Seeking Basic Charging System Wiring Guidance

I'm currently working on an LS swap and battery relocation to the trunk but I have pretty limited wiring knowledge. This is the rough diagram for my wiring plan. I'm planning to mount that distribution block on the firewall and have all my 12V power branch out from there. So far I've relocated and wired the battery, battery ground, circuit breaker and ran the 1 gauge cable from the battery/circuit breaker up through the firewall.

Is this proper and does it make sense? Does anyone have any comments on the 250A breaker size?

FYI I didn't bother adding the other grounds to the diagram but I will have engine block to chassis, engine harness to block and chassis, etc.

P.S. I don't know why Servimg automatically rotates my photos clockwise 90 degrees and I cannot figure out how to stop that from happening... quite frustrating.

[You must be registered and logged in to see this image.]

Unfortunately, i can't help much with wiring, however, i do know that you will need this for your LS alternator to run at full power:
[You must be registered and logged in to see this link.]

We smoked 3 or 4 alternators until we figured out adding a resistance like the wire above. We were in the middle of One Lap of America and didnt have access to the special cable so we wire an instrument panel light in series to the exciter wire and havent replaced an alternator since. my $.02.

Overall your wiring sizes and plan are sound. With one exception, the 250 amp breaker will give you fits. An LS starter generally draws 250-300 amps by itself. The other accessories will overload your breaker causing it to trip. I generally don't run a breaker on the main feed. Just a remote battery disconnect.

MotoRider42HC wrote:Unfortunately, i can't help much with wiring, however, i do know that you will need this for your LS alternator to run at full power:
[You must be registered and logged in to see this link.]

I have a standalone LS wiring harness that I'm going to be installing that already has the proper alternator plug. Do I still need this? I'm not sure what this actually does differently?

expuppy23 wrote:We smoked 3 or 4 alternators until we figured out adding a resistance like the wire above.  We were in the middle of One Lap of America and didnt have access to the special cable so we wire an instrument panel light in series to the exciter wire and havent replaced an alternator since.  my $.02.

I'm using the stock GM computer along with a standalone wiring harness that has the correct connector already. I don't think I would need a resistor wire if I'm not mistaken?

ndog52 wrote:I'm using the stock GM computer along with a standalone wiring harness

Are you using an OEM engine wiring harness, or an actual aftermarket wiring harness?

For example, the Holly Terminator X wiring harness was missing the injector harness and alternator harness, and etc misc items, that I all had to buy separately and/or wire myself.

If you are using an OEM harness matched to your OEM ECU, then you should be mostly OK.

MotoRider42HC wrote:

ndog52 wrote:I'm using the stock GM computer along with a standalone wiring harness

Are you using an OEM engine wiring harness, or an actual aftermarket wiring harness?

For example, the Holly Terminator X wiring harness was missing the injector harness and alternator harness, and etc misc items, that I all had to buy separately and/or wire myself.

If you are using an OEM harness matched to your OEM ECU, then you should be mostly OK.

I'm using an aftermarket, premade harness specifically for my engine. Here's a link:

[You must be registered and logged in to see this link.]

Insulator wrote:Overall your wiring sizes and plan are sound. With one exception, the 250 amp breaker will give you fits. An LS starter generally draws 250-300 amps by itself. The other accessories will overload your breaker causing it to trip. I generally don't run a breaker on the main feed. Just a remote battery disconnect.

Second this. My car has no main breaker, either.

ndog52 wrote:[You must be registered and logged in to see this link.]

Holy mother of god, $600? I guess you're paying for "trouble free" which I wish I had, lol.

MotoRider42HC wrote:

ndog52 wrote:[You must be registered and logged in to see this link.]

Holy mother of god, $600?  I guess you're paying for "trouble free" which I wish I had, lol.

I'm not sure where you're from, but that's $600 Canadian dollars which is more like $440 USD. Still a bit pricey but it definitely should make it a breeze. At least that's the goal lol...

MotoRider42HC wrote:Unfortunately, i can't help much with wiring, however, i do know that you will need this for your LS alternator to run at full power:
[You must be registered and logged in to see this link.]

either that or splice in a 470ohm resistor in line with red pin 15 on ecu. (obviously this can vary from different year and displacement of block but that's what matched on my 97 LS1 vette; double check with lt1swap.com for proper wiring pinout that matches yours)

but for only 20 some bucks getting that pigtail connector seems much easier.
also as another side comment, Bob from hotrodz showed me the error in my ways of spending countless hours on fixing, cleaning up the inherited harness with my factory ECU that could have been saved by buying a decent cheap amazon 4L60 gen 3 harness. link he gave me doesn't exist on amazon anymore but there's lots of copycats and only like $250USD.

Gutterboy wrote:

MotoRider42HC wrote:Unfortunately, i can't help much with wiring, however, i do know that you will need this for your LS alternator to run at full power:
[You must be registered and logged in to see this link.]

either that or splice in a 470ohm resistor in line with red pin 15 on ecu. (obviously this can vary from different year and displacement of block but that's what matched on my 97 LS1 vette; double check with lt1swap.com for proper wiring pinout that matches yours)

but for only 20 some bucks getting that pigtail connector seems much easier.
also as another side comment, Bob from hotrodz showed me the error in my ways of spending countless hours on fixing, cleaning up the inherited harness with my factory ECU that could have been saved by buying a decent cheap amazon 4L60 gen 3 harness. link he gave me doesn't exist on amazon anymore but there's lots of copycats and only like $250USD.

Hi Gutterboy, I've been following your build quite closely and it's been an absolute wealth of knowledge so thank you very much for that.

I've already bought one of the premade standalone harnesses. I'm just trying to figure out if I need to install that resistor pigtail or if my harness would already have that functionality built in. I don't see why it wouldn't, given that I am using a stock PCM and that the harness is designed specifically for my LM7 which is running the stock alternator.

as per title i think this is where the issue begins. now unfortunately i was knee deep in this about a year ago and didn't completely document this properly in my thread but here goes my best attempt.

the dummy or CEL lamp circuit in the original chevy wiring schematic is what causes the pull down of the voltage so you don't burn the diodes in the alternator for the charging.

so you either need to run it through the ! light of the porsche system for same pull down of which i have no idea what resistance that poses and whether its enough or you just simply add that pigtail or in my case i didn't know about that so as per many other threads in a random google; you'll find many peopel talking about adding a 470 ohm 1/2 watt resistor in series with that red ecm block pin 15 to pull that voltage down properly. When i opened up my wiring harness from when it was previously swapped into an rx7, i found this same wire on that pin with a resistor that was not 470 ohm but some other value soldered in series. Since the solder job was atrocious i cut it and with some spare ECU pin's i put a new red tail wire in the ecu and soldered my new 470 ohm resistor and this the became my new alternator wire for the LS1 factory harness plug.

so because you are still doing a swap, i wouldn't hesitate on getting said pigtail adapter as your native harness does not have the porsche light cct "built in". you need that pull down or your alternator will be done at some point.