LS swap wiring questions
Thread Starter
Drifting
Joined: Jul 2020
Posts: 1,501
Likes: 323
From: San Diego
LS swap wiring questions
I’m doing an LS swap on my 68. I’m putting in a GEN III LS6 it came without the engine harness. I’m not sure if the best way to go is to buy a truck harness and have it modified, a Corvette harness and have it modified, or by the Holley terminator system. I did have a Holly sniper on the car before with my previous engine, and I hated the Hollys sniper.
I don’t understand how the new engine harness wires into the old engine harness. I assume at some point they have to connect somewhere in order to communicate with other parts of the car and things like that but somebody told me they are standalone.
The engine came with the engine computer, and I have a guy that could modify the computer and modify an engine harness that I sent him to work with the car.
A truck harness is about $650, a corvette harness is about $800 and the Holley Terminator is $1500. I will still need a TAC module with either harness but I dont think I do with the Holley Terminator.
which is the best route to go?
I don’t understand how the new engine harness wires into the old engine harness. I assume at some point they have to connect somewhere in order to communicate with other parts of the car and things like that but somebody told me they are standalone.
The engine came with the engine computer, and I have a guy that could modify the computer and modify an engine harness that I sent him to work with the car.
A truck harness is about $650, a corvette harness is about $800 and the Holley Terminator is $1500. I will still need a TAC module with either harness but I dont think I do with the Holley Terminator.
which is the best route to go?
Pro
Joined: Dec 2015
Posts: 578
Likes: 107
From: colo
I installed a Gen V LT1 in my 78. I got my wiring harness from PSI wiring ( about $1500 ) . I think you could get by with the truck harness and figure out which wire / connector goes where and plug them in. It could help if you can mark each connector as you remove it from the old engine (?) There will be some additional wiring- like fuel pump and power that you have to add, but the internet search helps a lot. I too would probaly stay away from the Holley since your past experience , and they are very proud of their product because the price is so high.
Good luck making a decision.
Good luck making a decision.
Melting Slicks
Joined: Sep 2010
Posts: 3,305
Likes: 697
So my .02.
What trans? Stick or auto? The 24 tooth crank reluctor LS engines need only one ECM for manual or auto.
The LS engine harness is basically stand alone engine wise. Your current chassis harness only needs to supply a full 12 volt on start and run. Make sure on run the LS gets a full 12 volts.
I would run a DBC throttle body from 2002 Camaro since you have a LS6 intake. No messing around with a TAC truck module and DBW pedal.
ECM wise and LS harness wise I would go with a known supplier on here or LS1tech.com. I like Speartech and Howell. I buy the ECM and engine harness from one supplier. They can load a base tune in the ECM to get you running. Also if you have issues one supplier to talk to.
Holley? Good stuff but using all GM parts replacement parts are only a NAPA store away.
What trans? Stick or auto? The 24 tooth crank reluctor LS engines need only one ECM for manual or auto.
The LS engine harness is basically stand alone engine wise. Your current chassis harness only needs to supply a full 12 volt on start and run. Make sure on run the LS gets a full 12 volts.
I would run a DBC throttle body from 2002 Camaro since you have a LS6 intake. No messing around with a TAC truck module and DBW pedal.
ECM wise and LS harness wise I would go with a known supplier on here or LS1tech.com. I like Speartech and Howell. I buy the ECM and engine harness from one supplier. They can load a base tune in the ECM to get you running. Also if you have issues one supplier to talk to.
Holley? Good stuff but using all GM parts replacement parts are only a NAPA store away.
Race Director
Joined: Mar 2017
Posts: 11,944
Likes: 4,504
From: Virginia
I'm using the Holley Terminator X for my LS6. That's with a TKX (so no trans control needed). I expect it to have all of the wiring I need. I have all of the LS6 stuff, too, which I'll just sell on eBay.
By "TAC", are you using the stock intake with the fly-by-wire throttle, instead of converting to a cable-actuated throttle body? Are you using a C5 throttle pedal as well?
By "TAC", are you using the stock intake with the fly-by-wire throttle, instead of converting to a cable-actuated throttle body? Are you using a C5 throttle pedal as well?
Thread Starter
Drifting
Joined: Jul 2020
Posts: 1,501
Likes: 323
From: San Diego
So I am running a TKO500 5 speed trans. I am not sure about the throttle. I was told I needed a TAC module by a guy I sent my PCM to. He open it up and removed some coding for knock sensors and stuff and I think some emissions. He said he can modify a wire harness for me for $450 if I send him the harness.
The computer mods were $50 and since I had the computer I figured I would go that route but then a wiring harness is about $200-300 plus his $450 and shipping Im almost $1000 in to the wiring for used stuff.
The computer mods were $50 and since I had the computer I figured I would go that route but then a wiring harness is about $200-300 plus his $450 and shipping Im almost $1000 in to the wiring for used stuff.
Race Director
Joined: Mar 2017
Posts: 11,944
Likes: 4,504
From: Virginia
So I am running a TKO500 5 speed trans. I am not sure about the throttle. I was told I needed a TAC module by a guy I sent my PCM to. He open it up and removed some coding for knock sensors and stuff and I think some emissions. He said he can modify a wire harness for me for $450 if I send him the harness.
The computer mods were $50 and since I had the computer I figured I would go that route but then a wiring harness is about $200-300 plus his $450 and shipping Im almost $1000 in to the wiring for used stuff.
The computer mods were $50 and since I had the computer I figured I would go that route but then a wiring harness is about $200-300 plus his $450 and shipping Im almost $1000 in to the wiring for used stuff.
On the cheap, there are some tips in my budget LM7 build thread (page 3). You can program the ECU yourself, and you can absolutely delete the TAC.
Both systems will use a cable-driven throttle body.
https://www.corvetteforum.com/forums...to-a-c3-3.html
Pro
Joined: Oct 2017
Posts: 568
Likes: 205
I did the Holley terminator X in my Camaro. Fast forward a few years and the Terminator with DBW, and Trans control is over $2k. I went with Aces EFI Jackpot LS system this time for my C3 project. It has more features than the Terminator for $750 less.
https://acesefi.com/products/the-jackpot-ecu
https://acesefi.com/products/the-jackpot-ecu
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Thread Starter
Drifting
Joined: Jul 2020
Posts: 1,501
Likes: 323
From: San Diego
I did the Holley terminator X in my Camaro. Fast forward a few years and the Terminator with DBW, and Trans control is over $2k. I went with Aces EFI Jackpot LS system this time for my C3 project. It has more features than the Terminator for $750 less.
https://acesefi.com/products/the-jackpot-ecu
https://acesefi.com/products/the-jackpot-ecu
Pro
Joined: Oct 2017
Posts: 568
Likes: 205
I have both the Holley and the Aces. I don’t have the Aces installed yet so I can only compare visually. A few first impressions of the Aces.
The Aces ECU is much smaller than the Terminator. Should be easier to find a place to mount being smaller in size. It also a solid metal case versus Holley. Wiring harness on Aces looks similar, maybe a touch nicer than Holley being the main harness is longer. Ace kit came with 2 Oxygen sensors, my Terminator came with 1. Aces has a 7” screen, Holley is a ridiculous small 3.5” screen. Aces came with harnesses for 24x and 58x included. Aces uses OE map sensor included, my Holley has the map sensor built into the ECU. Not sure if one is better than the other. Overall I’m pretty impressed with the Aces given it’s 40% less than the Holley.
The Aces ECU is much smaller than the Terminator. Should be easier to find a place to mount being smaller in size. It also a solid metal case versus Holley. Wiring harness on Aces looks similar, maybe a touch nicer than Holley being the main harness is longer. Ace kit came with 2 Oxygen sensors, my Terminator came with 1. Aces has a 7” screen, Holley is a ridiculous small 3.5” screen. Aces came with harnesses for 24x and 58x included. Aces uses OE map sensor included, my Holley has the map sensor built into the ECU. Not sure if one is better than the other. Overall I’m pretty impressed with the Aces given it’s 40% less than the Holley.
Last edited by TorchZ51; Jul 27, 2024 at 01:07 AM.
Burning Brakes
Joined: Aug 2016
Posts: 1,000
Likes: 283
From: New York
You do NOT need a TAC module if you are going aftermarket ECU, the Holley is not compatible with that TB, you will need a custom harness to use that TB I can find who makes it. ONLY the Terminator X or dominator can do DBW.
If you don't know how to tune and don't have HP tuners stay away from factory, unless you want to do a mail order preconfigured ecu and be done with it.
The Terminator series can run an external map, you don't need to run the internal. I run 3 dominators, an HP, and a Term. They always work, easy to tune, have tons of support. Your ECU is what will get you home or leave you stranded....a little cheaper and a 7" screen vs 3.5 isn't a big difference for me personally. The dual O2 IS a much better tho.
If you don't know how to tune and don't have HP tuners stay away from factory, unless you want to do a mail order preconfigured ecu and be done with it.
The Terminator series can run an external map, you don't need to run the internal. I run 3 dominators, an HP, and a Term. They always work, easy to tune, have tons of support. Your ECU is what will get you home or leave you stranded....a little cheaper and a 7" screen vs 3.5 isn't a big difference for me personally. The dual O2 IS a much better tho.
Burning Brakes
Joined: Sep 2020
Posts: 863
Likes: 186
From: CT
I’ve done a few LS swaps. On my 78 I did the termX and it’s my go to as the termX is great and user friendly. I did a stock cable TB and that’s all you need. You will need some additional wiring which I always do.
fan control, you will need to convert to electric fans which is always a good idea. Figure out how you want to wire those and have the Holley control it. (Uses ground outputs to control or activate relays.
power and ground hookups I always go off the battery or a remote battery direct connection.
get a LS1 3 wire coolant temp sensor and factory gauge can be used.
I always add a 100amp+ circuit breaker to the charge side of the alternator that goes to the battery.
I always add a disconnect and fuse/circuit breaker to the main lug on the battery (usually ground side)
get a universal LS throttle cable and you can adapt it to the stock pedal and it will fit the LS TB.
Holley tach signal will work with stock gauge but you will need to figure out the speedo. Use stock oil pressure gauge sender and voltage etc will work.
fan control, you will need to convert to electric fans which is always a good idea. Figure out how you want to wire those and have the Holley control it. (Uses ground outputs to control or activate relays.
power and ground hookups I always go off the battery or a remote battery direct connection.
get a LS1 3 wire coolant temp sensor and factory gauge can be used.
I always add a 100amp+ circuit breaker to the charge side of the alternator that goes to the battery.
I always add a disconnect and fuse/circuit breaker to the main lug on the battery (usually ground side)
get a universal LS throttle cable and you can adapt it to the stock pedal and it will fit the LS TB.
Holley tach signal will work with stock gauge but you will need to figure out the speedo. Use stock oil pressure gauge sender and voltage etc will work.
Pro
Joined: Oct 2017
Posts: 568
Likes: 205
Looks like you will need this kit if going with DBW and manual trans. AS2011-3
https://acesefi.com/products/the-jac...42097639063758
Note it supports the GM throttle body 8pin and newer 6 pin. You’ll need to buy the GM DBW pedal 10379038
Pro
Joined: Oct 2017
Posts: 568
Likes: 205
You do NOT need a TAC module if you are going aftermarket ECU, the Holley is not compatible with that TB, you will need a custom harness to use that TB I can find who makes it. ONLY the Terminator X or dominator can do DBW.
If you don't know how to tune and don't have HP tuners stay away from factory, unless you want to do a mail order preconfigured ecu and be done with it.
The Terminator series can run an external map, you don't need to run the internal. I run 3 dominators, an HP, and a Term. They always work, easy to tune, have tons of support. Your ECU is what will get you home or leave you stranded....a little cheaper and a 7" screen vs 3.5 isn't a big difference for me personally. The dual O2 IS a much better tho.
If you don't know how to tune and don't have HP tuners stay away from factory, unless you want to do a mail order preconfigured ecu and be done with it.
The Terminator series can run an external map, you don't need to run the internal. I run 3 dominators, an HP, and a Term. They always work, easy to tune, have tons of support. Your ECU is what will get you home or leave you stranded....a little cheaper and a 7" screen vs 3.5 isn't a big difference for me personally. The dual O2 IS a much better tho.
My Terminator works great, but the Aces is LOT less expensive so going to give it a shot. Holley getting a bit too proud of thier stuff. Other options on the market now.
Last edited by TorchZ51; Jul 27, 2024 at 02:15 PM.
Thread Starter
Drifting
Joined: Jul 2020
Posts: 1,501
Likes: 323
From: San Diego
Yes, but tbh I had the Holley Sniper on my last set up and it was the biggest piece of expensive garbage. Holley would not stand behind the terrible product they sold and eventually redesigned it to the Sniper 2. I assume this may have fixed most issues but there are alot of people who paid good money for the original Sniper and its bad. I have a hard time reaching into my pocket to give Holley anymore money for any of their systems. If there is an alternative then I like that option.
Melting Slicks
Joined: Sep 2010
Posts: 3,305
Likes: 697
Again my .02.
What if the aftermarket suppliers go bust? No more parts if needed. No more tech support if needed.
Your build seems fairly mild. No question I would use stock GM components thru out. A bit more cost wise from a supplier on this forum for the ECM and wiring harness but any good tuner can tune it and you won't have to touch it again.
What if the aftermarket suppliers go bust? No more parts if needed. No more tech support if needed.
Your build seems fairly mild. No question I would use stock GM components thru out. A bit more cost wise from a supplier on this forum for the ECM and wiring harness but any good tuner can tune it and you won't have to touch it again.
Burning Brakes
Joined: Sep 2020
Posts: 863
Likes: 186
From: CT
I looked at the Aces EFI yesterday and wanted to get more info. It's hard to say its worth the money besides it telling you that it works with dual "bosch" WB02s and 24x and 58x reluctors. I doesn't say anything about inputs/outputs and does it do PWM? What are the limits of the ECM? FWIW there is a system out there that basically does these same things and its about as cheap Fitech ultimate LS which I have their system from 4-5years ago. It worked but it wasn't great. I went to the TermX and haven't looked back, that thing just works and its easy to use. I also didn't pay more than $1k for each system a few years ago but man they have gone up in price.
Fitech and Aces ECMs look very similar, both do 24x and 58x, both due dual Bosch WB02s and both come with that POS Bosch fake LS9 map sensor. I haven't looked further to see if I can find a manual for one to get more specifics on the Aces limitations but I'm def getting flashbacks to the Fitech system (first budget EFI swap system with self tuning).
Fitech and Aces ECMs look very similar, both do 24x and 58x, both due dual Bosch WB02s and both come with that POS Bosch fake LS9 map sensor. I haven't looked further to see if I can find a manual for one to get more specifics on the Aces limitations but I'm def getting flashbacks to the Fitech system (first budget EFI swap system with self tuning).