the model. Later models are missing the reverse inhibit solenoid. 88 may have 7 wires, and a three-position program selector switch.
If the car does nothing but 3rd gear and reverse, it means it is in Trans Program alarm mode. You may not have a check control module display (520i), so did not get the message, but the trans control is keeping 3rd and reverse only to prevent further damage to the transmission.
You can do a "search" in the forum looking for "Trans program" and found tons of info about this message alarm.
The 6 wires colors sorted by trans connector pins are: 1 Red, 3 White, 4 Brown, 5 Orange, 6 Green, and 7 Blue. Sorry have no info for the 7th wire.
Javier