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MG MGB Technical - Dashboard lights. Again


Hi Guys, Further to my earlier thread, would anyone know the aperture size in the back of the instruments that carries the bulb holders? as that seems govern size of the bulb you can use. Are all the holes the same size? I have tried laying on my back to peer up into the dark corners of the beast but I am afraid my size prevents me from getting a good view. What Im hoping is that someone out there has some non fitted, or waiting to be fitted instruments that they would kindly measure in mm for me. I have tried pressing Blutak on to the hole but that doesn't work well as I need an accurate measurement Regards Peter As the image didn't load,trying again.



PM

Don't your bulbs simply pull out? Mine do, so just measure the diameter of the push-in bulb holder. The holder determines the type of bulb that can be used, and yes all gauges and holders are the same on any one car (or were originally, a PO may have swapped a gauge or two).
PaulH Solihull

Yes, sorry Paul,
I must have been miles away. Clutching at straws I suppose, just can't seem to solve this problem of dingy instrument lights. I suppose that the answer is either go down the LED strip route with the 500 ohmn 3w potentiometer, which means taking all the instruments out, taking them apart and then rebuilding them or put up with the fireflies that live in my dashboard. I suppose I just can't get my head around the fact that you just can't get higher wattage bulbs in the MES size. My last chance might be BA9s which do come in that size with higher wattage, but would have to change all the holders.I wont my breath. Cheers Peter
PM

Shorting out the rheostat got mine up to point where I can happily live with them. I have read about painting inside the instrument white in posts on here.
Stan Best

Thanks Stan,
I think that if one is going to paint the inside of the cans white you might as well do the LED bit as well. I think the shorting out of the Rheostat might be worth a try first. How did you do it? Any diagram or picture would be a great help. Peter
PM

There should be two pairs of terminals on the back of the rheostat. Just move one wire so that it is on the same pair of terminals as the other.

Here's a photo I lifted from fleabay...

Dave O'Neill 2

Years and markets do vary, some only have one wire on each pair of spades so it is easy to move one over to the unused spade of the other pair (doesn't matter which). Others use both spades on one side, so requiring a bit more ingenuity to bypass. If bypassing the rheostat *does* increase the brightness, even when on its brightest setting, then it is faulty. All the rheostats on cars I have had have been like that, they have all been the printed circuit type, and they can burn out such that turning the rheostat does vary brightness, but won't go up to full brightness. Replacements are very expensive for all the use they are, but I hate having things that don't work.
PaulH Solihull

Hi PM,

The lighting hole is 15mm diam.

Herb
Herb Adler

I seem to remember having a spare kicking about - thought that only had a sort of coiled up spring giving the resitance as the knob is rotated - not sure about circuit boards ?

Available if anybody wants it - Spridget owner only these days !

R.
richard boobier

To get back to your first question. I have a '71 Australian rdstr which has toggle switches. I think the dashboad is the same as a UK mk1 model. The dash light holders are 12mm dia for the fuel,& oilpress/temp gauges & the hi beam & ign warn lights. The tacho & speedo gauges & the turn indicator lights use 15mm. Barrie E
B Egerton

The one posted above is a rheostat, a coil of resistance wire with a slider rubbing on it, these generally have ceramic bases as that one appears to have. My burnt-out printed circuit type attached, damaged section at the bottom.

I only have one car at a time available (for the next two weeks anyway) but my 75 V8 (80mm speedo and tach) are about 0.482" i.e. about 12mm for all for gauges. I'd say my 73 roadster is the same, which has the 100mm speedo and tach

PaulH Solihull

yea, the rheostat is the bottleneck. I pulled mine, soldered, capped, and insulated all the lighting wires together, and placed a new choke cable in the old rheostat hole when I installed the Moss SuperCharger . Still didn't like the night light and pulled all the gauges out and apart, painted the inside housing can flat white ( per Bigface, but I've wondered about the mirror-like adhesive reflective foil as a better option) including back of the front face for the oil/water/and fuel, q-tip polished the green color hub inside and out, treated the front face of all gauges with dri-wash after "Marks Alot"-ing the scratches, discolor, and white specs which seemed to be around a bunch on the faces, coated every needle with "very white" correction fluid to turn them back from yellow to bright white, and tipped the needles red to show I had been there, replaced all the glass and polished the speedo plexi back to clear from yellow, then finished the work using new chrome bezels with new rubber glazing seals all round.
Still didn't like the night show, although the gauges looked great in their fresh dress.
So, I went with superbright LED strips on the 100 mm speedo/tach inside, and tried 120* dispersal super bright green LED on the 4 smaller gauges ( see upload pix below). Night lighting was greatly improved, although the small gauges were lit uneven due to the narrow LED emission band.... so I rotated the rig until I got the most even perimeter lighting. All told a huge improvement since byepassing the rheostat.
Rumor is the very expensive, short lived halogen instrument bulbs are super and light up the cockpit and a desert night, but melt the green color hub. Anyone have personal experience with these buggers, and who is selling them now please? Below, I include a pix of the LED as well on upload.VEM
vem myers

Help, I've got 2 great jpeg to show the gauge and int LED above post, but am told the "file is too big". I'm dumber than a bag of nails on compression and the like, so if one of you wonderful guys will help, I'll try to upload after correcting those "big files". What do I do? And why couldn't we just embed a photo into our thread blog here? Vem
vem myers

ok, here's a pix

vem myers

and the LED, both strip for the 100 mm gauge and the bright green single for the 52mm little guys

vem myers

Boy they are big! You should resize them down to 1200 pixels wide or so.

It was the 7v Radio Shack bulbs that were very bright but short-lived - like a firework - not surprising since they were being worked at double the rated voltage. 12v halogen are also bright but long-lived, however they get very hot - compared to 30C for 2.2w and 55C for 4w conventional a 6w halogen ran at 90C, even though the current was pro-rata. LBCarco recommended 10w for the large instruments and 5w for the small, but only 3w for the late 'green' instruments as the higher wattages do indeed melt them. At the time of investigating they were also 10 times the price of standard bulbs. They may have had too many problems with them as they only seem to list standard bulbs now.
PaulH Solihull

Well, I think I'll keep going on the LED then. Seems to me some bright inventive guy could provide an umbrella like dispersal crown around the LED. Paul to your knowledge, what's the best dispersal currently that the LEDs offer. Is anyone selling the 10x cost halogen nowdays? Closing thot: couldn't the 7v Radio Shack bulb be resistored down? Couldn't one use a 5w halogen in the large gauge and a melt proof colored hub from Summit or VDO, replacing the original plastic hub, with a 3w halogen then for the 52mm gauge? Just spitballing. VEM
vem myers

If the Radio Shack is resistored down it will be dimmer, who much dimmer, or brighter than the original, while gaining longevity would take quite some experimentation.

Doesn't seem worth all that trouble when the LED strips seem to do the job.
PaulH Solihull

This thread was discussed between 16/09/2011 and 27/09/2011

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