Alan

I've been wanting to add aftermarket gauges in my K3500. I wanted four gauges, oil pressure, voltmeter, water and trans. temperature. A gauge pod on the A pillar only gives me three and it blocks vision to the end of the plow. Aftermarket "universal" pods are probably going to be anything but universal and I would need two.
I decided to try making one that would hold four gauges, the switch and timer for heated wipers, a few extra switches and my cell phone car mount.
I started by scrounging another instrument panel surround out of a junker. Then I built a "core" out of aerosol foam. After several tries I got a shape that was what I wanted, slightly smaller to accommodate laying fiberglass over the top of it.
Here's the foam core after I separated if from the plastic dash panel. It's partly wrapped with masking tape. The tape is to keep the resin from eating the foam and after it is well coated with car wax it will not stick to the resin after the fiberglass cures.
The grooves are for reinforcing ribs that I felt I wanted in there for a little extra strength. As it turned out, the fiberglass went on thick enough that I could have done without the ribs.

I relieved the core to allow a thick rim around the bottom of the pod. This is wide enough to accept some heavy duty Velcro type tape so that the pod will be removable to allow access to wiring inside it.
Here's the pod after I was done glassing and had pried the core out. The big lump on the end will accommodate the base for the cell phone car it as well as the external speaker. The reinforcing ribs are visible inside the pod

Filler is on and I've been at it with the sander again. Then more filler in places and more sanding to come. Shop floor is starting to look like a light blue desert.

Cutouts are all done and checked for fit. Car kit mounting holes done as well and the switch for the timer on the wiper heat is in. The two dark spots above and below the switch are LEDs. One above will be wired into dash lights so you can find the switch in the dark, the one below is the pilot light for the timer. The blank space between the guages and the switch is reserved for additional switches. When I do the wiring I plan to put in several runs of duplex wire for future use. It's not much fun pulling wire so while everything is opened up I'll run wires enough for future needs.

Done for now! It is now painted and drying overnight. If it's decent weather tomorrow here in God's Garage (the great outdoors) I'll set about installing it. For now I've only got a voltmeter and water temp gauges. Trans. temp is on the way and I'm hoping to find a deal on eBay for the oil pressure gauge.

There's going to be quite a bit of wiring involved, I've got to find a dash light lead and tap into that for the lighting. The LEDs will need resistors so they give a soft glow instead of a flaming beacon effect. I plan to take the gauge power right off the battery, through a relay tirggered by ignition hot. I figure that will give me the most accurate status on the battery instead of somewhere in the wiring harness.

The plan is to leave quite a lot of slack in the wiring so I can just about take the pod right off the dash to work inside it. There's a lot of room inside the shell just for that reason.

I got it installed yesterday, after spending the day before wiring it all up. There's a mess of wire hidden in there. I left slack enough so I can remove a gauge without having to try to work inside the pod. It's hooked down with a super duty Velcro variant, seems secure enough and hopefully it will come off without too much trouble when the last two gauges get here.

At first glance it seems to overwhelm the dash but I can see the end of the hood over it all but the far right corner. When I made part where the cell phone is I carried it straight across the top. Because of the slant of the dash that made the far right corner too high. I've debating modifying it, not sure that I want to go to that much work at this point. I'll probably mount the plow over the weekend and see where the corner of the plow ends up. If it turns out to be hidden I may make some changes.

The first switch on the left is for wiper heat. Next in line is override switch for my auxiliary battery relay. If the main battery comes up dead I can tie in the extra battery during cranking. The last two switches are spares. I ran duplex wire down under the dash and will use them to fire relays when/if I need them.