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MG MGA - Bit missing - electrical
| I have a MGB tachometer in the dash. At the bottom, there is an opening for a lamp, but it seems to need a bulb holder, or receptacle for a bulb holder, just like the bottom light on the speedo. Would anyone happen to have one of these adapters? (for want of a better name) Its a small tubular fitting, larger where the bulb goes and smaller where it fits in the instrument case. I can't see a listing for one anywhere. |
| Art Pearse |
| Pretty sure I have a couple, I will have a look over the weekend |
| dominic clancy |
| Thanks Dominic, send me an email |
| Art Pearse |
| Art Is this what you need? Dominic  |
| dominic clancy |
| Hm, not sure. See pic of the back of my dash. On the speedo (black) there is the tube where the ign light goes. This is what I thought is missing from the tach, something to collimate the light so it is aimed at the jewel in front. The large end is 5/8" ID and the ign lamp fits. The hi beam lamp holder is the same size as the ign, but the hole in the back of the tach is only 0.59". This is actually larger than the hole in the back of the speedo where the adapter fits, so it looks like its not the same set up on the MGB tach as the MGA speedo. Your bit might be right if it holds the bulb and plugs into the 0.59" hole. Did it come from an MGB?  |
| Art Pearse |
| MGB tachos have a plastic tube that fits into that hole and locates over the lens on the dial face. I'll see if I can find one to photograph for you. |
| Chris at Octarine Services |
| Aha! The bit you are missing is a plastic funnel like thing. It has a tube that projects to the back of the telltale jewel in the dial face. Does the light fitting to this have a clawed bulb holder? The reason I ask is that I think there are two versions of the plastic thing. One takes the fitting I have photographed, the other takes the standard clawed fitting. I will have to look in a different box, but think I have one to take the clawed fitting somewhere. Otherwise you need an original gauge casing. With the originals from the MGA, there is a rubber tube that goes from the funnel up to the crystal. |
| dominic clancy |
| Art, Barney's site shows what you are looking for. There are, if I recall, three different bulb holders for the different tachs. The MGB ones are different to the MGA one (clawed type). Peter. |
| P. Tilbury |
| Art Just had a look at my MGB rev counter. If you look at my picture you will see that a long plastic sleeve inserts in the hole. The standard MGA bulb and connector can be used by using the grips on the holder to clamp on to the plastic holder, making contact with the two metal retaining contacts on the sleeve to provide the earth. I need to clean those contacts while I have it out! Steve  |
| Steve Gyles |
| Steve, I may have to resort to fabricating one from your picture! |
| Art Pearse |
| Steve, is that bulb holder(the bit with the wire and bulb) MGB or MGA? |
| Art Pearse |
| Art I assumed it was MGA, but you have me thinking now. It is possible I replaced it when I put the MGB instrument in - I cannot remember, it was 13 years ago! Perhaps someone else can advise us. Steve |
| Steve Gyles |
| Art I had an inspirational moment and went to inspect the loom! It is the original that came with the loom and is the same that plugs into the Jaegar speedo unit. Instead of the claws fitting inside the 'tube' as on the speedo, I have the claws clamping around the outside of the MGB instrument plastic tube. Not perhaps as it is intended but works okay. Looking at the wiring diagram it does not earth through contact with the two metal retaining pins on the plastic tube. There are two wires out the back of the bulb holder, part of a continuous circuit, earthing elsewhere. And as a practical test I pulled the holder off the plastic tube and the light remained on with the ignition switched on. I am surprised no one picked me up on that one from my earlier post! Steve |
| Steve Gyles |
| The tacho one is not earthed since the ignition light wiring goes from alternator/regulator to the battery - no earth involved, the light earths through the alternator/regulator when the engine is not running and provides an exciter current to get the charging started - once the engine is running the charging voltage equals the battery voltage and the light goes out. |
| Chris at Octarine Services |
| So, tacho houses the ign light and the speedo houses the hi beam light? |
| Art Pearse |
| That's correct Art. |
| Steve Gyles |
| Since the IGN light has its own return wire, is it important to avoid grounding the bulb holder to the instrument case? |
| Art Pearse |
This thread was discussed between 30/10/2013 and 04/11/2013
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