I used the original Ford pickup bed cargo light indicator light that was used in the 289 slabsides . It comes apart to allow me to install three tiny "grain of wheat" bulbs (available from hobby shops.) Two are wired in parallel (for redundancy) to an
oil pressure "idiot light" sensor and one is wired as a charge light. My theory as to why Shelby wanted such a big light in easy view is that in a race if you lost a fan belt it would alert the driver. In contrast he picked the tiniest light in Ford's parts box for the high beam indicator as it wouldn't distract the driver in a race. That light was used in 1940 Ford pickups!