Maybe I'm reading this wrong, but everything that connects to the '89 5.8 computer, needs to be from the '89. The harness that wraps around the engine bay, is the engine harness.
Earlier in the thread, when you referred to "cab harness", versus "engine harness", I thought you meant radio, dash lighting, gauges, etc.in the '90.
The O2 sensor wiring needs to be 3 wire, as it was in the '89 truck, if you're using the '89 computer.

 

I'd start with 2 PCEDs and 2 EVTMs
I have a 90 evtm and a 89 PCED
Your best bet is to hit the library and use their AllData for free
On AllData you can get all the pinout diagrams
You should be able to make it work

 

What if I bought this pcm and use the 4 wire 02 and keep the grounds on the rad support wouldt that work and save me from having to change anything around

 

It's not the computer that is different for a 1989 model year versus 1990. It's how the wiring is routed and connected to achieve the overall same functions. The O2 Signal still goes to Pin 29 on the computer for a three or four wire O2 sensor. The listed HEGO signal ground is still Pin 49 for both. The return paths are the difference. A three wire O2 sensor has the signal return tied to G802 on 5L/5.8L gas engine trucks under 8500# GVW. Pin 49 is tied to G711. G711 and G802 are electrically the same point, but susceptible to electronic noise. On a 4 wire O2 sensor the signal return is a dedicated path back to Pin 49 with a splice to ground G103 (5L trucks) or G100 (5.8L trucks).

A three wire O2 sensor uses the case to provide a ground for the heater circuit. A four wire O2 sensor uses the fourth wire as a dedicated path to ground for the heater.

When you swap in the 1989 engine harness and engine verify the the signal path and return for the O2 sensor signal is good. The same for the heater circuit. Move on to the next issue.

An EVTM for a 1989 and 1990 model year truck/Bronco will help with your swap.

 

**** seems like a lot so could I save that head ache by just swapping the engine bay harness to the 89 instead of the 90 so it will be the 89 from the pcm out to the engine bay only harness from the 90 then would be the one behind the dash does the harness diconect from the white plug that’s shaped like a cone next to the pcm plug on the fire wall

 

Sorry if I sound dumb I just have no clue what I’m doing when it come to wires so if there is a way I could I avoid that but just taking the complete engine bay harness and using that I rather that but the89 engine is in and runs rough due to no 02 sensor I’m guessing but ya thank you guys so much for your time really appreciate it

 

Also What do you guys think about this set any good for what I need

 

What’s up guys I’m running into another issue so I replaced all my tanks , fuel pumps and filters everything is new and the pump will prime but will not stay running when the engine starts and causes it to die when it died I check the valve on the fuel rain and fuel just spilled out just alittle shouldt it have shot out and held pressure the for sure regulator is also new what do you guys think any test I could do to rule stuff out ?

 

why would I need the 89 fuel pump harness if I’m going to use the 90 pumps is the wiring different would the 89 wires run the 90s pumps with out the frame mounted pump connected asking because I got eveyrhign hooked up using the 90 fule pump harness and the rear pump won’t turn on only the front pump primes no matter the selector switch location of front or back the front still primes but it won’t stay running either it will prrime but won’t pump fuel as the truck starts

 

You need the books and the diagrams, not the actual wiring for the 89
The wiring you might need will be the selector switch wiring
Yes, all that wiring will be different

 

couldt I just buy a 1990 computer for my engine and trans and use that with the 1990 complete harness and go about it that way would that work ?

 

A 1990 computer is not going to fix your issue. The computer is programmed to energize a fuel pump relay. It has no idea if there are one, two or three fuel pumps beyond the relay.

 

The processors might be close to the same
With PCEDs from each year and EVTMs you could be sure of the pinouts

 

ya but it’s as if I took an engine out of a 1990 and droped in the 89 engine in the engine harness would be the same all That would be different is the block it self or am I crazy to think that would that solve the issue of chasing wires and all that other ****

 

the 1990 had 2 pumps already so it not like I have to add one on it just seems the 1989 engine bay harness is different some where going back towards the fuel pump Harness when I had the 1990 harness hooked up the pumps worked im pretty sure going to double check that but seems once I put swaped the 90 engine bay harness to the 89 and kept the harness in the cab the 1990 it seems somthing dosnt match idk what els would cause one pump to run and even when hitting the switch it stays on the front and pushes fule back to rear