88 square body

[rangokatt]

I'm buying a tbi 454 and th400 from a 88 square body and plan on dropping in my truck in the picture also 88 will I need to find a harness for my truck or can I use the square body harness since they are both 88

 

[GoToGuy]

Did yours have 454 ?

 

[rangokatt]

Did yours have 454 ?

Naw 5.7

 

[someotherguy]

I'd go ahead and get the harness from the donor truck, but it's not going to be a direct fit into yours. The squarebody and GMT400 harnesses aren't the same. However, with studying the wiring diagrams of both from the factory manuals (you'll find your truck's manual here in the forums, sticky post in this section - the squarebody can probably be found online, too) you should be able to piece them together as needed.

If you wanted to find a factory GMT400 harness that would fit your truck it would have to come from a 2500 or 3500 truck with 454/TH400 which would be 1988-1990. (or of course a 1990 454SS harness)

Richard

 

[GoToGuy]

I agree with that plan. Will the computer be compatible with big block?

 

[rangokatt]

I agree with that plan. Will the computer be compatible with big block?

I'd go ahead and get the harness from the donor truck, but it's not going to be a direct fit into yours. The squarebody and GMT400 harnesses aren't the same. However, with studying the wiring diagrams of both from the factory manuals (you'll find your truck's manual here in the forums, sticky post in this section - the squarebody can probably be found online, too) you should be able to piece them together as needed.

If you wanted to find a factory GMT400 harness that would fit your truck it would have to come from a 2500 or 3500 truck with 454/TH400 which would be 1988-1990. (or of course a 1990 454SS harness)

Richard

I'd go ahead and get the harness from the donor truck, but it's not going to be a direct fit into yours. The squarebody and GMT400 harnesses aren't the same. However, with studying the wiring diagrams of both from the factory manuals (you'll find your truck's manual here in the forums, sticky post in this section - the squarebody can probably be found online, too) you should be able to piece them together as needed.

If you wanted to find a factory GMT400 harness that would fit your truck it would have to come from a 2500 or 3500 truck with 454/TH400 which would be 1988-1990. (or of course a 1990 454SS harness)

Richard

The one I'm getting is gonna come with harness computer and cruise control module I'll probably try to find one for the truck it will definitely be easier to swap out the whole thing especially with the engine out

 

[GoToGuy]

Good plan.

 

[L31MaxExpress]

What is wrong with the current harness in the truck? Seeing yours has 8-lug wheels, I am assuming it had the HD 350 and TH400 from the factory. 454 should be near plug and play, swap the ECM and go. Both the HD350 and 454 ran the 8747 ECM as they both used the EVRV EGR solenoid. As such only really need to swap the Calpack and PROM chip, but if the 454 currently runs it is easier to just slap the 454 ECM in. Some of the early 454s did not use a knock sensor, but the ECM is programmed for its absence and will not care that the knock sensor wiring for the 350 is zip tied out of the way.

If you have a TH400 already and it is operating well, I would not even remove it from the truck. Put a heavy ratchet strap across the frame, suspending the front of the TH400, unbolt it from the 350, pull the 350 and slide the 454 back in.

 

[rangokatt]

What is wrong with the current harness in the truck?

It's for a 5.7 and in some spots rats have gotten to it

 

[rangokatt]

It's for a 5.7 and in some spots rats have gotten to it correct the stock transmission is a th400 but it got stolen so I'm buying a th400 with 454 setup