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MG MGB Technical - dim dash lights
|The dash lights ('69' B) have been dim since I installed the little bulbs I received from Moss. They are getting the required 12v but still dim. Is there a higher wattage bulb that would be brighter?|
Oh perhaps I should try the Little Bulb Car Company !
Any thoughts would be appreciated.
I've been using the halogen bulbs from LBCarCo for several years now. At first I feared that the additional heat would burn or melt something, but that is not a problem at all. One minor precaution I recommend: do not use your dashlight rheostat with these bulbs - just leave it on full all the time. After all, it is more light that you need anyway, and the halogens, while 100% brighter, still don't require any attenuation.
Try 'em, you'll love 'em.
|I found with my '72 GT that bypassing the rheostat altogether made a major difference to the brightness. |
Can you get these halogen bulbs from in the UK ??
|If bypassing the rheostat makes them brighter the rheostat is knackered. I have found that this is the failure mode of the printed circuit types of rheostat, which are the only ones I have seen, as the low resistance elements at the 'bright' (a relative term) end of the movement burn out leaving a higher resistance element in circuit to give a reduced glow.|
Cleaning and repainting the inside of the cases is also said to make them brighter, but a bit of a fiddle.
If there *is* a UK source of the halogen dash lights I'd like to know as well, I've always been interested to discover how they compare for current and heat with the original 2.2W items. If the current is significantly higher, like double or more, than the originals then a full set could damage the rheostat if it isn't already. And excessive heat could affect the operation of the gauges.
|Paul Hunt 2|
|I don't know where LBCarCo gets their bulbs, but it may be worth simply sending Jeff Zorn an e-mail asking him. At the least, you'll get a sense of what shipping would cost.|
I completely agree with Allen - DO get the halogen bulbs. Bad rheostat or not, you'll never be sorry you did.
Halogen bulbs are a nice high-tech way of dealing with the problem of dim instruments. The Old-Timey Mechanic's solution is to paint the inside of the instrument housings a nice gloss white. A much cheaper approach, and not at all prone to needing replacement, ever. Made quite a difference on my car!
I've just seen them in Halfords, 20W (that's twenty). Probably enough to blind you...!
|LBCarCo recommend 5w for the small gauges and 10w for the speedo and tach, unless you have 'green film' gauges in which case 3w throughout, presumably because the extra heat damages the film. It's debateable whether it is the technology of halogen that gives the increased brightness or simply the increased wattage of double and 4 times. And at 10 times the price of tungsten I shan't be replacing all mine, although I'd still like to get one of the smaller ones for testing. 20W would likely melt the gauge! I'm also looking at white LED replacements for both the screw-in and push-in, same physical size, and about the same price as tungsten in the US from SuperBrightLeds, a bit more in the UK from UltraLed. However these would need testing as the rheostat probably wouldn't have the usual effect without an equivalent load or more drastic changes.|
|Paul Hunt 2|
|To cure dim dash lights, I took the advice mentioned by painting the case inner surface gloss white. Made a very noticeable improvement. Now there is no need for halogens in the tach and speedo. There does not seem to be an easy way to remove the case from the smaller gauges, however. Might still need the halogens there.|
|You should just have to turn the bezel willieL.|
A bit of lubricant and some very gently prizing at the tabs on the back edge, where it would not show, did it for me. I also adopted the spray the inside white approach One quick spray with a cheap can of matt ultra white and problem solved. Orrigionaly mine were painted a strange dull blue green colour on the inside. About the worst choice imaginable.
For an instant (about 10% increase) Geoff might reach up behind the dash and shift one of the dimmer wires across to the spare terminal on the other side.
|Taking the lighting current for the headlamps out of the harness and transfering that function/path to relays brightened my dash lamps with NO wiring having been done under the dash. A guess is that when the headlamps share the wiring, they must draw down the current avaiable elsewhere in the harness. What do you say about that, Paul?? Internal resistance of the harness? Or some other factor?|
|Thanks all for your ideas. Remember the '69 did not have a reostat for the dash lights, just an off switch. Perhaps that little switch is corroded enough to cause a current loss. I will pull the wires and bypass the switch and see what that does. Also I put in halagen headlights through a relay so I don't think that is causing a amperage drop. I think I will order up a set of bulbs from LBCC and give them a try.|
Anything less than zero resistance in conenctions in a circuit will cause some volt-drop, and the greater the current the greater the volt-drop, which will result in less voltage available to power the components at the end of the circuit. In 30 year old electrics this can be cumulative through the main lighting switch, dip switch, and various connectors, which makes it difficult to locate and replace one single component to effect a full restoration or brightess. I fitted relays and fuses to the already uprated headlights of a 1980 for someone, and they said the difference was amazing -instead of when he changed the dip the one beam switching off then there being a finite time before the other beam faded up it was instant, as well as being much brighter anyway. He never mentioned that the dash lamps were brighter, but they must have been, perhaps the additional brightness of the headlamps caused his eyes to 'stop down' so he didn't notice it :o) I've just today bought a bright wide-angle LED from Maplins (one of the few places in the UK that still supplies components) so may get the opportunity to experiment with that over the weekend ('er indoors and a leaking house roof permitting).
|Paul Hunt 2|
|Has anyone noticed that on a car which has a 'blown' headlight, the working light seems much brighter than usual?|
This would suggest that the wiring, switch or connectors are restricting the current flow somewhat, when two lamps are connected.
Paul, do you run two seperate fused feed to the relays, or just one? Also, what do you do about the earth return?
|Dave - almost certainly with the small bad connections previously mentioned, as one headlights takes half the current of two, hence half the volt-drop, hence more voltage at the remaining bulb.|
I used a single unfused feed to both (main and dip) relays then individually fused feeds to each of the four filaments. One can put a fuse in the main feed also, but it is only a short run compared to the others and so les chance of shorting to ground. It would also need to be at least 4 times the rating of the individual filament fuses.
The earth return is an interesting point. As I recall it is only 'standard' gauge whereas the 12v feeds to the headlights is thicker than that. On the V8 this is also the return for the twin electric fans which are also high current items. When working to improve these I beefed up the 12v supply to the relay, *and* gave each fan a local earth to the bonnet slam panel under its bracket, in addition to the factory wires. Even when I had the first additional earth installed there was still a noticeable increase in fan speed when I connected the 2nd. Can't say I noticed an improvement in headlight power but by this time the V8 was no longer my daily driver and hence was not doing much night time work. Having said all that, I still think it is the multiple connections (switches as well as connectors) between the wires which are the biggest cause of volt drop, not the wires themselves. There again I have seen evidence of copper corrosion indide the insulation of wires at the front of the car, this will reduce the thickness of the copper conductors, and hence their current carrying capacity.
|Paul Hunt 2|
This thread was discussed between 10/11/2006 and 18/11/2006
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