240z/LS1 Electrical questions

[nocones]

I'm doing an LS1 swap into my 73 240z. I have the GM PCM reprogrammed and engine harness that I sent off to be modified with fuses and relays added for fans, fuel pump, etc. I should be set from this end. However, it is the Datsun electrical that I'm unsure of. I'm aware of the speedo and tach issues and have that figured out.

 

When I pull the stock engine, there will be wires for the alternator and starter hanging there. What do I need to do to make sure that all the interior electrical and lights still work when I'm done? Is it just a matter of connecting the old alternator and starter leads to the new alternator and starter?

 

Are there any other changes that need to be made to the stock system?

 

Is the stock voltage regulator still needed?

[ColtGT4g63]

I did not re-use any of the original battery cables for the starter or alternator. I ran a new wire from the alternator, to the starter. Then from the starter to the battery. From the battery, there were a few larger wires that power the inside of the car, I'm pretty sure I just put eyelets on them and connected them to the battery. I took the engine bay harness out of the car and weeded out the wires that i would not be needing. Such as voltage regulator wires, coolant temp / oil pressure sending unit wiring. You do not need to keep the original regulator. The pcm will take care of the LS1 alternator through the harness.

[nocones]

Let me start off by apologizing for my electrical ignorance. This is the one part of the swap that I feared the most.

 

Ok, just to make sure I have this straight. I should run a positive lead from the alternator to the starter and another positive lead from the same post on the starter to the positive battery terminal? Which wire gets connected to the little connector on the starter? I'm assuming this is where the wire from the ignition switch goes? What color is that wire?

 

And what about ground? I thought the original wiring had a ground wire running from the battery to the starter. The LS1 starter doesn't get a ground connection right? If not, what does the negative battery terminal get connected to?

 

To power the inside of the car, which wires get connected and what do they get connected to? It seems like if they are connected directly to the battery, they will always be on, even if the car is off.

 

Another related question: The stock 4 spd transmission had two sets of wires going to it. I think the rear one is for reverse lights, correct? What is the front set of wires for, the tachometer?

 

What is the best method of connecting the reverse lockout switch on the T56 to make that work?

 

Ok, that's all I can think of right now, my brain hurts!

[cheesepocket]

I feel your pain, having started with a '72 that was partially disassembled and not wired at all to the engine.

 

The big post at the starter is basically your junction for all the +12 VDC wires, that is the battery +, the alternator charging wire, and the input power to the fuse block and the rest of the body. The power wire for the fuse block on my car is a big white wire along the pass side wire harness run.

 

A great way to test this is to simply jumper the + side of the battery here at the big white wire, put - to the frame, and confirm your headlights turn on, etc. This will also power your "key on" wire that goes to what was your original coil, and the "start" wire that I pulled from the ballast resistor (get rid of the original ballast resistor, all power on the LS is 12 volts including engine run power, no need to drop down voltage for points ignition now). You need a test light or volt meter to confirm these wires.

 

You will have full-time power to the fuse block.

 

You should connect battery - to the engine block or head, and then use a ground strap between the engine and unibody frame to make sure all are on a common ground.

 

I would ordinarily recommend a factory service manual but mine was only marginally helpful as some of my wires were different colors than they should have been per the manual.

 

I have not messed with reverse lights and can't comment on those. Way down the priority list for me.

 

Last recommendation, go check out LS1tech.com for more LS wiring info, and Google search Datsun websites for Datsun body electrical info and explanation.

 

Good luck.

[m1noel]

You can use those same back up light wires with new connectors to the switch on the T56.

The reverse lockout is activated through the LS CPU and speed sensor, so if you are using the LS harness, it will just work. Just make sure when you go to hook up an electronic speedo or speedo drive, don't cut this wire. T-splice into it. I can't think of any wires going to the stock 4 speed except the back up lights. The tach comes from the distributor, not the trans. The speedo drive is a mechanical cable. It would really be best to get a wiring diagram for your particular year Z, and helpful to get one for the donor.

mike

[nocones]

Ok, I think that all makes sense. What/where is the ballast resistor? Is that the thing sitting below the coil?

 

I figured out the second set of wires going to the transmission is for the neutral switch. I have no idea what that is for and don't think I'll need these wires for the new setup.

 

Is there anything I have to do special with the wires that were running to the coil due to the way the tach and ignition is wired? From what I understand (which isn't very much) the tach is connected in series with the coil and ignition. I know when I previously disconnected my tach, the car wouldn't start. Now that the coil is gone, I'm guessing that the car won't start unless the series is completed somehow. Am I totally off base?

 

I also haven't been able to find a definitive answer to what the little box (relay?) is that is attached to the firewall right next to the battery?

 

Thank you guys for all the help. It is much appreciated. I'm sure I'll have more questions as things progress.

 

Believe me, I have been searching on google and LS1tech and haven't been able to find the answers to any of this. Probably not using the right keywords. Seems like there should be an electrical "how-to" for what wiring goes where when combining the LS1 system with the Datsun system.

[cheesepocket]

I spent some time in the garage last night working on the final wiring connections for mine. BRRRRRR!

On my '72, the wire that gives +12 VDC with the key on but not in the start position is black with white stripe. It should be bundled with the original ballast resistor wires, which I recall are green. I am editing my post above regarding the start wire. Use the original one that went to the Datsun starter solenoid, in my case it is black with yellow stripe. Again, applying + 12 VDC to the big white supply wire as described above will power your fusebox and chassis and allow you to test.

 

The neutral switch in the trans was part of the interlock circuit that would keep your 240 from starting if you were not in neutral, or if your seatbelt was not fastened. Lawyers, you know

 

You shouldn't sweat the existing wiring from the 240 too much. Most of these will be bypassed, capped off, and irrelevant since all the engine operation is handled separately by the GM powertrain control module.

 

I'll head back in the garage this afternoon and check my shop manual for '73 wiring to confirm the colors remained the same from my '72.

 

There were so many versions of the Datsun 240, 260 and 280 that no one wiring diagram would cover it. That's part of the DIY adventure and will give you that much more satisfaction when you have it running. That's what I keep telling myself.

[nocones]

On my '72, the wire that gives +12 VDC with the key on but not in the start position is black with white stripe. It should be bundled with the original ballast resistor wires, which I recall are green.

 

I found this wire, but what is it used for? The fuel injector relays get connected to switched 12v correct? But I was under the impression that you want the lead to them hot in the on position and in the start position. I've found other wires that are hot in both "on" and "start" like the fat white/red wire that used to go to the alternator.

 

Another thing I haven't quite figured out...I'm running wiring from pigtails on my T56 to the ECM since the tranny wires were mistakenly removed from the ECM plugs when the guy modified my wiring harness. In particular the skip shift solenoid and the reverse lockout solenoid. Both these pigtails on the transmission side have two wires. One of the wires from each goes to the red 44 and blue 79 pin but where does the second wire from each connector on the transmission go? Does it go to 12v or ground? Does it matter if the two wires on the pigtail are reversed? Since my pigtails aren't the same color as what the wiring diagram calls out, I don't know which wire is which.

[cheesepocket]

I can only report back in the context of the early, non-injected, 240Z.

The reason you want to find the bundle where the ballast resistor is that it is the location where key-on but not start signal is found. When your car is in the run position, the battery voltage is dropped to 6 volts or so by the ballast resistor to increase the life of the ignition points. When your key is in the start position, the ballast resistor is bypassed to improve starting performance, giving the points the full battery voltage. Apply voltage to the fusebox/chassis as described above on this thread, and use a test light or voltmeter to find the correct wire.

 

One choice on the T56 reverse lockout is to full remove the mechanism, then the lockout won't matter. Reverse is avoidable without the assistance of the PCM. As for skip shift, that should be removed along with rear O2 sensors, alarm, etc by whomever reprograms your PCM. If you have not had any reprogramming done on the PCM, I recommend it. Search the forums for discussion on who the good guys are out there to do it.

 

If you insist on these signals, hook up the two wires for both trans solenoids, use a battery to test, and you will find the correct polarity for these two. I don't know if that signal is switched to + voltage or ground in the PCM, so your best bet if you insist on having these connected is to test.

[nocones]

I can only report back in the context of the early, non-injected, 240Z.

The reason you want to find the bundle where the ballast resistor is that it is the location where key-on but not start signal is found. When your car is in the run position, the battery voltage is dropped to 6 volts or so by the ballast resistor to increase the life of the ignition points. When your key is in the start position, the ballast resistor is bypassed to improve starting performance, giving the points the full battery voltage. Apply voltage to the fusebox/chassis as described above on this thread, and use a test light or voltmeter to find the correct wire.

 

Ok, that makes sense but I think I am still misunderstanding something. For my LS-1 setup, why do I need this wire instead of one that is hot in both the "on" position and the "start" position? Is this what I should be using for my switched positive line? I believe the only switched positive connection I need to make is one that goes to the relays for the fuel pump, injectors, and radiator fans.

 

By the way, thanks for the tip of using the voltmeter with battery connected to the system to look for all the wires. Worked like a charm.

[cheesepocket]

Ok, that makes sense but I think I am still misunderstanding something. For my LS-1 setup, why do I need this wire instead of one that is hot in both the "on" position and the "start" position? Is this what I should be using for my switched positive line? I believe the only switched positive connection I need to make is one that goes to the relays for the fuel pump, injectors, and radiator fans.

 

By the way, thanks for the tip of using the voltmeter with battery connected to the system to look for all the wires. Worked like a charm.

 

Your PCM is only looking for two power sources: Battery power with ignition switch on, and continuous battery power. As far as I understand, your PCM doesn't need an external signal for the key in the start position. You can find your original wire that went to your Datsun starter solenoid, and connect directly to your LS starter solenoid with no modifications.

 

I believe your PCM knows you're cranking the engine because the reluctor wheel on the crank and also cam position sensor will be sending out pulses, then it knows to time the igntion and fuel in the right sequence. Once the engine fires, the rise in oil pressure is the indication that this has occurred, and the fuel pump will then run continuously.

 

Someone more knowledgable than me, feel free to jump in if I missed the mark here.

[nocones]

Alright, I've made some progress lately. Last night, I tried starting it and what do you know? It started right up on the first try. Then I tried turning it off and it kept running. Eventually pulled the power to the fuel pump to get it to turn off.

 

I think I found my problem but don't know how to fix it. When I originally tested my wiring for switched power, the fat white wire with red stripe (that was originally connected to the datsun alternator) was switched. So I connected everything up using this as my switched source. Now that I check it once everything is connected, it is getting continuous power which I assume has to be why the engine won't turn off.

 

Is this the wrong wire to connect for switched power or did I connect something wrong and give it continuous power?

 

What other wires are ok for switched power? will the wires that went to the coil/ballast resistor work even though they are hot in the on position but not in the start position?

[Aero Z]

I am also wondering what to do with this wire and am having trouble getting the non-LS1 systems on with the appropriate key position. What is done with ths WHITE/RED wire (and the black ALT wire) that originally went to the alternator? I have searched and seen some say you just need to power up that wire near the starter (which I have done but only the hazards and brake lights worked).

 

I have replaced all the Datsun gauges with Autometers so I'm not using the old ammeter gauge wiring. Do I need to connect/jumper the old ammeter gauge connections to complete that circuit (wiring diagram shows it runs through there)?

 

My car was originally a 73 auto.

 

Any help is appreciated.

 

 

I think I found my problem but don't know how to fix it. When I originally tested my wiring for switched power, the fat white wire with red stripe (that was originally connected to the datsun alternator) was switched. So I connected everything up using this as my switched source. Now that I check it once everything is connected, it is getting continuous power which I assume has to be why the engine won't turn off.

 

Is this the wrong wire to connect for switched power or did I connect something wrong and give it continuous power?

 

What other wires are ok for switched power? will the wires that went to the coil/ballast resistor work even though they are hot in the on position but not in the start position?

[nocones]

Your problem sounds like it is related to the ammeter gauge wiring. When you take that gauge out, you have to connect the two fat white wires together so that circuit is still complete, just as you suggest. I had the same problem and now all is good.

 

Good luck!

 

 

 

I am also wondering what to do with this wire and am having trouble getting the non-LS1 systems on with the appropriate key position. What is done with ths WHITE/RED wire (and the black ALT wire) that originally went to the alternator? I have searched and seen some say you just need to power up that wire near the starter (which I have done but only the hazards and brake lights worked).

 

I have replaced all the Datsun gauges with Autometers so I'm not using the old ammeter gauge wiring. Do I need to connect/jumper the old ammeter gauge connections to complete that circuit (wiring diagram shows it runs through there)?

 

My car was originally a 73 auto.

 

Any help is appreciated.

[Aero Z]

I did hook that up and all worked after I posted it to try it since I suspected that. By jumpering the old alternator wire I was

back wiring that circuit to everything downstream of the ammeter. Without it connected everything before the connection was hot.

Thanks for confirming. I also found a bad ground which was causing some other gauge weird problems.

 

Your problem sounds like it is related to the ammeter gauge wiring. When you take that gauge out, you have to connect the two fat white wires together so that circuit is still complete, just as you suggest. I had the same problem and now all is good.

 

Good luck!