I also followed this same path of putting an LED in a dash screw as a warning light.
In my case I wanted to have an indication of my oil temperature. Having just installed a new dash it was too late to add a hole for an oil temperature gauge. In any event, an idiot light that indicated cold, warm, and hot would do the trick as well.
I installed a programmable Autometer Oil temperature gauge in the glove compartment. Then used that to drive a tri -color LED (Red-Green-Blue) as follows:
Blue: Cold, wait before romping on the car
Green: Warm, good to go
Red: Hot, reaching breakdown temps. (highly unlikely).
I drilled the dash screw as much as made sense given that I had 4 leads (R,G,B, cathode) to feed through. To make this work I lengthened the LED leads with the same small gauge lead wire before attaching the larger gauge (22) wire for hookup to resistors and the gauge/relay wiring). Used small shrink wrap to allow all four leads to fit inside the screw as per the picture. Relays were used to create the logic paths of when each color was triggered.
The indicator works great (don't know about Red - don't ever expect to reach that regime). But, the light starts out blue and then changes to green as per set limits.
I added additional resistance to the green lead so that in normal driving the light would be unobtrusive. Blue however is bright with the selected resistor, but it is only on until warm.
A very neat solution not involving drilling any holes in my pristine dash. I had been all set to add a dash light similar to the parking/brakes/hazard lights requiring the drilling of a 1/2 inch hole, somewhere. But thanks to the fortuitous timing of another member asking about the LED dash lights this alternative solution was perfect.
Only thing now is that it appears that the oil temp, as measured at the sump generally shows a pretty cool 140-145 F (62 C). I believe the oil cooler sandwich is set for 165 F. Also, pretty cool. Meanwhile the water temp is typically around 175 F (80 c).
I am initially (haven't put many miles on the car) concluding that :
1. The sump temperature at the plug sensor is probably 20 degrees F cooler than at the filter head.
2. Also that the water temp and the oil temp, after steady state is reached, are consistent if one assumes that the sump temp takeoff is 20-25 deg cooler than measured at the oil pump.
2. But, concerned that these indicated cool temperatures, if valid, are not necessarily good for the engine?
Ironic, because until the rebuild of my car I was always plagued with running hot. Now, I have to idle in traffic, without moving, in warm weather for 10 minutes before either the water or oil temperature approaches 200 F (93 C). More than ample cooling capacity even with a high output engine! Maybe in full race mode (not my case) the cooling capacity would make more sense. On the other hand today it is 107 deg F (42 C) and I would probably be thankful. But too hot today to even venture out and drive a drophead anyway !
- Lengthened LED leads and shrink wrapped
- Fed through the dash screw
- Gauge in glove box
- Green indicator (low light level)