Sending Unit for Temperature Gauge

They plug into back of instrument cluster, and can usually be found on eBay, or P/N SMP-VRC601 at Summit racing for $33.99. A better option, if I recall correctly, is that there is an article on valiant.org about how to make one out of modern electronic components. The originals are based on 1930's technology and just basically provides a duty cycle of around 33 to 41 percent average on cycle time for a 5 volt output.