What wires can be removed after LS swap?

[Ghost's68]

Hello everyone,

I just dropped my LS/4L80E into my 1968 SWB. I removed the bulk head from the firewall to look for the purple wire that goes to the starter. Unsure how PO wired it since the original wire was cut to about 8” and tucked into the wiring.

What wires can be completely removed? Truck has no AC and running a ModernVintage stand-alone harness.

Is there a wiring digram that shows an LS swap?

I removed all the tape and wire loom because I want to terminate any unneeded wires and to clean it all back up before putting it in. Any help is appreciated.

[Steve Cole]

I am curious about the same thing. I know you keep the starter wire, and I think the power wire to the alternator. Also if you are running original gauges, the water temp and oil pressure line. Aside from that, no idea. Good luck, I'm sure someone will have a definitive answer for you shortly.

['70_402]

I would think you'd need to keep the headlights, signals, starter, the "Main Power" wire, but if you're running aftermarket gauges, then the rest of that stuff can probably go away.

[Ghost's68]

Originally Posted by Steve Cole

I am curious about the same thing. I know you keep the starter wire, and I think the power wire to the alternator. Also if you are running original gauges, the water temp and oil pressure line. Aside from that, no idea. Good luck, I'm sure someone will have a definitive answer for you shortly.

Originally Posted by '70_402

I would think you'd need to keep the headlights, signals, starter, the "Main Power" wire, but if you're running aftermarket gauges, then the rest of that stuff can probably go away.

I wasn’t planning to delete the headlight/turnsignals lol. Just the other equipment the truck no longer has. Like the external voltage regulator and AC. How does one wire the alternator with LS swaps? I’ll be eventually going to Dakota gauges.

Also what about the inline fuse? Do I need to keep that? I pulled it apart and found the 4a fuse was shattered inside. I managed to pull it out though.

[davepl]

I'd look at a new M&H harness perhaps!

If I recall you basically need half. The one half is the forward lamp harness, and most all of it will be unchanged. The other half is the engine harness, and most of it will go.

You'll retain:

- Coolant gauge wire
- Solenoid (Crank) purple wire
- Ignition (12V) hot with no resistor wire

That's about it, so about three of that one side of the harness remain.

[Ghost's68]

Originally Posted by davepl

I'd look at a new M&H harness perhaps!

If I recall you basically need half. The one half is the forward lamp harness, and most all of it will be unchanged. The other half is the engine harness, and most of it will go.

You'll retain:

- Coolant gauge wire
- Solenoid (Crank) purple wire
- Ignition (12V) hot with no resistor wire

That's about it, so about three of that one side of the harness remain.

I will be replacing the harness also. I’ll have someone redo it since i have no experience with wiring.

Your saying I can remove that black with white stripe wire from the red hot? Do I
Terminate it at the plug and where it spliced into the red wire?



Also the red (hot) wire, one goes to the battery and the other goes to the external voltag regulator. What do I do about the one that goes to the regulator?

[Kennuck]

LT1swap.com has all the wiring pinouts for the LS Engine.
American Autowire has online wiring diagrams that can help you figure out the wiring of your truck.
You don't need the voltage regulator for an LS swap the alternator is internally regulated.

[Ghost's68]

Originally Posted by Kennuck

LT1swap.com has all the wiring pinouts for the LS Engine.
American Autowire has online wiring diagrams that can help you figure out the wiring of your truck.
You don't need the voltage regulator for an LS swap the alternator is internally regulated.

I have a harness made for the LS swap that is standalone. I just want to clean up the engine bay and eliminate any unneeded wiring. I removed the power to the AC unit since I no longer need that. I’m just unsure of everything else. Do I not need run any of these wires to the alternator?

[dec010974]

hello. i assume you are referring to truck wiring, right? if this is true, to be sure, i would get a wiring schematic for your truck. it will help you to identify what pins are used for the proper accessory. you can always double check by tracing the wire back to its source. i usually rewire truck with an aftermarket harness. Speedway motors makes a great gm universal harness for under 200 beans. i tried to do the same thing in my 1971 c10 and literally watched the ignition wire, the wire with the cloth, catch fire. good luck, clark.

[dec010974]

these may be helpful also (i am a wiring junky). the ones with the hook are the ones used in the fuse block bulk head. I may be thinking too much, but you may be able to reuse, modify, and build your old truck harness, bring it back to specs.

[Ghost's68]

Originally Posted by dec010974

hello. i assume you are referring to truck wiring, right? if this is true, to be sure, i would get a wiring schematic for your truck. it will help you to identify what pins are used for the proper accessory. you can always double check by tracing the wire back to its source. i usually rewire truck with an aftermarket harness. Speedway motors makes a great gm universal harness for under 200 beans. i tried to do the same thing in my 1971 c10 and literally watched the ignition wire, the wire with the cloth, catch fire. good luck, clark.

I have the wiring diagram saved on my ipad. Super helpful to determine what’s what. I will rewire the truck in the future but for now I just want to terminate all unecassary wires but do it safely so I can avoid situations such as yourself. I don’t want to have excess unused wiring balled up with electrical tape is all. If it can be removed, then out it goes lol

[Ghost's68]

I should be more clear, I only want to remove wiring that run in the engine bay, from bulk head to its connection. Ie. bulk head to external voltage regulator. Bulk head to oil pressure switch. Since it’s LS swapped I’m guessing I no longer need much of those wires.

[dec010974]

if you show me straight pictures i may be able to help identity some wires. i removed the original harness and have it laying in my truck. the first pic, (green wire) is for the horn. it goes to the ram style horn. i saw that you removed the extrenal regulator. i am running an 5.3/700r4. the pink wire is for +12v switched power. Red is for the +12V, which is connected to junction block. have you gave power to your engine yet? good luck.

[phat69]

Use the diagram above and trace every wire. It's the only way since we can not see you set up in person.

[VetteVet]

You had a 16 gauge brown wire from the bulkhead connector to the external voltage regulator. You need to run this wire to the LS alternator to the L terminal. The large red wire on the external voltage regulator plug needs to go to the S terminal on the LS alternator.

In the later models of CS alternators the brown wire was the only wire to the alternator. The voltage sensing and regulation is done by the PCM or the computer. If yours only had the single brown wire it is a 1996 or newer but since you don't have the PCM or computer you may need the red wire for voltage sensing

You will need to have a larger resistance in the brown wire than it has in the stock harness so you can wire an 80 to 300 ohm resistor in line with the brown wire before it connects to the L terminal. The 80 ohm resistor should be a 5 watt resistor and the higher resistance you go the lesser wattage you need. A 300 ohm resistor that's a 1/2 watt will work.

Here's a diagram.

[Ghost's68]

Originally Posted by dec010974

if you show me straight pictures i may be able to help identity some wires. i removed the original harness and have it laying in my truck. the first pic, (green wire) is for the horn. it goes to the ram style horn. i saw that you removed the extrenal regulator. i am running an 5.3/700r4. the pink wire is for +12v switched power. Red is for the +12V, which is connected to junction block. have you gave power to your engine yet? good luck.

Originally Posted by phat69

Use the diagram above and trace every wire. It's the only since we can not see you set up in person.

The wiring has been disconnected from the firewall and stripped of all the tape and loom. I’ll try and take a pic tomorrow of it.

Originally Posted by VetteVet

You had a 16 gauge brown wire from the bulkhead connector to the external voltage regulator. You need to run this wire to the LS alternator to the L terminal. The large red wire on the external voltage regulator plug needs to go to the S terminal on the LS alternator.

In the later models of CS alternators the brown wire was the only wire to the alternator. The voltage sensing and regulation is done by the PCM or the computer. If yours only had the single brown wire it is a 1996 or newer but since you don't have the PCM or computer you may need the red wire for voltage sensing

You will need to have a larger resistance in the brown wire than it has in the stock harness so you can wire an 80 to 300 ohm resistor in line with the brown wire before it connects to the L terminal. The 80 ohm resistor should be a 5 watt resistor and the higher resistance you go the lesser wattage you need. A 300 ohm resistor that's a 1/2 watt will work.

Here's a diagram.


Attachment 1763711

I have a LS3 from a Camaro and my standalone harness came with the plug for the alternator. I think it only had two pins. Does this change things? Also I won’t be using the factory gauges since I’ll be upgrading to the DD and run off of the OBD-2 for readings. Thanks for all the help so far guys. I’m trying to understand all this stuff the best I can.

[dec010974]

Hello vettevet. Can you explain? If he installed an LSx engine, and the pcm is doing the regulators job, why is he connecting all that stuff to L terminal and S terminal? I guess the original gauge cluster needs the S and L terminal, right? The LSx pcm, harness, and alternator should work without the external regulator. I don't want debate, I want this info for future reference. I do a lot of wiring and I don't recall doing it this way but you may be smarter than me. I don't qualify as the sharpest to tool in the shed.

[Ghost's68]

Originally Posted by dec010974

Hello vettevet. Can you explain? If he installed an LSx engine, and the pcm is doing the regulators job, why is he connecting all that stuff to L terminal and S terminal? I guess the original gauge cluster needs the S and L terminal, right? The LSx pcm, harness, and alternator should work without the external regulator. I don't want debate, I want this info for future reference. I do a lot of wiring and I don't recall doing it this way but you may be smarter than me. I don't qualify as the sharpest to tool in the shed.

That’s why I asked also.

[VetteVet]

Originally Posted by Ghost's68

That’s why I asked also.

The post I made was the conversion to The CS alternator for an engine without the PCM or ECM alternator controller which wouldn't have any way to regulate the alternator. It wasn't apparent whether the engine harness had any connections in the standalone harness for that. If it's there, then all that should be needed is to plug in the alternator control portion of the harness.

If it's an aftermarket harness then the manufacturer should have the answers .

We have an LS forum on the boards for swaps and I"m sure someone there has done this.

http://67-72chevytrucks.com/vboard/s...d.php?t=757024