How to prep a 3rd gen harness
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Re: How to prep a 3rd gen harness
So I got to the finishing points of the harness but it seems like I have more connectors still attached to the c100. On the connectors them selves there is on 1 wire going to the c100 and all the other ones are cut off. What do I do to them?
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From: NJ
Car: 92 Firebird
Engine: 4.8 LR4
Transmission: T56
Axle/Gears: 3.45 9 Bolt
Re: How to prep a 3rd gen harness
Not really useful, need a shot of the wires in the cavities, and/or the connectors on the ends of the wires. Also need the year of your car. Try looking at the pin outs at the Austin thirdgen site
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Re: How to prep a 3rd gen harness
Thank you, thank you, thank you, Pocket!
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Re: How to prep a 3rd gen harness
anyone know if I am not keeping the stock gauges in the dash then what is left coming out of the firewall besides the headlights? im putting in a holley terminator kit with an ls3 its a 1988 iroc had the 5.7 tpi
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Car: 91 Trans Am
Re: How to prep a 3rd gen harness
Stock gauges can be retained with a terminator kit. I make a harness specifically for this purpose
There are only four gauges in question for any swap with any setup: Speedo, tach, oil press and coolant temp
Speedo and tach are compatible with any modern EFI system. Speedo takes a standard 4,000ppm signal and tach is universal 6/8cyl
Oil is simple, just use the stock or LS sender. Holley has a three wire sensor behind the intake, but theres a second port above the oil filter that can be drill/tapped for 1/8NPT like factory. SBCs or engines without room for two senders can use a tee adapter to put both on one port behind the intake
Coolant gauge is also simple. For LS engines, the 98 fbody 3 wire CTS screws right in the cyl head. Top two wires to the CTS for the ECM, bottom is gauge sender. Alternatively, you can drill the pass cyl head port to 3/8NPT and reuse the stock sender. If can also be turned down on a lathe to 12 x 1.5mm so no drilling is needed
SBC guys can use a three wire CTS from a mid 90's FWD 3.8 V6. Same thing as LS, but 3/8NPT
Voltage gauge and fuel level are unaffected by any conversion
There are only four gauges in question for any swap with any setup: Speedo, tach, oil press and coolant temp
Speedo and tach are compatible with any modern EFI system. Speedo takes a standard 4,000ppm signal and tach is universal 6/8cyl
Oil is simple, just use the stock or LS sender. Holley has a three wire sensor behind the intake, but theres a second port above the oil filter that can be drill/tapped for 1/8NPT like factory. SBCs or engines without room for two senders can use a tee adapter to put both on one port behind the intake
Coolant gauge is also simple. For LS engines, the 98 fbody 3 wire CTS screws right in the cyl head. Top two wires to the CTS for the ECM, bottom is gauge sender. Alternatively, you can drill the pass cyl head port to 3/8NPT and reuse the stock sender. If can also be turned down on a lathe to 12 x 1.5mm so no drilling is needed
SBC guys can use a three wire CTS from a mid 90's FWD 3.8 V6. Same thing as LS, but 3/8NPT
Voltage gauge and fuel level are unaffected by any conversion
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Re: How to prep a 3rd gen harness
I am installing the terminator kit and the holley efi gauges there will be no stock gauges in the car what i need some info on is if i remove the harness from the passenger side with the ecm and the 2 on the driver side, one I believe is the headlights what happens to the rest of the car interior lights rail lights and such
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Car: 91 Trans Am
Re: How to prep a 3rd gen harness
For 88-89 C207 has a few required wires, mostly for gauges
B INJ 1 fuse
C MIL
D Fan rly 12v (pin 86)
F PCM fuse
G INJ 2 fuse
K Speedo (firebird only)
M Gauges grd
N P/neutral
Since you're not running the stock cluster, Id use one of the fuse points for your Holley IGN relay and ground pin M. In your case, Id snip the C207 off the engine harness and reuse those two pins. I dont recommend modifying the dash harness in a permanent fashion
Yes, the C100 splits onto two halves. The large side is for the engine and the small front lights
You'll need to keep all the big wires from the C100 plus wiper wiring. Power, fuel pump, starter. The small stuff are tach, oil press, coolant and emissions fuse point. None are kept in your particular instance
B INJ 1 fuse
C MIL
D Fan rly 12v (pin 86)
F PCM fuse
G INJ 2 fuse
K Speedo (firebird only)
M Gauges grd
N P/neutral
Since you're not running the stock cluster, Id use one of the fuse points for your Holley IGN relay and ground pin M. In your case, Id snip the C207 off the engine harness and reuse those two pins. I dont recommend modifying the dash harness in a permanent fashion
Yes, the C100 splits onto two halves. The large side is for the engine and the small front lights
You'll need to keep all the big wires from the C100 plus wiper wiring. Power, fuel pump, starter. The small stuff are tach, oil press, coolant and emissions fuse point. None are kept in your particular instance
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From: Florida
Car: 1989 Camaro RS
Engine: LH6
Transmission: T56
Axle/Gears: 3.42 Auburn Posi
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Car: 1991 Camaro RS
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Re: How to prep a 3rd gen harness
Stock gauges can be retained with a terminator kit. I make a harness specifically for this purpose
There are only four gauges in question for any swap with any setup: Speedo, tach, oil press and coolant temp
Speedo and tach are compatible with any modern EFI system. Speedo takes a standard 4,000ppm signal and tach is universal 6/8cyl
Oil is simple, just use the stock or LS sender. Holley has a three wire sensor behind the intake, but theres a second port above the oil filter that can be drill/tapped for 1/8NPT like factory. SBCs or engines without room for two senders can use a tee adapter to put both on one port behind the intake
Coolant gauge is also simple. For LS engines, the 98 fbody 3 wire CTS screws right in the cyl head. Top two wires to the CTS for the ECM, bottom is gauge sender. Alternatively, you can drill the pass cyl head port to 3/8NPT and reuse the stock sender. If can also be turned down on a lathe to 12 x 1.5mm so no drilling is needed
SBC guys can use a three wire CTS from a mid 90's FWD 3.8 V6. Same thing as LS, but 3/8NPT
Voltage gauge and fuel level are unaffected by any conversion
There are only four gauges in question for any swap with any setup: Speedo, tach, oil press and coolant temp
Speedo and tach are compatible with any modern EFI system. Speedo takes a standard 4,000ppm signal and tach is universal 6/8cyl
Oil is simple, just use the stock or LS sender. Holley has a three wire sensor behind the intake, but theres a second port above the oil filter that can be drill/tapped for 1/8NPT like factory. SBCs or engines without room for two senders can use a tee adapter to put both on one port behind the intake
Coolant gauge is also simple. For LS engines, the 98 fbody 3 wire CTS screws right in the cyl head. Top two wires to the CTS for the ECM, bottom is gauge sender. Alternatively, you can drill the pass cyl head port to 3/8NPT and reuse the stock sender. If can also be turned down on a lathe to 12 x 1.5mm so no drilling is needed
SBC guys can use a three wire CTS from a mid 90's FWD 3.8 V6. Same thing as LS, but 3/8NPT
Voltage gauge and fuel level are unaffected by any conversion
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Joined: Apr 2019
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Re: How to prep a 3rd gen harness
I am doing an ls swap but buying a stand alone harness and fuse box that will already have everything needed as far as for the engine including ignition switch signal speedo and tach hook ups I also have custom gauge cluster also what would need to be done to my 3rd gen harness just to run the basics accessories, cluster light, turn signals etc basically just everything for the body besides starter wire and main 12v to ign and 12v to fuse block also how would you go about getting power to this fuse block if you have the time thanks
92 camaro v6 harness btw
92 camaro v6 harness btw
Last edited by todd105; Apr 30, 2020 at 09:18 AM.
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From: Oregon
Car: 87 Camaro Multi-port Fl
Engine: Ls 5.3
Transmission: 4L 60 E
Re: How to prep a 3rd gen harness
This thread is a basic guide to stripping a 3rd gen harness and preparing it to be mated with a new PCM whether its a LT1, LS1, 0411 SBC, aftermarket or generic carb
Retaining part of the original harness allows you to keep the stock gauges without rewiring the interior harness. It also makes finding IGN power easy for the new harness
Ok before we begin, Ill get on my soapbox and try to save a bit of money. If you have a 90-92 TPI do not cut the first wire on the harness. Sell it
Buy a V6 or TBI harness and modify that one as they are significantly cheaper and the sale of the SD TPI harness should net you a good chunk back
Everything V6/TBI/TPI about your old harness is being removed
Next lets talk about harness selection. Match the trans type of the harness to the original trans equipped in the car. This will save you tons of headaches with reverse lights, pedal wiring and what-not. Dash harnesses are trans specific and are VERY rarely swapped.
Ok lets get started. This is most of a V6 harness pulled from a 91 camaro. Notice the coil, dist and AC wiring is hacked and in some places missing. Do not fret as none of this is retained
Attachment 426533
Label all of the connectors you know, namely the ones that are connected to your gauges
Next strip all of the loom/tape from the harness so you're left with a giant pile of spaghetti
Attachment 426534
Now start bunching up individual connectors and taping them back so they dont get tangled up so much
All of them dont have to be done, just the more you do the easier the harness will be to separate
Attachment 426535
Attachment 426536
Max pics reached
Retaining part of the original harness allows you to keep the stock gauges without rewiring the interior harness. It also makes finding IGN power easy for the new harness
Ok before we begin, Ill get on my soapbox and try to save a bit of money. If you have a 90-92 TPI do not cut the first wire on the harness. Sell it
Buy a V6 or TBI harness and modify that one as they are significantly cheaper and the sale of the SD TPI harness should net you a good chunk back
Everything V6/TBI/TPI about your old harness is being removed
Next lets talk about harness selection. Match the trans type of the harness to the original trans equipped in the car. This will save you tons of headaches with reverse lights, pedal wiring and what-not. Dash harnesses are trans specific and are VERY rarely swapped.
Ok lets get started. This is most of a V6 harness pulled from a 91 camaro. Notice the coil, dist and AC wiring is hacked and in some places missing. Do not fret as none of this is retained
Attachment 426533
Label all of the connectors you know, namely the ones that are connected to your gauges
Next strip all of the loom/tape from the harness so you're left with a giant pile of spaghetti
Attachment 426534
Now start bunching up individual connectors and taping them back so they dont get tangled up so much
All of them dont have to be done, just the more you do the easier the harness will be to separate
Attachment 426535
Attachment 426536
Max pics reached
Joined: Mar 2001
Posts: 10,404
Likes: 2,081
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: How to prep a 3rd gen harness
This thread is Part 1 of the wiring guide. Key posts are #1-3, 25. Read those. The rest is just Q&A conversation.
Part II is here, https://www.thirdgen.org/forums/ltx-...rt-finish.html
Key posts are #1-7, 17. The rest is Q&A conversation.
After that Pocket wrote up another example as he built a harness for a LS1/T56 swap into a '89 GTA. Key posts are #1, 2. https://www.thirdgen.org/forums/ltx-...revisited.html
He also created a thread with pinouts of C100 and C207 connectors for various years.
https://www.thirdgen.org/forums/ltx-...formation.html
Just a note to consider: You have choices where you want to tap power for the engine harness. Pocket was a fan of reusing as much of the stock fuse panel as possible so you'll see very few add-on's in his examples. Other people have added underhood power centers and made less use of the stock fuse panel. It's really up to you, just gotta choose your path.
Part II is here, https://www.thirdgen.org/forums/ltx-...rt-finish.html
Key posts are #1-7, 17. The rest is Q&A conversation.
After that Pocket wrote up another example as he built a harness for a LS1/T56 swap into a '89 GTA. Key posts are #1, 2. https://www.thirdgen.org/forums/ltx-...revisited.html
He also created a thread with pinouts of C100 and C207 connectors for various years.
https://www.thirdgen.org/forums/ltx-...formation.html
Just a note to consider: You have choices where you want to tap power for the engine harness. Pocket was a fan of reusing as much of the stock fuse panel as possible so you'll see very few add-on's in his examples. Other people have added underhood power centers and made less use of the stock fuse panel. It's really up to you, just gotta choose your path.
Joined: Mar 2001
Posts: 10,404
Likes: 2,081
Car: '89 Firebird
Engine: 7.0L
Transmission: T56
Re: How to prep a 3rd gen harness
To answer your question directly, you can cut out most or maybe all of the passenger side harness. But you'll need to put your hands on all those wires and make sure you know where they go in engine bay. Some might be critical to keep.
My Firebird had a ground wire in that bundle that I needed to keep. Actually I did cut it out and just grounded it to the interior side of the firewall instead of the engine bay side of the firewall. I'm not sure where the speedometer wires come in for the '87 Camaro, it's worth checking. The Camaro tended to hold on to older designs longer than the Firebird so some things can be different.
My Firebird had a ground wire in that bundle that I needed to keep. Actually I did cut it out and just grounded it to the interior side of the firewall instead of the engine bay side of the firewall. I'm not sure where the speedometer wires come in for the '87 Camaro, it's worth checking. The Camaro tended to hold on to older designs longer than the Firebird so some things can be different.
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Joined: Feb 2013
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From: Vancouver BC Canada
Car: 91 z28 convertible
Engine: 350lt1
Transmission: T56
Axle/Gears: 3.73
Re: How to prep a 3rd gen harness
[QUOTE=Pocket;4279270]Fuel and fan, my TBI has a single fan
Everything but the HO2s are off the heavy pink IGN wire from the C100. INJ and PCM pinks are ran thru the mini fuse box. HO2s are off the emissions
I got a 91 z28 with a 97 lt1 t56 swap.
i used the c207 connector for 2 fuses for injectors.
1 for old ecm fuse for pcm ign feed for lt1 pcm
I am left with needing a fuse for my ign 10amp and eng snrs20amp. Where can i get these?
Now do i splice a 10 amp fuse inbetween the big pink ign wire from the c100 to eng ign?
Also can i use that pink ign wire from c100 to run my eng snrs? Or should i use the emissions common on the c100?
basically if using the pink ign wire from the c100 does it have to be fused inbetween to feed power to eng snrs?
Any help much appreciated 🙏
Everything but the HO2s are off the heavy pink IGN wire from the C100. INJ and PCM pinks are ran thru the mini fuse box. HO2s are off the emissions
I got a 91 z28 with a 97 lt1 t56 swap.
i used the c207 connector for 2 fuses for injectors.
1 for old ecm fuse for pcm ign feed for lt1 pcm
I am left with needing a fuse for my ign 10amp and eng snrs20amp. Where can i get these?
Now do i splice a 10 amp fuse inbetween the big pink ign wire from the c100 to eng ign?
Also can i use that pink ign wire from c100 to run my eng snrs? Or should i use the emissions common on the c100?
basically if using the pink ign wire from the c100 does it have to be fused inbetween to feed power to eng snrs?
Any help much appreciated 🙏
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Joined: Feb 2013
Posts: 28
Likes: 0
From: Vancouver BC Canada
Car: 91 z28 convertible
Engine: 350lt1
Transmission: T56
Axle/Gears: 3.73
Re: How to prep a 3rd gen harness
[QUOTE=Pocket;4279270]Fuel and fan, my TBI has a single fan
Everything but the HO2s are off the heavy pink IGN wire from the C100. INJ and PCM pinks are ran thru the mini fuse box. HO2s are off the emissions
I got a 91 z28 with a 97 lt1 t56 swap.
i used the c207 connector for 2 fuses for injectors.
1 for old ecm fuse for pcm ign feed for lt1 pcm
I am left with needing a fuse for my ign 10amp and eng snrs20amp. Where can i get these?
Now do i splice a 10 amp fuse inbetween the big pink ign wire from the c100 to eng ign?
Also can i use that pink ign wire from c100 to run my eng snrs? Or should i use the emissions common on the c100?
basically if using the pink ign wire from the c100 does it have to be fused inbetween to feed power to eng snrs?
Any help much appreciated 🙏
Everything but the HO2s are off the heavy pink IGN wire from the C100. INJ and PCM pinks are ran thru the mini fuse box. HO2s are off the emissions
I got a 91 z28 with a 97 lt1 t56 swap.
i used the c207 connector for 2 fuses for injectors.
1 for old ecm fuse for pcm ign feed for lt1 pcm
I am left with needing a fuse for my ign 10amp and eng snrs20amp. Where can i get these?
Now do i splice a 10 amp fuse inbetween the big pink ign wire from the c100 to eng ign?
Also can i use that pink ign wire from c100 to run my eng snrs? Or should i use the emissions common on the c100?
basically if using the pink ign wire from the c100 does it have to be fused inbetween to feed power to eng snrs?
Any help much appreciated 🙏
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Engine: 5.3
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Re: How to prep a 3rd gen harness
This is very helpful I've been looking for what to do with all my left over wires THANK YOU
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Re: How to prep a 3rd gen harness
Stock gauges can be retained with a terminator kit. I make a harness specifically for this purpose
There are only four gauges in question for any swap with any setup: Speedo, tach, oil press and coolant temp
Speedo and tach are compatible with any modern EFI system. Speedo takes a standard 4,000ppm signal and tach is universal 6/8cyl
Oil is simple, just use the stock or LS sender. Holley has a three wire sensor behind the intake, but theres a second port above the oil filter that can be drill/tapped for 1/8NPT like factory. SBCs or engines without room for two senders can use a tee adapter to put both on one port behind the intake
Coolant gauge is also simple. For LS engines, the 98 fbody 3 wire CTS screws right in the cyl head. Top two wires to the CTS for the ECM, bottom is gauge sender. Alternatively, you can drill the pass cyl head port to 3/8NPT and reuse the stock sender. If can also be turned down on a lathe to 12 x 1.5mm so no drilling is needed
SBC guys can use a three wire CTS from a mid 90's FWD 3.8 V6. Same thing as LS, but 3/8NPT
Voltage gauge and fuel level are unaffected by any conversion
There are only four gauges in question for any swap with any setup: Speedo, tach, oil press and coolant temp
Speedo and tach are compatible with any modern EFI system. Speedo takes a standard 4,000ppm signal and tach is universal 6/8cyl
Oil is simple, just use the stock or LS sender. Holley has a three wire sensor behind the intake, but theres a second port above the oil filter that can be drill/tapped for 1/8NPT like factory. SBCs or engines without room for two senders can use a tee adapter to put both on one port behind the intake
Coolant gauge is also simple. For LS engines, the 98 fbody 3 wire CTS screws right in the cyl head. Top two wires to the CTS for the ECM, bottom is gauge sender. Alternatively, you can drill the pass cyl head port to 3/8NPT and reuse the stock sender. If can also be turned down on a lathe to 12 x 1.5mm so no drilling is needed
SBC guys can use a three wire CTS from a mid 90's FWD 3.8 V6. Same thing as LS, but 3/8NPT
Voltage gauge and fuel level are unaffected by any conversion
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Thread Starter
Joined: Jun 2005
Posts: 8,117
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From: NC
Car: 91 Trans Am
Re: How to prep a 3rd gen harness
When I wrote this thread years ago, speed density TPI harnesses were still in demand. MAF's were discontinued and tuning suites were tailored to the latest SD chips. These days, the tech is so old, there isn't much value in any original wiring
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