[rfmaster]

Originally Posted by glock35ipsc

Great thread! I have two quick questions, if I may:

1) I might be getting a 91 dually with a TBI 454. Is the TBI harness that is needed for a swap a stand-alone harness, or are the parts of the harness needed part of a larger harness?

2) The 85 I am getting (avatar pic) already has had a 350 TBI swapped in with donor parts from an 87. If I put the 454 TBI motor in the 85, will the existing harness suffice? I am guessing I will need to replace the ECM with the one from the 454 truck though.

Thanks in advance!

1) The early OE TBI harnesses, up to about '94, were more or less stand alone across most GM products. In later years additional functionality, notably AC vacuum controls, was integrated along with TBI harness in passenger cars. For the most part trucks used stand alone harness. The biggest hick up with OE harness retrofit can be with the under dash interface - ALDL connector, DRAC I/O (or VSS) and power. Engine compartment difficulties are usually are around Fuel Pump wiring, but this is an easy fix.

2) SBC and BBC harnesses are nearly identical with few exceptions:
a) BBC used different IAC motor and connector is different - four wires.
b) TPS may be different, early BBC used lever style TPS adjustable, while later used throttle shaft style - similiar to cars. Different connector.
c) Some HD BBC did not use knock sensor (KS) and ESC modules - these engines used 1228747 ECM and can be positively identified by broadcast code printed on ECM label (four letter code).

2-1) You'll have to use 454 TBI ECM with your swap to keep things easy.

In general 1227747 ECM (when loaded with appropriate BCC EPROM) was used with V6 (4.3L) and 305/350 SBC V8 and some 454 BBC. The 1228747 ECM has identical harness interface minus KS functionality for HD application. You can swap out your SBC 7747 ECM for 8747 when you perform the swap. Other than aforementioned points 2a and 2b SBC harness is good to go.

//RF