I was trying to find proper wiring diagrams to help follow your shift indicator problem. The manual transmission shift indicator doesn't seem to be well covered in the green manual electrical wiring diagram, but I finally found something in the OzVolvo technical archive that may help with your troubleshooting and the discussion here in case you need it. This 1985 manual is as close as I can come to your 1989. Your wiring should be similar.
Download TP30808-1 Volvo Service Manual Wiring Diagram (Fault Tracing, Repair and Maintenance; Gr. 39), 1985 Model 240,260 (35.6MB)
(you may need to hit that link a couple of times or copy/paste it into your browser to get it to work or type the TP number into the OzVolvo search field)
The Gear Shift Indicator (manual trans) is covered on pages 111-112 (the pages aren't numbered)
The Combined Instrument Cluster (VDO & Yasaki) is covered on pages 103-104

I like your thought about that loose blue wire at instrument cluster connector 32/6 that you're pursuing at the time of my writing here. If that doesn't pan out then my tendency would be to go back and use a meter to re-check things and see if you can isolate the problem a bit better. Looking at the 1985 schematic, it's that Y-R wire shown on the single spade connector (#34) on the back of the cluster that I'd want to make sure is okay, that the ECU is trying to pull that signal to ground to illuminate the lamp and that the traces on the circuit board near that spade connector aren't cracked. On your 1989, from what I can tell, that will be a violet wire that goes from connector 34 to ECU connector pin 26. If you're probing at the ECU connector, be sure to probe at the side of the connector to prevent contact damage.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now

Hi Matt,

You've already done everything I can think of, so the only suggestion I can offer is to go over what you've done since replacing the light bulb. Otherwise, I stand to learn something from your mystery when you solve it.
--
Art Benstein near Baltimore

"It's so much darker when a light goes out than it would have been if it had never shone." John Steinbeck

Hi,

Maybe the shift up program works from a signal from the ICU and not the speedometer.
The ICU communicates with the ECU for timing variations in program for coolant temperature and knock sensor adjustments.

I say this because, when mine worked on my 1986 wagon, with the MPG option!
It did seemed to be RPM and LOAD sensitive.
Its ICU has a vacuum diaphragm to sense loads.
The 1989+ got a different EZK and CPS system that sits side by side under the glove box.
I’m sure they are hugging and snuggled up to work together.
I’m surprised to hear that the MPG feature was continued into 1989!

When observing the light it seemed to be RPM related but I would noticed a few seconds of lag variations, so it moved the shift point around a little bit if I played with the pedal!

The light indicated a shift when I was still interested in going up to the next gear with some momentum, so it would not feel as if I would be lugging a little.
The system was lacking some sensibility to compensate for a grade going up on the increase or the car being loaded differently.

I considered the whole thing as a nuisance feature and took the bulb out! Tape works too!
I still don’t care fir service reminders lights built on mileage only.
By the nineties we got blessed with a cursory or cussed at “CEL” that scares people off their wallets for smog inspections.

Later on they went to making ECU programs to “adapt” to a drivers habits. Supposedly to raise mileage ratings but it came with its baggage of learning quirks for those engineers.

Happy hunting the diagrams for that signal wire!
It’s got to have one or two because of the CPS system.

Phil

Check owners manual. There's a procedure to re-calibrate the upshift arrow by driving it.
--
Post Back. That's whats makes this forum work.