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TBI Wiring Harness Conversion !

First you need to go to junk yard and pull the engine EFI harness or complete system if you can. There will be a lot of extra things, don't worry about them now grab it all as whole as you can.

Couple things under dashboard are going to be near impossible and get all of, one is wire to VSS sensor if it is in the speedometer. Another is wiring to ALDL port, grab as much as you can and cut, we'll get it all connected later. One wire goes all the way to fuyel tank for EFI fuel pump grab as much as you want.

Pin by pin on the 1227747 harness is listed below but you should really have a set of diagrams. We have them all big enough to print out here:

Lay the harness out on your work bench and have each sensor plugged into the harness, then trace each wire back to the ECM connector, you will be able to separate a lot of uneeded wires, consult wiring diagrams.

Once you have each wire identified and layed out, then you can set it up on the engine and start tailoring it to fit your engine.

Placement of the sensors will determine wire length. Most stock harnesses are plenty long and only need to be shortened or wrapped and bundled. Use good wiring practices here, crimp connectors are just going to fail someday, solder or use connector without plastic cover and slightly crimp to hold wire in place but then solder. Solder and shrink wrap are permanent.

When it's all done and it's running go back and reinstall the plastic loom over all the harness.

Basics to Conversion wiring:
I run 2 relays. 1 for 12v to the ignition, ECM power and injectors, and 1 for the fuel pump. I use the basic 30 amp aux lighting relays from the parts store. If the harness came with the factory fuel pump relay than I retain that relay. If not I use the 2nd 30 amp relay for the fuel pump. Both relays are energized from the 12v ignition wire that used to go to the + side of the coil. Since it is only used to turn the relays on there is less draw on the stock 30 year old scout wiring.
I don't run the ign from the switch. Due to voltage drop from the old IH wiring. I run all switched(from the key "on" position) 12vdc thru the relay.

If you use a bosch style relay here are the pins:
There are several different versions of the relay out there so look at the pin numbers before you buy one.

30-12v fused input(should also hook up your org ECM constant 12v to this wire)
85- Gnd
86- 12vdc from ign sw(black wire that was hooked up to the coil +)
87- pink/blk, pink(ignition, ecm power)
87- red, white(injectors)

there are 2- 87 output terminals on the SPST 5 terminal relay so you can use both.

Using factory relays like fuel pump relays are cheap and easy....
Did you print them yet? Ha!

Pin A comes from the ECM pin A1 and is used to apply 12V to the relay to turn it on.

Pin C is the ground wire. Can be connected to one of the black/wht wires.

Pin D is your 12V from a fuse. This is normally tied to the org wires B1 and C16. It is the same that provides the bat 12V to the ECM.

Pin B is the output of the relay going to the Fuel Pump or any other load you have connected to it.
This also ties to pin B2 of the ECM to tell it when the FP is actually running.

Now the pin letters may not be exactly the same as this diagram. That's not important. If you follow the diagram here and the description and just match it up to the diagram on your relay!!!


There are 2 connectors. If you look really close you can see they are labeled. The small one is A & B. The large one is C & D.
There are also numbers on the plug for each pin.

Here's a list of the pins but they are also on the wiring diagrams above.

A1- grn/wht- this wire is used to energize the fuel pump relay.
A2- not used
A3- not used
A4- gry- to EGR relay.(optional) This is a ground from the ECM to control the EGR relay.
A5- brn/wht- SES(service eng soon) light. This is a ground to turn on the light.
A6- pnk/blk- switched 12v from the ignition relay.
A7- not used
A8- orn- ALDL Serial data. This is your ALDL pin E data for your lap top.
A9- wht/blk- ALDL pin B diag mode. When jumpered to ground will set the ECM to ALDL diagnostic mode.
A10- brn- VSS speed sensor signal to the ECM (optional)
A11- ppl or blk- MAP sensor ground.
A12- blk/wht- System ground. Can be tied with D1. Goes to engine ground.

A11 and A12 are also solder connected in ECM. Use them all as grounds or you risk grounding issues. GM did not add these because they are not needed. Some guys make short cuts, don't mess with perfection!

B1- orn- 12v fused from battery. Use an inline fuse on this. It also ties into C16.
B2- tan/wht- Fuel pump signal from the relay. This one ties into several places, the fuel pump, the relay, and the ecm. When the relay is on it sends 12v thru this wire to turn on the fuel pump, at the same time it tells the ECM the fuel pump is on.
B3- blk/red- EST reference.
B4- not used
B5- ppl/wht- EST high reference
B6- not used
B7- blk- ESC signal This is the knock sensor signal to the ECM. There are ways to run without Knock Sensor circut but it is a good option, can save your motor and great for tuning!

If not used, tie this wire to C14 the 5v reference. This will fool the system sometimes but you will need to program the chip to prevent the SES light from coming on.

B8- dk grn- AC signal. This tells the ECM that the AC is turned on. Just tie it to the wire going to the AC clutch or on board air compressor or winch etc...
B9- not used
B10-orn/blk- Park/Neutral switch tells the ECM if in Park Or driving. Manual trans does not have this wire.
B11- not used
B12- not used

C1- not used
C2- not used
C6- IAC -The ECM controls the IAC motor. It adjust the amount of air that is bypassed around the butterflies to adjust the idle speed.
Note: For the IAC pins C5 and C6 are reversed on the 454 vs the SBC so swap those 2 pins if using a 454 TB with the bolt on IAC.

C7- not used
C8- not used
C9- ppl/wht- Starter crank signal. Goes to the small terminal of the starter. Tells the ECM you are trying to start the engine. Hook to starter wire that is hot only when key in crank position.
C10- yel- Temp sender signal
C11- lt grn- Map sensor signal
C12- Not used on 1227747 but is IAT on 1228746
C13- dk blu- TPS sensor signal
C14- gry- 5v reference signal to map and TPS.
C15- grn- inj B ground signal.
C16- orn- fused 12v tied to B1

D1- blk/wht- System ground, ties to A12 and engine.
D2- blk- Sensor ground. To eng block or head.
D3- not used
D4- wht- EST control
D5- tan/blk- EST bypass. This is the wire that has a plug near the distr that you disconnect to set your timing.
D6- Tan- O2 ground to engine.
D7- ppl- O2 sensor signal
D8- not used
D13 not used
D14- lt grn- Injector B ground signal
D15- blu- optional injector A ground signal
D16- blu- Injector A ground signal

These pages will always be updated with new information ! For more information check out links to forums.

Written by EagleMark and Members of

Copyright 1999 2012 TBI and EFI wiring and diagrams for EFI conversion!