Hoping to acquire some of the vast experience present on this newsgroup.
Here's the problem: I gotta have a tachometer. Don't like to drive strictly by ear. So, I went to my local salvage yard and found a '79 244, 4 spd. with a tachometer. Carefully pulled said instrument cluster and brought home new car object and carefully removed tach from salvage unit and cautiously installed into my cluster. Installed my cluster back into my vehicle. Tach doesn't work. All of my idiot lights work and both the gas and water temp. gauges work marvy. The date of manuf. on the back of my cluster is two months later than the donor cluster. Salvage tach unit has three connections on the back. One is positive and another is negative and the third is marked 1. There wasn't a lead connected to the 1 terminal when I pulled it and I don't have any "leftover" wiring in the dash of my vehicle. Both circuit boards on the backs of the clusters matched exactly (Nothing on one that wasn't on the other). I might add that the speedometer in my vehicle was causing me to want to kill many of my fellow motorists. They seemed to be driving just under (5-7 mph under) the posted speed. Since I drive the same route to work very day and previous to owning this Volvo, I only infrequently thought of dismembering others, I suspected something amiss. So, I checked my speedometer against some milepost markers and found that * I * should be the dismembered motorist. My speedometer was reading 6-7 mph slower than actual mph. Someone in my vehicle's past replaced the speedo. and wasn't cognizant of the different ratios printed on the face of the gauge cluster. This wouldn't make a difference in the tach's operation, but it could be a useful detail. Or not. I would greatly appreciate any insights others on this group might have.... Take care, Basaltrock