3280 CFM. When I make changes  I’m looking for better than stock.

2. If the mechanical fan really only saps 3-5 horsepower, then the simplicity, lower cost, and reduced wiring is more desirable than that gain. Yes I have a 100 amp alternator, but I don’t want to tax it more that I need to.

3. I am not a fan of the radiator shroud options for electrics. Anything that isn’t just a flat sheet reduces the clearance between the fan and the engine because the fans are all surface mounted. The mechanical fan protrudes into the old school shroud, and I can get a fiberglass replica at MSA. I did find an OEM metal one but it has been cut in two places and I think the guy wants too much for it.

However, the reason I kept going back and forth was I do like that electric fans can pass more air over the radiator at a stand still than the mechanical one because they are governed by the engine temperature rather than the engine speed. I figure that I can always put a 1630 CFM pusher fan on the AC condenser if I start having issues later, or I can always change this later if I have issues.

The engine harness is together, I have the connectors on the interior side, and now I can go on to adjusting the positions of zip ties that set up the the harness branches, which I hope to have done by a week from now.

@billgtp, thanks for the photos! That was super helpful

Edited August 14, 2023 by Matthew Abate

[Matthew Abate]

One complete (mostly) engine harness.

Mostly because I am waiting for a handful of connectors to come in the mail. Once those are on I can instal it.

I opted to wrap the harness in Tessa tape sealed with adhesive shrink tubing rather than use split loom or whatever. I think the taped look suits the car better and I’ve made provisions for anything I might add to the car that would need to tie into this (electric fuel pump).

I used 51608 PET Felt tape on the end that is inside of the car to cut back on rattling or any other noises this could cause, but the rest of it is wrapped in 51036 PET Cloth Flame Retardant tape (their high heat  chemical resistant stuff).

As I was wrapping it up I realized that I had forgotten to put the diode on the Lamp wire to the alternator, so I had to splice that in.

 

Looks okay. Good thing it’s wrapped up.

I can’t remember if I mentioned this, but I opted not to splice the ballast resistor wires. Instead I made the stubby and put bullet connectors on them so the can be connected (I’m going to make a nicer looking jumper later). The reason is so if I discover that I do in fact need the 2,200 ohm resistor to make my tach work correctly with the e12-80 I won’t have to cut the harness open and can just pop it in there.

And finally just a couple of shots of how I branched the wires prior to wrapping  the harness.

 

Changes from factory:

• Ballast Resistor delete
• AC pressure switch & compressor power
• Integrated electric fuel pump wiring (rather than separate harness)
• Ground wire direct to battery (-)
• 4-wire setup for 100 amp GM-style alternator

Edited August 28, 2023 by Matthew Abate