The dash mounted tachometer is a well-known, sought after, distinguishing feature of the 123 GT.
Manufactured by Smith in the U.K, the instrument is scaled from 0 to 70 in increments of 10, with a dashed red-line at 60 and full red at 65 (i.e 6500 rpm). The silk-screened dial attaches with 2 small screws. The instrument has an orange indicator needle and a chrome bezel. George Minassian's site provides a part number: 281046.
The dial inscriptions say:
The housing itself has a rough, "pebbled" surface. It sits upon on a threaded plastic stalk which tightens an asymmetric footpad onto the 123's padded dash, just left of the shelf. For those adding a tach to a 122 to emulate a 123 GT, the correct position of the hole in the dashboard which accepts the stalk is shown below:
The 123 GT has 5 wires: two white, two red and one black.
Manufactured by Smith in the U.K, the instrument is scaled from 0 to 70 in increments of 10, with a dashed red-line at 60 and full red at 65 (i.e 6500 rpm). The silk-screened dial attaches with 2 small screws. The instrument has an orange indicator needle and a chrome bezel. George Minassian's site provides a part number: 281046.
VOLVO
SMITHS
RPM x 100
4 CYL
NEGATIVE EARTH
RVI5411/OOA MADE IN U.K.
It took me awhile to find the correct one in good shape, with all the proper wires and an intact stalk. Even then, I had it gone through by Bruce Abbot, to clean it up and calibrate it.
The housing itself has a rough, "pebbled" surface. It sits upon on a threaded plastic stalk which tightens an asymmetric footpad onto the 123's padded dash, just left of the shelf. For those adding a tach to a 122 to emulate a 123 GT, the correct position of the hole in the dashboard which accepts the stalk is shown below:
The 123 GT has 5 wires: two white, two red and one black.
The white wire with the black rubber sleeve attaches to the to the distributor ground at the condenser:
The white wire with the red sleeve attached to the low voltage terminal of the armored coil. The instrument responds to ignition discharge and is in series with it. In other words, interruption of the white wires circuit will disable the car.
The red wire from the tach's light socket goes to a headlight switch terminal for illumination.
The other red wire powers the tach and attaches to the upper left, front spade of the firewall fuse box to provide 12V when the ignition is on:
The black wire is for ground. In an unmolested 123 GT, the tach's ground wire attaches to the firewall using the upper left screw which secures the car's Aluminum specification plate to the car. I surmise this may have been a decision taken on the factory floor in absence of sufficiently detailed instructions from Volvo engineering.
This style tachometer is scaled is 0 through 7 (i.e. RPM x 1000). In keeping with the 1968 safety initiative to avoid shiney surfaces in the driver's field of view, the bezel is matte finish, not chrome. The needle is white. The housing is smoother that the "pebble" surface of the earlier versions. It also has 5 wires, but the difference is there is 3 while wires and 2 black ones. The final silk-screened line on this later instrument reads "RVI5413/OO MADE IN U.K.":
In my search for the correct tach, I encountered many other variations in construction, scale and wiring:
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