LS Engine Wiring Guide

[Built6spdMCSS]

If it needs switched 12v sounds like you can run it to that pink wire, however there is NOT a fuse on that pink wire anywhere so put one inline before splicing into that MSD Box.

Basically splice in one of them 10ga or 12ga inline fuse holders and put the 30A in it.

 

[RabbitHoleSS]

Looks like you just run it off a relay.
So run a 10ga wire off the + starter post to an inline fuse. Then follow the msd directions from there.
Your new wire goes to 30. Pink wire from the old dizzy goes to 86. 85 is ground. 87 feeds the msd box.

 

[Built6spdMCSS]

That Pink Ignition wire is large enough to support the amperage why I suggested what I did, avoids needing a relay with the extra wiring.

 

[Cams85GP]

Man, I really appreciate you guys responding, definitely helping.

So if I go with a relay,I’ll need 10ga for starter post wire and ground? I only ask because the MSD wire is noticeably smaller than the pink ignition wire, if that matters. I swear I try and find this stuff online, but can’t find anything specific enough for us LS newbs.

And once the ignition is figured out,along with starter/alt wires, all other under hood wires are garbage,? other than choke wire, since I’ll be using aftermarket oil press, volt, coolant gauges. Clutch fan,no AC.

I’m so close to firing this thing up, and I go and break my wrist, 7 screws and a plate later, it’s really slowed down the last little things.

 

[Built6spdMCSS]

If that red wire is smaller than the pink wire on the car I stand behind what I said even more, with an inline fuse. No need to complicate it.

 

[RabbitHoleSS]

I only advised 10 ga wire because your instructions call for a 30 amp inline fuse and relay to be used. But if the wire is smaller on the box, I don't really see the need for any of it.
The alternator exciter wire needs a 194 bulb put in line, or a 470ohm resistor.
This goes to the L post on your alternator.
If you wanted, you could run the exciter wire from the alt charging post with that resistor inline straight to the L terminal.
And no all the other wires aren't garbage, they can be repurposed to build circuits Like mentioned.
Reread the beginning of this sticky, Built6spdMCSS tells you every wire you need to keep installed in the car.
Also click the lt1swap.com link he provided and read, it also has easy to understand info.

 

[Built6spdMCSS]

Yup the pink wire into one of these inline fuse holders then to the red wire on the box will be fine.

 

[OGcutdawg_83]

Hello, just jacking a thread. I have a ls swap cutlass, my battery isn’t charging I bought a plug and play 4 wire to 2 wire harness. My question is, is the brown wire just a signal wire for the dash or is it 12v switched. Pretty much need help wiring the alternator to charge. This is what I have. The brown wire is going to the L terminal and D terminal is on the back post on the alternator.

 

[PAPERGATOR$]

I'm gonna post this up so it may help some people.

Bunch of LS Engine Wiring Harness schematics here:

Wiring Harness Information

Here is the diagram for the Gbody Firewall Bulkhead Connector:

View attachment 216515

I posted the link for the schematics in reference to what some people may have as "standalone harnesses" or you build your own, can use the schematics to double check what you have.

The wiring on the Firewall Bulkhead is simple:

Two 12ga RED wires are 12v battery wires coming in off the battery POS cable at the starter, they have fuseable links on them. These both go into the ignition switch on the column.

Single 12ga PURPLE wire is from the ignition switch on the column to the starter solonoid to start the car.

Single 12ga PINK wire is the 12v Key-on Ignition wire to the Distributor.

Mentioning them above because they are important. The rest are labeled as such. Leave the lights and horn wiring alone.

EFI LS Swap is simple.

Keep the two RED going into the Firewall powered from battery POS 12v. They do not have to be connected to the starter if you install a fuse box that connects to the battery, and has outputs that are constant battery power. 12v battery outputs on the fuse box can be spliced to these two wires going to the Firewall. Would be wise to have a fuse on them somewhere if the fuse box doesn't.

PURPLE 12ga needs to stay from the Firewall Bulkhead going to the little peg on the starter solonoid.

PINK 12ga wire gets connected into any circuit that needs 12v key-on ignition power.

All the wiring that is connected in the existing SBC/V6 Engine Harness can be clipped and re-purposed since you're installing the LS EFI Harness.

I used that wiring and built several circuits that I needed depending on how I ran wires.

I make it sound simple, there not much to it as long as you understand a wire has two ends. The rest is up to you how you want to do it.

I installed the whole fuse box out of a 1998 Camaro into my SS, spliced in the fuse box into the existing factory Gbody firewall bulkhead wiring. Since it was a GM fuse box all the colors matched. 4ga wire from the battery ties into the fuse box to give it 12v, from there I connected the two RED 12ga wires going into the firewall bulkhead. PINK 12ga coming out connects to the Pink wire on the fuse box 12v key-on Ignition circuits. PURPLE 12ga goes to the Starter through the engine harness. My LS engine harness plugs into the fuse box portion that connects to the wiring for the LS Engine & PCM. I also have a connector inside of the car to run the gauges and to the OBDII DLC.

That's pretty much it. 👍

I have a 81 Caballero 3.8 L V6 and there’s no power wires running to or from the fuse box. How can I add a power wire to the fuse box? I was able to label the starter, distributor, oil pressure, coolant and alternator wires before I pulled the engine so I’m not worried about them wires.

 

[Built6spdMCSS]

I have a 81 Caballero 3.8 L V6 and there’s no power wires running to or from the fuse box. How can I add a power wire to the fuse box? I was able to label the starter, distributor, oil pressure, coolant and alternator wires before I pulled the engine so I’m not worried about them wires.

Which fuse box are you talking about?