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MG TD TF 1500 - dropping resistor installed,where's the bulb?

hello, i have purchased and soldered in a 68 ohm, 2 watt dropping resistor into my low fuel level circuit, now where do i find the 12v .5 watt bulb? regards, tom
tom peterson

Tom -- The bulb is G987 12 volt 2.2 watt I calculate it at 0.183 amps. a very close equivalent would be a #1449 bulb (Radio Shack #RSU 11910783). A bulb #1487 has the same electrical specs but I am not sure of the socket.

I hope this helps.

Bob
R. K. (Bob) Jeffers

Sorry, Tom, but with the resistor in place you don't want a 12 volt bulb. The bulb that you want is one that is rated at 2 or 2.5 volts at about .2 amps, about .5 watts.
The 987 type of bulb may well work, but at a diminished brightness.
Bud Krueger

thank you bob and bud. bud, of course you are correct..the maintenance manual says the same ..i have read it..and still i wrote 12v. jeeezzz..thanks for getting me back on track..so my question remains..where are all of the 2.5 volt .5 watt bulbs? i will check radio shack. regards, tom
tom peterson

ok, i just bought 8 on ebay for $4.25 including shipping. i can't drive my car out of the driveway for that and these are coming from alaska. regards, tom
tom peterson

Tom P. -- Can you give me a page No. and /or para No. where the WSM talks about a 2 volt bulb??
Thanks in Advance.

Bob
R. K. (Bob) Jeffers

You got me, Bob. The WSM (page N.18) only speaks of #987, 12v, 2.2 W bulbs.
Bud Krueger

bud and bob, i have two WSM's. the early one does not mention fuel warning bulb, only ignition, but the second WSM, dated 1/54 for both TD's and TF's, on page N18, bottom of the page in a boxed section labeled "replacement bulbs" it lists: "ignition, fuel and headlamp warning light...lucas 970...2.5 volts... .5 watt" regards, tom
tom peterson

Tom - The bulb you are looking for is a #14. The brand that I got is Wagner. Radio Shack will probably not carry them. You will have to try some places like Digi Key https://sales.digikey.com MCM http://www.mcmelectronics.com or even Antique Electronic Supply http://www.tubesandmore.com/ Cheers - Dave
David DuBois

Tom -- We have run onto something very interesting here. My copy of the WSM dated issue 4 (H&E) 91826 2/55 lists the Ignition,fuel and headlamp beam warning light as 987 12 volt 2.2 watts. Let me check my other copy.

Nope it's dated the same as the first and the bulb is listed the same. Gives us a real dilema.

Could it be that they changed the resistor on the sockets for a while and spec'ed the 2.5 volt bulb then realized the problem they had created and went back. Has to be something like that because my WSM's are dated later than yours.

Me, I don't know!

Cheers,

Bob
R. K. (Bob) Jeffers

I plead ignorance on that since I have always had 12 V bulbs and I am happy with them. No resistor of course.

Denis, 1950 TD
Denis L. Baggi

Bob and Denis - Out TD came with a 2.5 volt bulb for the low fuel indicator, but judging from the number of cars that came with 12 volt bulbs, I have to assume that either it was a mixed set up on the cars (particularly when Tom found a reference to the 2.5 volt bulbs in one printing of the shop manual). It makes me wonder if, at some point, the bulbs were changed to 12 volts, but the resistor was left in to cut the brightness down. I added additional resistance to the socket in our car (using the 2.5 volt bulbs) because I found the the original set up was so bright that it was a problem at night if I ran low on fuel. Cheers - Dave
David DuBois

Okay, Bob, couldn't find the right condiments to go with the crow. Went up to the garage and looked through some of my WSM copies. Attached below is a copy of page N.18 of the WSM, Issue 2 (Export)79345 -- 1/53. It clearly shows the Ignition, fuel and headlamp beam warning light as a Lucas No. 970 bulb, 2.5 volts, 0.5 watts.

Why there may have been a change to a 2.2w, 12v bulb is a puzzler to this retired electro-optics engineer. If you look at http://www.ttalk.info/Tech/Indicators.html you'll see that I tried a 987 lamp. It was visible, but not what a photonics person would use for the application. Probably fine at night, but I'm not sure you'd notice in the daytime. Must admit to having seen TD once with a small piece of friction tape on the inside of the green lens so as to obscure a direct view of the filament. In fact, it was my car.

Bud Krueger

Ignition lamp has whatever was in there in 1978 when the car was put away... Heater warning bulb is a 12 V from local parts store a month or so ago!

gblawson(gordon)

Since everybody is talking about bulbs with low voltage and resistors in series, why not experiment with LED's? Then the need for replacement would hardly come up.
Denis L. Baggi

Everyone is still looking for inexpensive positive ground leds
gblawson(gordon)

I also kind of like going out and going for a drive in something that is all '53... no plastic, no computer, no 'ultra bright' LED's, and thank god no 'sensors' to tell me my license plate light is out!!!!

We seem to be selective in our 'originality' stuff... keep seeing rubber bumper MGB's with navigation installations and those radios that spin and shake !!!! Driving the TD is a way to get away from all that sxxxt!

Photo of Nav installation!

gblawson(gordon)

I tend to be a purist but I make exceptions, as long as:

- the "feel" of the car when driving is unaffected (hence, no change of motor, even gearbox)
- the modification is barely visible
- it is easy to restore everything to what it was.

I'd say that using LEDs' instead of filament bulbs satisfy my criteria for "originality".

Denis, 1950 MG (truly "original")
Denis L. Baggi

"gblawson(gordon), Ontario, Canada
Everyone is still looking for inexpensive positive ground leds"

No, I mean loose leads those you buy in an electronic store for a few cents, then you fit them in the socket for ignition, low fuel level etc. Not headlights.
Denis L. Baggi

Yes, I know what you meant... led's have to be pos grounded or they won't work? If you have changed to neg ground there is no problem.
gblawson(gordon)

Welllll... not quite that simple. A single LED will typically drop about 2 volts across it at normal operating current, i.e., in the tens of mA range. Our Ignition/Fuel sockets have about 70-80 ohms of resistance connected up to the 12 volts. This will be the factor to determine the current in the circuit, on the order of 100+mA. Enough to wipe out the LED if there's no other current limiter in the circuit. You can't just solder the LED into an old bulb shell and plug it in. That holds for either ground.
Bud Krueger

This thread was discussed between 27/05/2008 and 31/05/2008

MG TD TF 1500 index

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