Caterpillar D20D Electrical & Gauges. If you are not finding what you need for your Caterpillar D20D, please contact us here. You may also want to check out the Lights and Related or Battery Categories in the previous menu. Starters, Alternators, and Generatos are often available new or remanufactured. Amp gauges (Ammeter), Water Temperature Gauges, Oil Gauges, Fuel Gauges, and Tachometers are critical to monitoring performance of your equipment. Sending units and tachometer cables are also available for many Caterpillar.