I have installed water temp and boost gauges in my R56. The gauges work fine but I am having a problem with the lighting. One bulb in one gauge works fine, but the bulb in the other gauge is burning too hot and has killed two bulbs already. The good unit allows you to touch the bulb. The bad unit is so hot you can't even touch it. I'll describe the current wiring and maybe someone can help me troubleshoot the cause:

I have wired the illumination to the DSC illumination wire in the center console to allow dimming. this is the same wiring as suggested by ALTA for their gauges. I ran that up to the gauge illumination units with one wire. At the gauges I split the single power wire into two wires, with one running to each illumination unit/12v bulb power wire. I run the ground wire from each unit to one single wire attached to ground.

So, I have one power wire that splits between the two bulbs, and two ground wires that combine to a single ground wire.

Do I need separate grounds? Separate power lines? Why is one bulb running hot and the other is fine if they use the same power and same ground?

Thanks!

 

The wiring sounds fine. No need to split the grounds or power. It seems that more current is running to the brighter bulb. I would check the resistance of each bulb and perhaps add a series resistor to the bulb that is too bright. This should balance the system. Good luck. -- Pete

 

Thanks! Any guidance on what size resistor for a 12-volt line using 18-gauge wire to get the bulb to dim a bit?

 

If you want to match the intensity of the other gauge: Measure the resistance/impedance of both and subtract to get the difference. This will equal the size of the resistor you need. A 1/4 Watt version should be more than adequate. -- Good luck...

 

I think I figured it out. I was using Sylvania amber bulbs to match the tach lighting and was using 12volt, but too high a wattage. ithink that was exagerating any minor discrepancy. The volatge across each socket was the same, so it had to be the bulbs. I am back to the bulbs that came with the gauges with a ton of orange marker on them. We'll see after the next long evening drive.

Thanks for the input, guys!

 

I saw your gauges. They look great. I would love to do it to mine. Can you provide me with more details of the install?

 

I followed the istall instructions, generally, from those who posted on here about their ALTA gauge installs. The wiring is a little different for my gauges, but not much. I used the same source of switched and lighting power under the center console (lighter and DSC). I had to craft my own ground for the water temp sensor because I wasn't screwing it into the engine block or manifold.