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Supplemental Information & Instructions for
C34770A Voltage Stabilizer, Negative Ground
13H3554 Voltage Stabilizer, Positive Ground
A Little History
Many British cars produced through the mid 1960s have moving-iron gauges that are fed directly from the battery through a wire that is live when the ignition is switched on. Fuel gauges of this type have two characteristics; the needle jumps off empty as soon as the ignition is switched on, and the needle bounces all over the place when you hit a bump. The readings on these gauges are also affected by the battery voltage, which means they may be erratic or inaccurate as the voltage varies. The new gauges introduced by Smiths in the 60s were based on bimetallic heating elements, and they eliminated these problems. These gauges behave differently; the needles of the fuel or temperature gauge drift up off the lowest reading slowly when the ignition is turned on. The new gauges required the addition of a voltage stabilizer. The original Smiths voltage stabilizer is simply a mechanical voltage regulator that takes battery voltage (13.8 -14V) and reduces it to 10 volts. Inside the stabilizer is a bimetallic strip, an insulated heating wire coil, and contact points. Over time, they fail for a variety of reasons and repairing them is problematic. The Smiths voltage stabilizer came in many configurations- the type and number of terminals depended upon the application, but that all perform the exact same function, providing the gauges a steady 10V.
About the Voltage Stabilizer
The supply of genuine Smiths stabilizers has dwindled to a few part numbers. The ones we have carried in recent years have varied considerably, even when ordered from the same source under the same number. They have had a variety of terminal combinations, which is confusing, and the reliability of some has been suspect.
Reproducing all the original stabilizers would be cost prohibitive, so we set out to reproduce a stabilizer that would meet the needs of all the various applications. We also decided to go to solid state components to improve the quality and simplify the construction, which kept the cost down. The case (1A) is a clone of the housing used on the late Smiths stabilizers. It is grounded to the chassis through the mounting bracket (1B). The instrument terminals are indicated by an “I” (1C) and the power in or battery terminals are indicated by a “B” (1D) just as they always have been. We provide one male spade (3A) and one female spade connector (3B) for both terminals to make it
easy to hook up the original wiring connectors. The solid state components are polarity sensitive and we therefore have a positive ground and a negative ground version of the stabilizer. The polarity of the unit is clearly indicated (2A) and it must be strictly observed.
Before You Replace the Original Stabilizer…
Let’s make sure that is the problem, using the gas gauge to diagnose the problem.
Before you do any testing:
With ½ tank, Gauge Reads High
With ½ tank, Gauge Reads Low
Rule out a problem with the sending unit first.
With ½ tank, Gauge Reads Empty