from a mid model (1987/88) 240... SCU (my own made up abbreviation) is the shifter control unit.

unswitched power via fuse 9, green-white wire goes to SCU pin 30.
black wire, ground to SCU pin 31.
brown wire from clutch switch goes to SCU pin C.
orange wire from instrument panel (IP) pin 31/4 to SCU pin 0D (this is the 5th/OD light).
white-red wire from IP pin 68(?) goes to SCU pin 1 (this is the coil wire to the tach and cruise control).
yellow-red wire from IP pin 34 (uparrow light) to SCU pin L.
blue wire from IP pin 228/200 (speedometer) to IP pin "G" (6?)

the drawing also shows ignition switched power from the ignition key pin 15, red-black wire, to IP pin 233/3, this is the main instrument panel power via the speedo connector

 

"actually, OE on the manuals, the 5th light comes on..."

pierce +1.

I never had any rust issues near the windshield, though there is a place underneath that is making me a little nervous.

As to wiring diagrams... on post #3 of this thread, I put up the 85 and 91 wiring diagrams... let me check again and see what year yours is... Oh, 86? Well, I think you should have an 5th gear light in your console.... let me double check... yeah, the wiring diagram for 86 looks the same as the one I posted.

So... you got a wiring harness out of a '92? I'm guessing out of an automatic? Here is the thing... the wiring harness for an M46 has sort of a double end that heads over to the instrument cluster area. One end is to hook into the instrument cluster, and I forget everything it does, but I think it provides power. Oh, yes it does, it is "j" in the wiring diagram. It also lights up your light. There is a second connector that hooks up to your system that is supposed to light up your light that tells you when to shift.

The wiring harness out of an automatic does not have the same ends--rather, it only has one, since obviously, you don't need help to know when to shift. But, there are some changes--with only one end, what used to light up your 5th gear light, now goes to a different pin and lights up your OD off light, and it functions backwards... which I think is consistent with what you are experiencing.

Now... I didn't bother putting in the shiftier assistance relay/light on my car. It seemed like a hassle for something that would only ever annoy me. So, that's why I don't make any real reference to that in my thread. But, if you hook the correct wire up to the 5th gear light, it should just plug and go. Check the bulb, though. If that is out, it is an easy fix. The issue I was dealing with is my car (a 91) doesn't have that light... so I have to rig up something if I ever want one. (Still haven't).

Edit: And while I was writing, pierce has struck again. but this may be helpful too.

 

one thing bugging me, I can't find the wiring for the OD relay on the stickshift cars. its definitely different than the automatic OD, there should be a switch in the tranny indicating its in 4th to disable the OD in any other gear.

 

pierce--You are right about that. And this is kind of important--under no circumstances do you want to be in OD when using reverse. It will destroy your tranny.

Okay, here is the diagram for the '85 manual m46.



And here is the diagram for the automatic.



If you compare the two, you can see the differences. that is why I did not use an automatic harness, but kept the one that came with the transmission.

So, bumblebeeman, right now you probably don't have anything wired up to switch G in the diagram, or did you rig up something? How have you wired it up?

 

Oh.... this



may be what you are looking for pierce. the numbers on it correspond to the numbers on the above diagram... but this is for the manual. The "85" terminal is the key difference between the relays.

 

Haha my poor sate-light can barely handle the bandwidth, i need to try cleaning that thing. No no sorry for the confusion i got my harness from a 92 that was a manual. i left most of the auto one in place besides the neutral safety switch, i got a jumper from the manual I had one extra yellow wire that i hooked up to a pin on the console just by the orange up arrow. when i am driving the arrow is on, when i turn on OD, arrow turns off. i want to fix that. Eventually. I do have a console with the green 5th light in it... the PO was collecting lots of old volvo things. It only comes on in 4th.