How to Make Trim Pieces

Since the dawn of the automotive age a century ago, gauges have been required to monitor the condition of an auto engine. Even the simplest internal combustion or steam engine needs a watchdog. Mechanical gauges were the first type used, and they were usually driven by the part they were relegated to check. For instance, early speedometers were driven at the hub of a front wheel on some powered buggies. Water temperature or steam pressure was monitored at the radiator with a Manometer (a water thermometer) or a direct-sight steam gauge at the boiler.

Idiot Lights
As automotive electrical technology progressed, so did the gauges used by the manufacturers. For the less expensive models, lights activated by sensors (called idiot lights) would illuminate when the oil pressure was too low or coolant temperature too high. They also had a habit of lighting up too late! These idiot lights carried on through the mid-Sixties until the advent of printed-circuit technology. This was the first real step forward in gauge accuracy and simplification. Here we'll look at two gauge clusters that are only five years apart in time but light years apart in technology.


The gauge cluster on the left is from a 1965 GM performance car and the cluster on the right is from a 1970 vehicle of the same type. Both utilize idiot lights for oil, temp and amps, but the difference between the two is dramatic. Because wires attached to each gauge operate the earlier gauge pod, three pods are required to do the work of two in the newer example. Using a printed circuit, fuel, oil, amp and temperature gauges are all in one pod next to the speedo. Obviously this was less expensive to manufacture and drastically reduced the size of the pod required.


Here is the rear view of the same pods in the same positions. The top cluster from '65 had individual light bulbs that pressure-fit into the holes in the back of the case. That's the reason for all those holes. Two bulbs, which were grounded on the metal case, illuminated each gauge. The instrument cluster wiring was a maze of bulb wires and sending-unit wires for the idiot lights plus the screw-in speedo cable. The 1970 cluster was fitted with a printed circuit with twist-in light bulbs that eliminated the need for all that wiring and made changing bulbs a lot easier.


The rectangular slot at the top is for one major gauge-operating plug. The signals emanating from engine compartment sending units travel through this plug and then to the printed circuit paths and on to the individual gauges or idiot lights. So all the wiring used in the early cluster is gone and a single wire does the job. The '70 speedometer cable in no longer screwed into the receptacle at the right but held in place by a push-in spring clamp. You can reach under the dash, push in the spring clamp with one finger and pull out the cable. These innovations were not for the consumer's convenience but rather for the assembly line worker or dealer technician to simplify the procedure.