Was poking around the pull a- part yesterday and seen something quite strange. In this truck sat a gauge cluster, with the typical gauges, but then it caught my eye. On the right side where normally sits the "brake" light, was a blue-green colored light that said "low fuel economy". I have never seen nor heard of this light, anyone there that can shed some light on this little bulb? Im kinda curious how it works, there was a 3 or so wire pigtail that ran to it and connected into the the dash wiring. And maybe if anyone knows what sort of trucks they came in and why.

 

It's factory. It's connected to a vacuum switch - when vacuum drops below a certain level, the light comes on. I believe it was only offered for one year. It's rare, but there's not a whole lot of novelty to it.

 

I had the same question at one point--here's more info (but not much!) Mikeo0o0o0 got it right in the thread.

https://www.ford-trucks.com/forums/8...nder-hood.html