A long while ago I posted this problem with my shift up light. I just cant seem to figure it out why it comes on when I am cruising on the highway in 5th gear. I checked the switch at the tanny and it seems to be making connectivity through the wires when in 5th gear.


Does anyone think my switch on the tranny is bad? Maybe it is weak.

Can I just short the 5th gear wires to test this crap out or what?? Maybe I can make a temporary fix by using an external switch mounted inside??


Other problem may be a broken wire somewhere on the computer harness at which point I have no clue how to fix or find.

 

Pin 1I on the ECU is how the ECU knows you are in 5th gear or not. If you are, ground should appear on this pin. Otherwise, 12V should be there. If the 12V does not, check the black/blue stripe wire at the 5th gear plug. It should have 12V. If it does, you have a break in the wiring to the ECU. It comes from the split air solenoid valve in the ACV.
If the 12V is there, but it does not ever go to ground, to the check for 12V at the connector again. If it is not there, you have a wiring problem from the ECU to the connector. If it is there, check the switch in 5th gear. It should be a short. If it isn't replace the switch. If it is, repair the ground wire on the other pin of the connector.

Irv, Keith's dad

 

ok so where is the loop? where are these 2 wires comming from? One is comming from the ecu, pin 1I, and the other wire is grounded??? Where is it grounded again?

I have read a few things about the switch getting dirty and it not having a good connection, i hear some people put a relay in there cause a gummed up switch still has a little bit of continuity left in it. Does this sound like an idea for me?

 

The over the top switch has two wires.
One wire is BLACK. It is the ground wire and goes to a grounding block next to the trail coils and main relay.
The other wire is BLACK WITH A BLUE STRIPE. That wire goes to pin 1I.
The BLACK WIRE WITH A BLUE STRIPE, also has a wire spliced into it. That wire goes to the SPLIT AIR SOLENOID ON THE AIR CONTROL VALVE. In getting there, it passes thru a connector and the wire turns from a BLACK WIRE WITH A BLUE STRIPE, to a pure WHITE wire on the SPLIT AIR SOLENOID.
That WHITE wire has 12v on it from the coil on the split air solenoid.
The over the top switch is open unless you are in fifth gear.
So you will see 12v on the BLACK WIRE WITH A BLUE STRIPE, anytime the switch is not made.
If the over the top switch is made, you have a path to ground which will result in a voltage of less than 1.5v on the BLACK WIRE WITH A BLUE STRIPE.
It helps to have the schematic downloaded to your hard drive. That one one the web that is free for a 88 will do fine for a 87 also. It just makes sense when you look at the diagram compared to someone trying to explain it. A combination works best.