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MG MGB Technical - Dash Bulbs

Hi Folks

Saw these on e-bay. Read the archives and did not see anything on these.

http://cgi.ebay.com/ebaymotors/8-Watt-Dash-Lights-MG-MGB-Triumph-Austin-Healey_W0QQcmdZViewItemQQcategoryZ6763QQihZ017QQitemZ270083676340QQrdZ1

Says 8 watt. What effect would that have on a 67 B with a Lucas alternator?
BEC Cunha

None.

Now if you added these at the same you added a BF CD player with 150-watt amp you may have issues, but these won't make any difference at all.

And ignore all those folks who're gonna come in here and tell you that new bulbs aren't the answer, that cleaning contacts or bypassing the rheostat is the answer. New bulbs do help. The originals were 2 watts brand new. Put 2w bulbs in any modern car, and what do you get? Darkness. Same goes for a B.

I've got halogens in mine, but these are okay.

R.
Rick Stevens

If you fit 8W instead of 2W you will need to bypass the rheostat as well.

Next time you have the clocks out, make sure they are clean and white inside, (or pale blue) as they were supposed to work by reflecting the light all around the rim onto the face.
Martin Layton

Bear in mind that LBCarCo sells halogens at 5w for small gauges and 10w for large, but they recommend only 3w for what they describe as 'green film' gauges. I suspect this is because the much greater temperature of halogens damages the gauges if the higher wattages are installed. As well as being ten times the price of conventional tungsten they do a generate a lot more heat - like 30C for a tungsten and 90C for halogen. However the current is much the same for the same wattage. I used to think that, as burnt out rheostats are very common, they must be marginal with the standard bulbs and so using higher wattage bulbs of either type would be sure to burn them out. But whereas early cars only had 4 lamps late model cars had about 10 or 11 with the extra gauges and the switches, so 'normal' current can't be the issue. I tend to think now that at some time one of the instrument lighting wires shorted out which would blow the rheostat in short-order as they aren't fused. Current *will* be an issue with higher wattage bulbs if you park with the lights on and don't dim the instruments.

All the rheostats I have seen have been of the printed circuit type and their failure mode is not total but just dimmer, still being variable. If bypassing the rheostat brightens your lights the rheostat is faulty, it will make no difference with a good rheostat. Cleaning the bulbs, or fitting new ones which don't have that black film inside, cleaning the glass, repainting the inside of the cans, all help.

led bulbs are noticeably brighter (in the large gauges anyway, see http://www.mgb-stuff.org.uk/wn_electricsframe.htm and click on 'Lighting' and 'Instrument Lighting' and scroll down), much cheaper, less heat and less current than halogens, but render the rheostat superfluous.

But at the end of the day (i.e. at night) the beauty of analogue instruments is that you don't have to 'read' them anyway, just see the angle of the pointer. If you don't know what the angles mean you should drive it more!
Paul Hunt 2

This thread was discussed on 27/01/2007

MG MGB Technical index

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