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MG MGA - Original gauge illumination level

How bright are the gauges supposed to be with stock bulbs? I've got the rheostat turned all the way up (and there are a few dead spots on it) and the speedomoter and tachometer are barely legible on a dark road. The odomoter isn't legible at all. The "safety" gague can be read if there are no oncoming cars or other bright lights, and the fuel gauge is somewhere between it and the tach/speedo. I know the MGA doesn't have a reputation for bright instruments, but this seems dim in the extreme. All new wiring, so that can't be the culprit. Should I clean the rheostat or is this normal?
David Breneman

Hi David. My MGA has always suffered from dim instrument lighting since it's initial rebuild. I also installed a new wiring harness. I am wondering if one could find small krypton bulbs that would fit the instrument lighting sockets? My headlights were also really dim, until I converted them over to quartz halogens. With the new bulbs, they are considerably brighter. My understanding is that the stock MGA charging system is marginal for supplying necessary power for the MGA lighting. Apparently big improvements in charging and lighting can be obtained by installing an alternator conversion. Having not installed an alternator, I cant say if this is actually true, although I suspect it probably is. Cheers! Glenn
Glenn

A few items of concern:

The insides of the gauge canisters are dirty leaving a lot less light to escape.
-you would have to dissassemble and paint white for good results here.

The old bulbs themselves are not producing the lumins that they are supposed to.
-replace these with new or at least clean the bulbs... possibly upgrade them at the same time.

The reostat on a number of different cars still takes away a little energy even when set all the way up.
-wire the wires together (placed on one side of the switch) and forget the reostat.

FWIW,
-BMC.
BMC Brian McCullough

I'm tired of dim gauges on my B and plan to change the rheostat to an on/off turn switch using the original knob to make it an invisible mod. I don't see any need to dim the dash lights, especially when full bright is already so low! A simple on/off is all that I find I need. I just need to find such a switch.

I wonder if the rheostat knob would fit an MGA headlamp switch? That would do it and you could wire it backwards so the dash light are on, and pulling turns them off. Or better yet, an early MGB map light switch.
Steve Simmons

Halagon bulbs for the dash are available from Little British Car Co. at: http://www.lbcarco.com/ . First follow Brian's advice of cleaning and painting the interior of the gauge housings and clean the lens while you have the housing apart. Second, remove the rheostat, and disassemble it by carefully bending up the three tabs for the back and remove it. Next remove the slider from the actual wire wound resistor (you may have to remove a circlip around the shaft to do this, I don't remember from when I did the on in our MGB) and take everything up to the kitchen and using a toothbrush and some really HOT water and detergent, scrub the living daylights out of the parts. Rinse everything with more really HOT water and shake all the water out, then pump in the oven set for the lowest temperature (or use a heat gun) to completely dry all of the components. When everything is dry, sue some very fine sand paper (600 grit) to polish the top of the wire that is the resistor. Lubricate the shaft and reassemble the rheostat and spray some contact cleaner/lubricant in through the coolins slots. You will be amazed at how well that rheostat works after this porcedure and while you are at it, you will notice how really bullet proof the rheostat is. Just by cleaning the rheostat, I was able to get enough light on my instruments that I no longer worry about getting halagon bulbs (oh yes, check that all the bulbs are working, or better, replace them all regardless - they aren't that expensive).

Steve, yes the knob will fit the MGB maplight switch (it is the same knob with a P and an arrow engraved in it. While you are cleaning up the rheostat, buff the knob up on a buffing wheel using some of the white "stainless" compound. Then clean all the compound out of the engraver P and arrow and run some white paint in them, it will make the knob look brand new.
Good luck - Dave
David DuBois

To follow Brian's lead: Clean the green plastic that filters the light onto the gauge face. Use a Q Tip slightly moistened with warm water. Also, make sure the brackets that not only retain the instrument but hold the bulb are in the correct positions directly over the green plastic slit and not off cue.

Surely new bulbs will produce better results.

Insure good earth connections--I'm not at the car right now but on the early B's the bracket that holds the gauge is the earth connection--against the fresh new paint of the facia!! You need to scratch the paint off the inside of the facia. I believe it's the same on the A's. hth

Paul
Paul Hanley

I'll try shorting the rheostat and see if that helps. If so, I'll undertake Dave's rheostat rebuilding procedure. I'm sure corrosion inside tha gauges isn't an issue as the "safety" gauge is new, the tachometer is NOS and the speedometer and fuel gauge were rebuilt. If the illumination level is still too low with the rheostat out of the loop, I'll look into the "upgraded" bulbs. Thanks, everyone!

David Breneman

I have the bulbs from LBC and they work great. Every guage is bright to the point I have to turn it down a little. I do have a Lucus alt. to provide extra power.
JEFF BECKER

Regarding Paul's suggestion to make sure that the ground points are doin their job, see my article on ground point preparation at: http://www.omgtr.ca/technical/General%20Technical/grounding.htm
Cheers - Dave
David DuBois

At full rheostat brightness the instruments are perfectly lit on my MGA. A drawback is the light that falls under the dash in the footwell area in my roadster (the coupes may not have this ambient light.) I'd like to keep this footwell area dark with the only light from the the guages. As most of this footwell light comes from the oil/temp guage and the fuel guage bulbs, I made a hood from thin wall ABS pipe that fits on the bulb holder brackets, and this hood is open at the place to direct the light at these instruments. The inside of the pipe tube is covered with chrome tape to make it more reflective. This improves the illumination of these guages and removes about 75% of the light falling into the footwell area. M.S.
Martin Straka

Interesting thread.

On the two main instruments, light reaches the instrument face through a radial gap of about one-tenth of an inch, between the edge of the face and the case. Between the face and the instrument glass, there's a circular mask, which hides this gap from any except a very oblique view; the underside of this mask is painted matt white. So is the underside of the instrument face itself.

Originally, the inside of the instrument case had a bright zinc-plated finish; about the same degree of reflectivity as the inside of a rattle-can top. It's hard to tell, but I don't think the case was polished internally. However, the receiving cup for the tell-tale lights certainly was.

After fifty years? Well, the white paint turns brown, and the plated finish dulls; easily remedied. Very different when new; out-of-town, that rheostat really was needed!

Martin - hope you haven't patented your light hoods, 'cos I'll be copying 'em!

Alex

A. W. Risk

I bead blased the reostat clean. It made a significant difference.
Arthur DiLello

An alternative to white paint for the "insides) of the gauges is "chrome" spray can paint available from Home Depot on this side of the pond. I recently refurbished a tail light on a Jag that was much darker that the one on the other side. Disassembly showed that the reflector surfaces had corroded and the reflective surface had peeled of over much of the area. A cleaning up with a find sand paper and spraying with the "chrome" paint resulted in a silvery surface that wasn't the totally smooth shiny surface of the original reflector. However, when installed there is now no noticible difference between the taillights, and the one no longer looks black during the day.

FWIW

Larry
58A - today's commuter car, mostly sunny and temp in the high 70s
Larry Hallanger

This thread was discussed between 15/12/2004 and 17/12/2004

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