Very stimulating questions, Al. I know some of the answers.


Was 89 was the first year for the silly 5K miles service reset light hence the difference between 88 and 89?

I like that silly light. Trouble is, the return spring post is busted on every one I see. Having daughters, I like it to work, although I try to put a sticker on the windshield to have the same effect. Red lights are more attention-getting. But no, I don't know when that kicked off. The '89 New Car Facts book only makes mention of two speedometer improvements; the matte finish and the red tenths digit for renewal parts.

Did 1991 used the same speedo as 1990 but need a signal conditioner to reduce the tone ring signal by 4 to compensate for the 48 vs 16 tone ring where 1992 and 1993 went to a different speedo.

Exactly. And if you happen to run across an ABS 91 in the yard, grab that little module. At least twice a year some unhappy volvoist writes on the brickboard "help, I got a new rear axle from a later car and now the speedometer is wrong." You'll be able to help him a lot cheaper than Dakota Digital, or rewiring the cable to accept the 92+ version gauge.

Looking at my 1990 wiring diagrams it looks like the VSS signal feeds both the ECU and the cruise control module. Seeing that the 1990 and 1991 use the same ECU I would think the output is the same.

Yes, the output to the ECU is the same 89-93. It is a very fast pulse for an LED test light to catch. Maybe in the dark? About 2 mS if I remember the scope trace. Will set DTC 311 if missing and cause idle all over the place, or so I hear.
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Art Benstein near Baltimore

Accept that some days you're the pigeon, and some days you're the statue.