GMT400 to LS Harness Questions

[95SUBURBANLM7]

How do you tie in the LS harness to the stock GMT400 harness? I plan on getting rid of the old ECU & DRAC, and let the '02 harness handle everything. I've read many a post and they all say it can be done, but I haven't seen it explained throughly. I want everything to work and look just like it did when it left the line in '95, so that means using the stock underhood fuse box.

Can someone help that has done this? It sure would help me and a lot of other people out there that are looking to do the same thing.

I'm using a NV4500, so there will be no need for AT controls.

Thanks for any insight.

Nick

 

[K30burb]

I have done 4 ls swaps into gmt400's. 3 of them were into 1998 trucks. one was a 1994. there are various ways to do it. depending on the truck and the final outcome you are wanting. 2 of the 98's I left the original 5.7 vortec harnesses installed in the trucks and double sensored the ls engine so the dash gauges would work and the ls was stand alone but still controlled the 4l80e's in both trucks. the 3rd 98 I did a complete wiring tear out and it only uses the ls swap harness and pcm and oe 98 under hood fuse block. the 94 truck is a bare bones race truck and uses autometer gauges so none of the oe 94 truck harness was kept.

 

[95SUBURBANLM7]

Ok, great can you share with me how to integrate the LS harness into the GMT400 harness?

 

[90W7]

My build thread is far from done but Here's my 1991 build thread if it helps in any way. http://www.gmt400.com/forum/showthread.php?t=31954

The old harness is essentially out of the equation, your only needing your oil pressure sensor/wiring, coolant temp sensor/wiring, wiper motor/wiring and the trucks original starter wiring.

You can remove all the wires from the 95 harness that go to anything on the 95 engine and transmission Exept the above mentioned and whatever wires are left can be hidden in the new ls harness loom.

You must be registered for see images attach

These wires are all that's needed for the new harness. The lower right orange is batt constant power and the rest are 12v switched power so integrating these wires to the underhood fuse block should be pretty straight forward.

The swaps are generally all the same minus small differences. I myself am not familiar with how some guys are doing the swaps on the 96+ trucks regarding the cluster wiring, abs etc.. Or even minor differences on the 95 trucks so I agree wanting a fully detailed build thread. You might have to be the one to make it [emoji1].

Hope this helps a little atleast. If you have anymore questions feel free to ask away.

Sent from my throttle body injected galaxy note3

 

[95SUBURBANLM7]

Hey man I really appreciate you replying.

1. So did you just leave the oil pressure sensor(OPS)/wiring connected to the original harness (going into the drivers side firewall)? Because from what I've heard, the LS harness and ECU does nothing with oil pressure sensor information, it's strictly information for the oil pressure gauge. If so, that's exactly what I'm planning to do. Except I believe I have to use an '04+ OPS. The '02 OPS has only one wire, whereas the '04 has three wires just like the '95. So I believe it is a straight across swap.

2. Explain to me how you set up the CTS. Unlike the OPS, the LS ECU needs the CTS information.

3. The wiper harnes seems straight forward.

That orange wire is from the GMT400 harness, correct?

You're right, I believe I'm going to have to be the one to document this building. Like I've said earlier, there's a lot of information on everything except for the LS harness to GMT400 wiring harness.

Again, I really appreciate your input. I look forward to reading more of your information.

Nick

 

[90W7]

So from the original harness you leave the:

1. Oil pressure sensor
2. CTS for the gauge
3. Alternator wiring +main power wire from alternator
4. and the 95 starter wires will attach to the new motors starter

(A) Oil press,CTS,Alt wires flipped up out of the way. And all these are JUST for your cluster. The new engine/harness could care less about these sensors, they are just for your gauges.

You must be registered for see images attach

I should of asked if you are reworking your own harness or not but i did my own following the http://www.lt1swap.com/ instructions and the Coolant temp sensor in the ls harness for the ls computer just plugs into the ls engine, no different than plugging in the injectors, coil packs, MAF etc..

You must be registered for see images attach

The issue is adapting the original single wire Coolant temp sensor for your gauge to the ls engine.

1. Either install a 3 wire temp sensor in place of the 2 wire sensor in the above picture so that the single wire for your gauge and the 2 wire for the computer share the same source/sensor (i don't know the part number for this sensor)
2. or on the right rear cylinder head there is a threaded plug you can take out and screw in your 95's single wire coolant temp sensor.

Autometer 5284 adapter kit will let you install you 95 Oil pressure sender and you coolant temp sensors into the LS motor
http://www.summitracing.com/parts/atm-5284

You must be registered for see images attach

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The orange wire is actually 2 orange wires condensed into one. these 2 wires supply batt constant to the LS computer. so for these just find a spot in you 95 fuse box that is hot always. If you rework your own harness using the lt1swap.com instructions your going to remove many wires from it that you don't need and you will be left with what you do need and the instructions are pretty good as to where they go or how they must be wired in.

You must be registered for see images attach

This isnt a very good pic but you can see a bundle of pink wires: these all need power when the key is on/during cranking
The 2 orange below it get power at all times
And there will be another handful of wires such at tach output,Vehicle speed and the data wire for the DLC/OBD2 connector( you will need to get a OBD2 connector)

 

[K30burb]

it depends on your engine/trans/pcm/tcm combo, your harness, and your truck. for most ls swaps to INTEGRATE it into a gmt400 is no different than if you are installing it into a 55chevy chassis or a Porsche 911 conversion.... usually is 3 or 4 wire hookup no matter the chassis. the gmt400 chassis is really straight forward and a easy swap. the guy above is giving you useful good info for your gauge cluster. and yes I have installed ls swaps into a 55 chevy nomad, also in 7 porsches, 4 gmt400's, 69 Camaro, rx7, and so on... they are fun and easy swaps. do your homework as most swaps are straight forward but I have not found any 2 installs exactly the same. but most of all have fun and enjoy.

 

[super10brss]

*HiJacked* 90W7 this is exactly what I am looking for! I have a 89 C1500 that I am about to LSx swap and need info on adapting the factory gauges... this is a BiG help!

 

[90W7]

*HiJacked* 90W7 this is exactly what I am looking for! I have a 89 C1500 that I am about to LSx swap and need info on adapting the factory gauges... this is a BiG help!

Yeah no problem. I've yet to do my speedo but when I do plan on taking pics and what wire needs to go to what. Your not on agearhead4life Facebook group are you?

Sent from my throttle body injected galaxy note3

 

[95SUBURBANLM7]

So from the original harness you leave the:

1. Oil pressure sensor
2. CTS for the gauge
3. Alternator wiring +main power wire from alternator
4. and the 95 starter wires will attach to the new motors starter

(A) Oil press,CTS,Alt wires flipped up out of the way. And all these are JUST for your cluster. The new engine/harness could care less about these sensors, they are just for your gauges.

You must be registered for see images attach

I should of asked if you are reworking your own harness or not but i did my own following the http://www.lt1swap.com/ instructions and the Coolant temp sensor in the ls harness for the ls computer just plugs into the ls engine, no different than plugging in the injectors, coil packs, MAF etc..

You must be registered for see images attach

The issue is adapting the original single wire Coolant temp sensor for your gauge to the ls engine.

1. Either install a 3 wire temp sensor in place of the 2 wire sensor in the above picture so that the single wire for your gauge and the 2 wire for the computer share the same source/sensor (i don't know the part number for this sensor)
2. or on the right rear cylinder head there is a threaded plug you can take out and screw in your 95's single wire coolant temp sensor.

Autometer 5284 adapter kit will let you install you 95 Oil pressure sender and you coolant temp sensors into the LS motor
http://www.summitracing.com/parts/atm-5284

You must be registered for see images attach

---

---

The orange wire is actually 2 orange wires condensed into one. these 2 wires supply batt constant to the LS computer. so for these just find a spot in you 95 fuse box that is hot always. If you rework your own harness using the lt1swap.com instructions your going to remove many wires from it that you don't need and you will be left with what you do need and the instructions are pretty good as to where they go or how they must be wired in.

You must be registered for see images attach

This isnt a very good pic but you can see a bundle of pink wires: these all need power when the key is on/during cranking
The 2 orange below it get power at all times
And there will be another handful of wires such at tach output,Vehicle speed and the data wire for the DLC/OBD2 connector( you will need to get a OBD2 connector)

Thanks for the info, lets go through it. I am reworking the LS harness per lt1swap.com. Brendan has some really great info there. Im actually gonna send him a bottle of fine Colorado ***** as a "thank you". Im reworking the Suburbans harness too, but I guess thats obvious. ;-p

I knew the ECU didnt need the oil pressure sensor (OPS), but I didnt know it didnt need the CTS or the alternator info. The OPS, I just intended on getting a three wire OPS that would fit in the stock spot without any adapters. If I cannot find that sensor, Ill just buy the Autometer part. Thanks for the part number! After that I was going to take the OPS wires and connect them to the GMT400 harness at the bulkhead in the firewall on the drivers side just below the brake booster. I read the pinout and didnt see a spot for it. Which wires do I connect the OPS wires to?

Sounds pretty straight forward for the CTS. I guess I will go the route of installing the old CTS in the right side port. I believe that will connect to a yellow wire (B8 from the red GMT400 ECU plug)?

The alternator wire, I cut it out of the GMT400 harness and am using the LS harnesses alternator plug. This is per Brendans instructions on lt1swap.com, so I believe it is right.

You answered my question that I had regarding the orange and pink wires. In the GMT400 pinout, it called pink "Ignition Feed", and orange as "Battery Feed".

Again, much appreciation for your help. You're info is helping me get my project finished before the snow starts flying!