I guess you could classify this as a "two'fer" project as I am accomplishing two objectives. First, I needed a place for my TPMS monitor, and second, the overhead courtesy light was wimpy to say the least. So my overall goal is to find a place for the monitor and replace the light with something better. It's amazing the stuff we take camping with us these days, but anything that helps get you safely to the campground is a good thing.
The logical place - at least as I saw it, was to make a plate that would become an overhead console. I found some 1/2" Corian in the color Chamois, so as I have worked with Corian before (it works with standard woodworking tools), I thought I could make one with that material.
If you have never worked with Corian before, you can still make a nice console out of wood. I'd suggest a wood like Mahogany (which is stable). The trick though is how to finish such wood. I would recommend 5 to 10 coats of sanding sealer, followed by some glossy enamel. If you applied sufficient sanding sealer, there will be no woodgrain showing in the finish.
Conceptual Console Base.
(Note: the console drawing is just a guide. I suggest creating a cardboard template for the console size and test fit prior to cutting anything).
Since I discovered 16AWG wiring is already run to the existing light, it should be sufficient for my project. One thing you have to realize with DC wiring - discovered by none other than Nikoli Tesla - is that the longer the wire, the more voltage drop you will realize.
For example, you can safely use 22AWG wire for 12VDC at 3Amps. However, if the wire is rather long (more than 10ft), then series resistance in the wire will result in lower voltage at the distant end. Even though 22AWG can safely handle 3Amps, you may find you only have 8VDC at the distant end, which is not acceptable.
Typically the only remedy is to increase wire size. If you go to say 18AWG, you will maintain close to 12VDC at the distant end. So in this situation, the larger wire diameter is to ensure enough voltage is present at the distant end, not the current.
So by re-wiring the light circuit, I have to ensure I don't put too much of a load on the circuit that while safe current wise, might reduce the voltage to an unacceptable low level. However, when applying the standard voltage drop formula, I find that for 16AWG that I can pull 3A with only a 0.12V drop, which is only a 1% loss.
Even for critical electronic circuits, the rule of thumb is an acceptable 3% voltage drop (0.36V), which would allow over 6A of current draw. So, I think I am not going to have an issue. The light fixture I am replacing requires 2A by use of 1004 bulbs, but I am going to swap those out with LED bulbs that will require around 200mA total. And the TPMS monitor requires less than 2A to operate, so I am really in good shape with the wiring (meaning I don't have to run new wires).
However, the circuit is a bit goofy as it is for the overhead light. Anytime you open a door, the circuit is powered for about 5~10 minutes, then automatically shuts off. And when you are running the engine, there is a constant source of power to the circuit. This is OK, as for the dome light, this is normal behavior... and for the TPMS monitor, it has it's own internal Lithium-ion battery, so the circuit actually only powers a battery charger.
Construction of the console was pretty standard stuff, using standard woodworking equipment. In the construction I used a bandsaw to cut the piece to shape, a drill press for the holes, and several different sanders (bench and portable) to obtain the final shape. The only unusual item was my "poor man's" milling machine (a drill press, milling bit, and x-y slide table) to cut a slot in the underside for the wire run (which was ultimately secured with a bit of hot-melt glue).
You can get a very nice glossy finish with Corian and similar solid surface materials by using "Micro mesh" sanding pads. You can buy a kit of these pads having grits from 1,500 to 12,000. However, like any other sanding project - start out with 100 grit or so to get rid of the machining marks on the Corian before going to the sanding pads.
Other items I used were Forstner bits to cut a relief in the underside of the Corian for a couple of T-Nuts for the new light fixture. That way, I would not have any difficulty in attaching the fixture. The TPMS monitor wire uses an in-line 2A fuse, so to make that fuse easily accessable (so I would not have to remove the console plate), I placed the fuse in the void of where the light fixture would go.
Mounting the console plate to the cab was serious business. If not careful, you would potentially drill a hole through the roof of the cab, and that would be bad news. Here is where you should not use any power screwdriver or anything like that. I attached the console plate with four #8 sheet metal screws. The proper pilot hole drill for these screws is 1/8" dia, and so I carefully drilled the four holes... luckly without puncturing the cab roof.
I was pretty confident in drilling the front pair of holes without puncture, as I removed the trim panel and could peel back the upholstery in the ceiling and see that there was a metal channel running under the cab's roof. So I simply drilled 2 holes into that channel to mount the front.
The rear presented an additional challenge. I had hoped to drill into the plywood base of the front over-cab berth, but after a bit of poking and prodding around, I found that there was an aluminum L channel under the plywood, so I ended up drilling through the upholstery and Styrofoam block into the channel.
I didn't have to worry about using any standoffs through the Styrofoam block as the surface area was such that the console plate doesn't crush the Styrofoam. Also, the more careful you are here in this area the better. You don't want to snap off a screw which you cannot retrieve, so leave the power screwdriver on your tool bench and use a hand screwdriver.
Wiring the light fixture. The TPMS fuse is easily accessable
under the light fixture should I ever have to replace it.
The TPMS monitor is high enough so that it does not interefere with the mirror, however the point is moot. The mirror gives you a good view of the master bedroom, and that is about it. So there are really no issues concerning the lack of clearance around the "bedroom-view" mirror.
Plenty of clearance above the mirror.
After using the TPMS monitoring system in the console for some period of time, it became apparent that the display was hard to see from the driver's position due to the angle - or lack thereof - of the display. What is needed is for the TPMS monitor to be angled towards the driver. The console was modified for this purpose by alloing the monitor's azmiuth to be adjusted.
Admittantly, a bit of machining skill was required to make the modification, especially to fabricate the standoff, which required super gluing 3 pieces of 1/2" thick Corian together then cutting it to size. Be careful here... I used a table saw to make all of the cuts, using an appropriate jig. Your fingers can come awfully close to the saw when machining such small components, so keep them away from the saw blade by using home made jigs and fixtures.
I would consider such work an advanced skill level. DO NOT ATTEMPT if you do not have the skill to do such work safely.
The wheel itself was made of 1/2" thick Corian "Nocturne" (black) which can be hard to find. Check eBay for small quantity of such material. In fact, if I could have found enough Nocturne at the time I made the original console, I would have used it. Unfortunately, I could not find any at the time.
The wheel was rough cut by using a hole saw, then finished and polished on a lathe. When adjusted properly, the lock nut (with nylon insert) provides enough friction to allow the TPMS display unit's azmuith to be easily adjusted by the driver, yet provdes enough holding power so it does not move on it's own.
I am providing conceptual drawings rather than detail drawings as anyone attempting such a project should have the skill set to take the concept and fabricate the items that are needed... better yet, you may have a better solution.
The backside of the display unit shows the changes I made. You can see how the wheel in the photo corresponds to the one in the drawing. I ended up having to hot-melt a bit of glue to the display unit as it has become a very sloppy fit. The other thing I had to do is replace the power cable as I made the original one too short to accomidate the azmuith swing of the display.
Now I can swing the display unit left or right at ease. One issue though is the sun visor will hit the edge of the display if it is rotated too far towards the driver and you attempt to lower the visor. About 10 deg of rotation is max before this occurs. This is not a huge issue as you simply can return the display back towards the center to drop the sun visor.