It was used on 140 series Volvo's when they went from the fragile capillary temp gauge and twitchy instant read gas gauge of the 122/544 series to the steady, smooth, and more reliable gauges of the 140 series. These gauges operate at a lower voltage (8??) and the voltage stabilizer drops the voltage down to the lower level needed. If the gauges run at full 12 volts they will all peg out and burn up in a relatively short time.

To complicate things they didn't want the gauges to slowly creep up to their correct readings, so the voltage stabilizer has a bypass which sends 12 volts to the gauges for about 1 second before a little heater inside kicks the bypass open. Only after it has been switched off for a while will the bypass cool off and close again. This brief shot of 12 volts is what makes the gauges jump up quickly when the key is turned on, when normally they react rther slowly. This bypass can stick on if the little tiny heater wires wrapping the bimettalic arm break, frying the gauges. Its a little relay looking gadget that hooks to the back of the instrument cluster on a 140 series - I'm not sure where it hides out on an 1800 - I've never seen it under my 1800E's dash - but then again I've not spent a lot of time looking under there either... :)