Transistor in rally gauge ?
All vehicles originally had 6 volt electrical systems. Rather than redesign/engineer the instruments when 12 volt systems came along they added a mechanical voltage limiter to power the same gauges. The limiter was housed in a rectangular metal can attached to the back of the inst' panel with 3 heavy male spades ( sort of like a household wall outlet plug ). Because the mechanical limiter worked like a set of points creating a pulse voltage, it created a electrical spike. Thus a pop noise would occur in the radio speaker. So a noise supression cap' was also added. It typically had a single screw to mount and ground it to the back of the inst' panel along with a short wire and connector terminal.
So whats different about the A-body rallye panel? The standard plug type in limiter was built to supply two thermal gauges, either two of 20 ohm gauge or one 20 ohm and one 13 ohm. The rallye panel has three of 20 ohm gauges. These have heavier needles that pivot on a post through them in 2 places. That standard limiter wouldn't work as well here. The gauges needles would be slower plus a full tank of gas versus a empty tank could make the other 2 gauges read a little different. All these so called gauges are really just simple range indicators so customer complaints was likely their only concern.
Solution... They put a special duty limiter inside this fuel gauge. The wrong limiter could not be substituted in the field.
This wasn't a new practice. They had placed limiters inside other gauges several years earlier. Imperial for one had its limiter inside the temp' gauge.
The E-body rally panel had the can type limiter but it was remotely located instead of plugged into the panel or inside a gauge. They all had some limiter somewhere.
So anyway... fast forward to modern technology and you get "the fix" suggested... Replace the mechanical limiter with solid state regulator no matter where the limiter is/was located. Result is a steady flow of reduced voltage with no spike/pop noise. No suppression cap' req'd.
