Body harness wiring

[Ghost's68]

What’s up everyone!

I posted this question up under general but I wasn’t able to get the answers I needed, so I’m posting it on the swap forum.

So I got a LS3 and 4l80e swapped into my 68. For the engine I’m running a Modern Vintage stand-alone harness. I pulled my bulk head off the firewall and want to clean up the wiring.

There’s a top part and bottom part. It appears the top section, the only wire(s) I need are the starter wire (purple). Is there anything I need to keep?

Bottom part, I’ll be keeping the headlights, turn signals. The red wire that goes to the external voltage regulator and AC unit can be deleted? What about the fusible ground line tied into the hot?

For the alternator, I was told to just run a 10g from battery to alternator. Does that sound correct? Also what’s the top circled wires for? Do I connect that to something?

[robertsjm711]

Is it currently running or still in the build stage?

If it was me I would trace all your questionable wires and see where they go, and eliminate the unnecessary. Making a list of needed wires may help, every ride has its own needs. I have a 5.3 that I rewired myself, and just used a 10g wire from the alternator to 12v. I used the stock fusible link from the stock harness.

I am not sure what "fusible ground line tied into the hot" could be, maybe someone using a wire for it unintended use?

[Ghost's68]

Originally Posted by robertsjm711

Is it currently running or still in the build stage?

If it was me I would trace all your questionable wires and see where they go, and eliminate the unnecessary. Making a list of needed wires may help, every ride has its own needs. I have a 5.3 that I rewired myself, and just used a 10g wire from the alternator to 12v. I used the stock fusible link from the stock harness.

I am not sure what "fusible ground line tied into the hot" could be, maybe someone using a wire for it unintended use?

The engine is just dropped in and I got the engine harness all wires up. I’m just trying to clean up the body wiring. So after looking at the diagram I see the circled wiring is for the HEI. I don’t have a coil to run it to so i think I’m ok for removing it.

As far as the fuse line I mentioned, I circled it. I’m guessing I will be good removing the old one and running a new 10g wire to the batter and this should be my ign source? That sound right?

[robertsjm711]

I would keep at least the fusible link, if you would get a short without it you will have a bad day...

[Ghost's68]

Originally Posted by robertsjm711

I would keep at least the fusible link, if you would get a short without it you will have a bad day...

So the circled fuse that ties into the hot wire, I keep that and and I connect the red wire to the battery?

[robertsjm711]

Yes because you don’t have a voltage regulator and the 12v to the alternator is supplied within the stand alone harness.

[Ghost's68]

Originally Posted by robertsjm711

Yes because you don’t have a voltage regulator and the 12v to the alternator is supplied within the stand alone harness.

Copy that!

Is 10g sufficient for the connection from th alternator to the battery?

Here’s what my plug looks like now? PO did some funky stuff with his 5.3 swap and I want to make sure things are correct.

[robertsjm711]

From the diagram the “where’s this go” wire seems to be 12v

I’d have to look at my setup but 10g seems right. If I remember about the diameter of a pencil.

I’d look at where those wires come from, and go from there.

[Ghost's68]

So the black 12v line in question doesn’t seem to go anywhere after it goes into the bulk head.

Also the ign pink wire that goes to my switch doesn’t seem it’s getting 12v since the orange/purple wire that goes to the starter has been deleted.

I’m I missing something?

I’m not a electrical guy at all, hence all the questions.

[dayj1]

Originally Posted by Ghost's68

So the black 12v line in question doesn’t seem to go anywhere after it goes into the bulk head.

Also the ign pink wire that goes to my switch doesn’t seem it’s getting 12v since the orange/purple wire that goes to the starter has been deleted.

I’m I missing something?

I’m not a electrical guy at all, hence all the questions.

The black 12v wire that goes directly to the battery (with the inline fuse) is for the ammeter.

The white/orange/purple wire would have been for the ignition system (it originally went to the coil).

The 12 gauge pink wire that you asked about is switched power from the ignition switch. The ignition switch is fed by the 12 gauge red wire from the switch to the bulkhead connector to the fuseable link to the battery.

[Ghost's68]

Originally Posted by dayj1

The black 12v wire that goes directly to the battery (with the inline fuse) is for the ammeter.

The white/orange/purple wire would have been for the ignition system (it originally went to the coil).

The 12 gauge pink wire that you asked about is switched power from the ignition switch. The ignition switch is fed by the 12 gauge red wire from the switch to the bulkhead connector to the fuseable link to the battery.

Since my gauges really never worked it sounds like I can delete the black wire for the ammeter?

Got cha. The pink wire is ign and is fed from the red power wire. The pink power doesn’t get its power directly from the battery but I’m guessing it gets distributed from the relay box? Is that correct?

Thanks for all the help guys!

[dayj1]

Originally Posted by Ghost's68

Since my gauges really never worked it sounds like I can delete the black wire for the ammeter?

If you don't want it for the ammeter, it's fine to remove it.

Originally Posted by Ghost's68

Got cha. The pink wire is ign and is fed from the red power wire. The pink power doesn’t get its power directly from the battery but I’m guessing it gets distributed from the relay box? Is that correct?

Yep.

[Ghost's68]

Originally Posted by dayj1

If you don't want it for the ammeter, it's fine to remove it.



Yep.

Now I’m starting to understand this mess much clearer now. For the red power wire to the battery with the “T’ed” in fuse ground?, should I keep that or can I do away with that safely? What’s its purpose? Also, it had a 4amp fuse, is that correct?

[robertsjm711]

That schematic doesn’t seem to match up to your earlier one, at least as far as colors. It’s hard to see everything through this forum, I’d hate to tell you the wrong thing.
I look at wiring in 3 categories. Power supply, ground and something with a purpose. The first two can be tied together wherever, it’s all the same circuit. The 3rd is like after a switch to a light - only one wire and no branches. Sometimes it helps to think it as a pipe system flowing water.
A multimeter with a buzzer and test light makes this way easier, just have to trace every one in question and decide if it’s needed, and if so is it correct. You might have to add some wires.

[dec010974]

is that pink wire, 12 gauge, a +12v switch power?

[Ghost's68]

Originally Posted by dec010974

is that pink wire, 12 gauge, a +12v switch power?

I’m not sure where it gets power from? Lol Im not only trying to fix things but also understand wiring in general.

[LH Lead-Foot]

As I look at the first wiring diagram, it shows an HEI distributor. OK, but this is a newer year schematic or supplied by Modern Vintage, but your issue on the 68, which OEM, has an ammeter. It uses an in-line glass tube fuse with BLK comes from the battery, to the negative side. The BLK/WHT comes from the amp meter to the alternator / regulator B+. Are you using an ammeter? I would use a volt meter instead, it's more useful.
The PPL wire is crank from the ignition switch. Your OEM harness, top connector was ORG/PPL is resistor wire to the started solenoid. During cranking, the solenoid "RUN" terminal supplies full battery to the external coil using points in the distributor. The coil is wired & design to operate correctly at 9-10volts. After cranking, the solenoid then switches back to the resistor wire, that drops voltage to the coil, for running. I would eliminated both fuse wires and re-purposed them in the connector.

The RED runs from the battery, thru a fusible link or a preferred MAXI fuse block, matching the systems amperage requirements, back to the ignition switch B+. PNK is always "Key Switched" color on GM's. ORN is fused hot at all times.

PPL now comes from the ignition switch, 10A fuse, into PCM for start request. The key switch supplies B+ in run & start into 10A fuse, thru the Park/Neutral Switch, (plus a Hidden No-Crank Sw. if you want), to starter relays coil. The starter relay is rated at 40A and fused at 40A, it goes to the starter solenoid.
The PCM supplies ground to the coil of the start relay. After receiving crank request, to allow cranking, the signal has to pass the PCM's truth table. What's that? If the PCM see's an PRM signal above 500 RPM, Too hot, etc. it will NOT allow cranking.
Hope that helps.

[Ghost's68]

Ok so I think I have one more question.

The PO wired the bottom purple wire to the SOL tab on the ignition switch, is that correct? Also, where does the top purple wire go? It’s just hanging there. Also, on the wiring digram there’s two wires going to the starter a solid 12g purple and a 20g W/org/purple, which is the one I connect to my starter connector?

Also the 12g solid purple wire is not connected anywhere after the bulk head do I connect this to any of the spots on the switch?

[dayj1]

Originally Posted by Ghost's68

The PO wired the bottom purple wire to the SOL tab on the ignition switch, is that correct?

Yes

Originally Posted by Ghost's68

Also, where does the top purple wire go?

The starter solenoid via the bulkhead connector.

Originally Posted by Ghost's68

Also, on the wiring digram there’s two wires going to the starter a solid 12g purple and a 20g W/org/purple, which is the one I connect to my starter connector?

The white/orange/purple wire is a resistance wire that would have been for the ignition system (it originally went to the coil via the starter solenoid).

Originally Posted by Ghost's68

Also the 12g solid purple wire is not connected anywhere after the bulk head do I connect this to any of the spots on the switch?

If it's not clear from above, the starter circuit (12 gauge purple wire) starts at the ignition switch, goes to the NSS switch on the column, goes to the bulkhead connector, and ends at the starter solenoid.

[Ghost's68]

This is how my switch is wired up currently

[LH Lead-Foot]

What dayj1 said!
PLL is the start circuit from the ignition switch to the starter. Your vehicle appears to have a Neutral Safety Switch on the column, which you can keep or by-pass. If you have a column shift, it is for safety, but if you went to a floor shift, either automatic or manual, you should have something wired to interrupt the start circuit.
As stated, the OEM schematic shows PPL to the bulk-head connector, where it turns into WHT/ORN/PPL to the starter solenoid switch and is a resistive wire...Delete it, then re-purpose it's cavity at the bulk-head for something else.
You have provided nice photos and you have posted a period schematic, so you have basically everything you need.
Just note that the starter solenoid circuit is close to 38 amps peak current cold, then drops to 22 amps continuous during cranking. If you want a secrete "Theft-No-Start" toggle switch under the dash, purchase on capable of that high of current. I would choose to use a simple 4 terminal relay to handle a 40 amp circuit and please make sure there are fuses protecting the circuits. Hope that helps. I don't have the posting skills you or dayj1 have learned on this forum, but his explanation is all you need to get cranking.

[Ghost's68]

Originally Posted by dayj1

Yes



The starter solenoid via the bulkhead connector.



The white/orange/purple wire is a resistance wire that would have been for the ignition system (it originally went to the coil via the starter solenoid).



If it's not clear from above, the starter circuit (12 gauge purple wire) starts at the ignition switch, goes to the NSS switch on the column, goes to the bulkhead connector, and ends at the starter solenoid.

Originally Posted by LH Lead-Foot

What dayj1 said!
PLL is the start circuit from the ignition switch to the starter. Your vehicle appears to have a Neutral Safety Switch on the column, which you can keep or by-pass. If you have a column shift, it is for safety, but if you went to a floor shift, either automatic or manual, you should have something wired to interrupt the start circuit.
As stated, the OEM schematic shows PPL to the bulk-head connector, where it turns into WHT/ORN/PPL to the starter solenoid switch and is a resistive wire...Delete it, then re-purpose it's cavity at the bulk-head for something else.
You have provided nice photos and you have posted a period schematic, so you have basically everything you need.
Just note that the starter solenoid circuit is close to 38 amps peak current cold, then drops to 22 amps continuous during cranking. If you want a secrete "Theft-No-Start" toggle switch under the dash, purchase on capable of that high of current. I would choose to use a simple 4 terminal relay to handle a 40 amp circuit and please make sure there are fuses protecting the circuits. Hope that helps. I don't have the posting skills you or dayj1 have learned on this forum, but his explanation is all you need to get cranking.

Again, I thank you very much for the help. I’m pretty sure I have my truck wired to be able to crank it safely now. You guys are the best!!

I hope this thread is helpful for someone in the future going through the same thing I was.

[halfstep]

Hey Ghost -
I can't help you with your questions, but it looks like you got where you needed to go, so I've got a couple questions for you -
I'm considering the Modern Vintage harness for my conversion. They sounded very accommodating on the phone but there's little info on the site and it hasn't been updated in ages. I'd like to hear your opinions on the product/process, etc. and maybe some photos of the harness? Thanks and good luck.

[Ghost's68]

Originally Posted by halfstep

Hey Ghost -
I can't help you with your questions, but it looks like you got where you needed to go, so I've got a couple questions for you -
I'm considering the Modern Vintage harness for my conversion. They sounded very accommodating on the phone but there's little info on the site and it hasn't been updated in ages. I'd like to hear your opinions on the product/process, etc. and maybe some photos of the harness? Thanks and good luck.

HS, the harness is very nice! The busman fuse box is really nice and has room for expansion. Turn around was actually quicker then expected. As far as I know every harness is tested on their test engines/trans for proper function. I have been asking them a bunch of questions on Instagram and they have always responded within an hour. The wires were all well labeled. Here’s some quick pics

[69BUCKET]

Ghost, where did you mount ECU and where did you pass it through firewall?