I believe the plug on the 89+ harness is just black. There is no pigtail on the CPS side, the connector is built into the CPS housing. You could cut the end off of the '91 harness and wire in the end from the '87 harness.
Is there a reason your harness can't be rebuilt? Toyota does still sell many of the replacement connectors for it. It is a lot of work, but I don't know how bad it is... It may end up being just as much work to convert and swap a later model harness.
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