Author Topic: 90 Tbi swap into 85 K10 wiring help needed  (Read 791 times)

Offline Oldsarge29

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90 Tbi swap into 85 K10 wiring help needed
« on: November 16, 2021, 07:02:06 PM »
Hi all,
I知 currently swapping a 90 tbi engine into my 85 K10 and I知 down to the wiring part. I have the complete donor truck and I have pulled the complete wiring harness and ecm to use in the 85. I have the engine completely installed. I知 waiting on a new fuel tank, pump and sending unit. I値l complete the fuel system when I get those parts. I知 not that good with wiring but I can follow instructions and wiring diagrams. I知 pretty sure I have the wiring figured out for power and grounds. The ecm is a 1228747 with a AKWA eprom. Nothing else is readable on the ecm. I知 pretty lost on how to connect the new harness to the existing gauges. Any help will be greatly appreciated.
Oldsarge29
1985 Scottsdale
1985 1008 Military CUCV truck
1985 1028 Military CUCV truck

Offline bd

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Re: 90 Tbi swap into 85 K10 wiring help needed
« Reply #1 on: November 17, 2021, 03:28:43 PM »
Put the wiring diagrams for the 1985 and 1990 side-by-side.  Compare the I/P cluster pinouts between the two and repin accordingly.  The basic color codes between those years should be nearly identical, but there are important differences, such as the vehicle speed buffer and VSS from the speedometer head on the TBI-equipped vehicle.  The ECM requires a VSS input either from the speedometer or a VSS generator tapped off the speedometer cable. 
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Oldsarge29

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Re: 90 Tbi swap into 85 K10 wiring help needed
« Reply #2 on: November 19, 2021, 06:21:37 AM »
Thanks for the help. I hadn’t thought about comparing the 2. I guess I was overthinking the whole thing.
Will the vss signal from the 85 work with the ecm from the 90 or do I need to get something else to make it work?
« Last Edit: November 19, 2021, 06:25:01 AM by Oldsarge29 »
1985 Scottsdale
1985 1008 Military CUCV truck
1985 1028 Military CUCV truck

Offline bd

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Re: 90 Tbi swap into 85 K10 wiring help needed
« Reply #3 on: November 19, 2021, 10:01:25 AM »
Dash Cluster Pin Diagrams is another reference that may help.  Our Technical Forum has a comprehensive selection of OEM Service and Wiring Manuals.

The 1985 model trucks had no VSS; there was no need.  Either pick up a later model (1987-1990 R/V) cluster that has the cable-driven speedometer with integrated VSS and external buffer or fit a VSS generator onto the transmission end of the existing 1985 speedometer cable.  Jags that Run used to supply VSS generators that retrofit nicely.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Oldsarge29

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Re: 90 Tbi swap into 85 K10 wiring help needed
« Reply #4 on: November 19, 2021, 04:10:21 PM »
I thought that the 85 with cruise control had to have a vss signal to control the speed. That痴 what I was thinking about using for the ecm input. Am I wrong?
1985 Scottsdale
1985 1008 Military CUCV truck
1985 1028 Military CUCV truck

Offline bd

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Re: 90 Tbi swap into 85 K10 wiring help needed
« Reply #5 on: November 19, 2021, 07:16:06 PM »
You are correct.  Custom Cruise III used a VSS speedometer with buffer that should supply signal to the ECM.

Custom Cruise III Manual
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline Oldsarge29

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Re: 90 Tbi swap into 85 K10 wiring help needed
« Reply #6 on: November 28, 2021, 07:17:50 AM »
I have the engine in and running. Everything seems to be working as it should right now. I still need to do a test drive. I have a purple wire that comes from the 3rd plug (white) near the ecm that is in pin L and I can稚 figure out where it goes. This wire has a resistor inline and splits into 2 wires and both go back into the harness. The other problem is I知 working on the speed input for the ecm. My truck has the optical sensor in the speedometer and I found the speed buffer. I haven稚 been able to figure out what wire I need to use for the input to the ecm. The ecm is out of a 90 2500. Any information on this world be greatly appreciated.
1985 Scottsdale
1985 1008 Military CUCV truck
1985 1028 Military CUCV truck

Offline Oldsarge29

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Re: 90 Tbi swap into 85 K10 wiring help needed
« Reply #7 on: November 30, 2021, 04:55:16 PM »
Bump.
Anybody have any information on this??
1985 Scottsdale
1985 1008 Military CUCV truck
1985 1028 Military CUCV truck

Offline bd

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Re: 90 Tbi swap into 85 K10 wiring help needed
« Reply #8 on: December 02, 2021, 12:08:31 PM »
The attached image should supply a key piece to the puzzle.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)