Yes, glad to see this, mine also looks factory except for the added connector w the red insulator.
I have studied further Sheet 5 of the 1989 Wiring Diagram Model 89. It shows the OB switch as “charge air pressure indicator switch”. It shows two WT wires leaving the switch, one travels to the “speed relay” and enters on the 7000 1/rpm side. I assume that is the rpm limiter which cuts the fuel pumps when 7000 rpm is reached.
The other WT wire runs to pin 7pin of a connector that has pins numbered up to 14 at T69. Don’t know what the T69 reference means, probably a physical location n the car. Guessing its the 14 pin connector that plugs into to back of the fuse/relay panel in the back left of the engine compartment where the YELLOW relay lives. From there the WT wire travels to pin 86 of the “Relay Air Meter Charge Air Pressure Delayed” relay. When this relay closes it connects pin 87 to pin 85 of the “Relay Fuel Pump II” thereby grounding it and causing it to close along with “Relay Fuel Pump I” which is slaved to II.
This all seems to jibe w what has been said by others (908/930 in particular). However, my OB switch has only one WT wire leaving the switch and looks to be the original wire, connectors and harness sheathing. I have looked under the drivers seat and can see no obvious mods to the wiring. I will have to remove the seat to look more closely. I think my next step is to see if the WT wire I have is the one that goes to the speed relay or to the 14 pin connector in the engine compartment.
I will test for continuity between WT wire i have and pin 7 of the 14 pin connector. If I have continuity there, there must be a break between there and the air meter relay. Not sure where that relay physically lives.
It appears my engine compartment main harness has been mucked with at some point, its is wrapped in electrical tape. It’s about 1” in diameter in the area behind the distributor going towards the relay/fuse panel. So its anyone’s guess what changes have been made. I’d like to get the whole mess back to stock but not sure its worth it just to get the OB switch to work as designed.
I’m in the middle of fitting the new vacuum canister and running into a problem with interference between the canister (which is maybe a half inch taller than the OEM canister) and the engine tin underneath. It prevents the canister from rotating fully clockwise to the end of the adjustement slot.
I may end up cutting the tin to provide clearance but would hate to do that. The oil feed for the turbo is not centered in the tin and the hole is offset to the right (see pic).
Not sure the best way to correct this.
As always, thank you for the assistance.