MGB: Halogen Dash Lamps from lbcarco.com - WOW

OK, so I just swapped out my dash lights with halogens from Little British Car Co.. 5W bulbs in the three small gauges, 10W in the two large ones.

Before I made the change, I was in the usual situation where the dimmer was a joke. When I had it all the way up, it was just barely enough, and I like my dash lights pretty dim! Now I actually am dimming them down. Really!

Now I just have to figure out why the ground on my speedometer is not completing. I can reach up and touch the gauge back and it will light up. I will check the ground wire itself, but I think it is the same one that is working for the middle gauge, if not all five gauges.

Part of this is likely the fact that I have only one of the braces installed on this gauge to hold it in place. BUT, that is true for the tach, too, and it was how I got the car, and the lights were working then, until they blew. So, where does the ground go on the tach and the speedo? On the rest, I have them connected on the post that holds the gauge in place, and I think that the tach and speedo are the same.

On my 71 the ground wire is held in place on the tach and sepeedo by the knurled nut that holds the bracket which secures the instruments.

Yup, the threaded post. Should be a black wire with ring terminals.

Got any pictures of them installed?

You could always run an additional ground to the guage.
You can never have too many grounds!

I agree, made the replacement a while ago and what a difference. My aged eyes can actually see the instruments at night now. I replace the brake lights too. That made a great improvement also.

I am curious about the load on the dash dimmer. In the past there have been cases of the dimmer overheating when not on full. Do the halogens draw less current thus avoiding this problem? I painted the interior of the gauges with high gloss white which made a difference but they are still pretty dim.

I have LED tail and turn lights which are very bright, has anyone compared the halogen to LED?

Norm

A watt in DC voltage is volts X amperes. A watt is a watt no matter what is using the power. Therefore using the nominal 12 volts, there are two 10 watt bulbs and three 5 watt bulbs which is 35 watts total going through the dimmer which is about 3 amps (35/12). 35 watts is about what a low beam in the head light uses, and the dimmer converts the electrical power into heat when you use it. My guess is that the dimmer would be undersized for this current load.

Just a quick lesson on Direct Current electric power. As stated above electrical power is: voltage times current=watts. Bulbs are rated on how much power they use, watts. This is an indication of how much light they put out but when comparing two types of light bulbs, fluorescent versus incandescent, the fluorescent bulb will convert about 22% of the input watts into light with the remaining 78% is turned into heat. Incandescent bulb only gets about 10% of the input watts into light with the remaining 90% is turned into heat, you know, the bulb get hot. Halogen is somewhere in between Fluorescent and Incandescent bulbs and LEDs are about 40% efficient.

AC voltage is a different animal with motors because of inductance, phase angle etc.

I would guess that the halogen bulbs are rated at a higher voltage than the stock bulbs. Thus, more current and more heat.

A watt is a watt. But - halogen bulbs provide more light at the same wattage as normal incandescents. The theory is that the filament in a halogen bulb runs at a higher temperature than conventional filaments. In fact, it runs at a temperature that should cause it to burn out. However, the ions that boil off are contained near the filament by the halogen gas and redeposited.

Also, don't confuse higher temperature with more heat. A campfire has way more heat than a dash lamp, but runs at a lower temperature.

The theory is all great - but I've really got to get some of these bulbs myself.

They're pricey, but well worth it. I've been using them for almost 2 years now, and love 'em.

mgacarnut Wrote:

Norm73B Wrote:

Just point out another thing, the 5 halogen bulbs use 35 watts which is about the same amount of power as the low beam on a head light. That is a lot of light, imagine a head light aimed at your dash. That said it also points out how much light is "wasted" inside the instrument housings.

Aah - if the wattage is higher than stock, then it definitely increases the wattage dissipated by the dimmer. Interestingly, the dimmer will get hottest when set to half power - probably right about where you need to run it for proper operation.

ingoldsb Wrote: