I needed to be able to switch the F-250’s dash fuel gauge between the normal tank and the aux tank. I needed a 2nd switch to turn the aux tank’s fuel pump on. The danger was that the aux tank pump would go on, or be left on, unintentionally. If the aux tank went dry the expensive OEM pump would overheat and die. If the normal tank got over-filled the high pressure would blow out something in the tank and vent plumbing that wasn’t meant for the pressure and many gallons of diesel would spill.
The first iteration of switches to control the F-250’s aux tank pump were switches that I had laying around. I’d ordered better ones, but I’d gotten impatient and pulled some matching switches out of the “switches and LEDs” drawer. I used a standard household switchplate as a box cover…Not ideal, but that too would be improved upon.
I did a lot of hunting around for switches. I wanted the switches to look identical and I wanted the pump switch to be illuminated red when turned on. Turning something on just requires a standard single pole, single throw (SPST) illuminated switch, something you can get anywhere. “Single pole” means 1 circuit. “Single throw” means 2 positions…on and off. But the fuel gauge switch was harder. For that I need double throw (SPDT) which means the switch has 2 “hot” positions, you can make one circuit hot or you can make the other circuit hot. That would allow me to switch the dash fuel gauge between the normal tanks sensor and the aux tank sensor.
Altho there’s lots of illuminated single throw switches, because if you’re switching power it’s easy to siphon some of that to run an LED, there’s not too many illuminated double throw switches. The reason for this is that double-throw switches are not just turning power on, they’re switching between 2 things…and maybe neither of which has 12v. For, example, if you using the switch to deliver a ground to two different circuits, you don’t have squat for power. So what was needed was a switch that had separate power contacts for the illumination, and that made it a rare bird.
It took a while but finally I found some kick-butt switches at Mouser. They would illum amber/green in one position and red in the other position. They sounded awesome, but I worried that when they showed up I’d find that I misunderstood their spec sheets.
When the switches arrived I did some testing on them to make sure I understood what all the connections were. They turned out better than I’d hoped. They were more expensive than radio shack and autoparts store switches but the quality was so much higher that they made me realize that most of my switches in the “switch and LED drawer” were crap.
The next problem was to find a way to protect the switches from getting bumped. Both gear or the kids could easily bump the switches. My initial plan had been to use rocker switches on the dash in some out of the way position. Rocker switches don’t stick out much so they’re bump resistant. But the more I looked at places on the dash I could use and the kinds of rocker switches available, the less I like the rocker switch idea.
So if I was going to use toggle switches and an aux box, the switches needed some kind of cover to keep them from being bumped. The cover needed to be clear so if the switches were in the red position that would be immediately obvious. Finding a good cover solution took another several days, but I eventuallly I found the perfect solution at an aviation supply house. They sold clear toggle switch covers that you can fasten over any normal toggle switch. Awesome.
Even cooler, when the clear toggle switch cover is closed, it automatically flips the switch. So the result of any bump is the aux fuel pump being turned off. It’s spring loaded so if it gets bumped, it flips down hard enough to pop the switch.
Finally, I ditched the household switch box faceplate for a smaller faceplate.
Aux tank switches Mod 0. Cheap non-illum switches, free to be bumped, and big off-white face plate.
Aux tank switches Mod 1. New face plate is smaller and looks better.
Aux tank switches Mod 1. Close up showing switch covers. Note that fuel pump is now on and therefore red. Should cover be closed it turns switch off.
Switch covers http://www.skycraftsurplus.com/safetycoverfortoggleswitch-assortedcolors.aspx