Ignition and fuel warning lamps

[ian theobald]

Good day. I am in the process of reviewing fitting my dash board after recovering in New vinyl that came in trim kit
The wiring behind was a mess as various owners have spliced into wires over the years so have now put back as original in so far as connections.
The generator warning lamp terminations were all loose as was fuel warning lamp and in the process of trying to undo one of the lamps broke.
I was able to repair with epoxy but the fine windings all fell apart.
Would I be correct in assuming that it is there to reduce brightness of globes,that being the case could fit an external resistor like ballast resistors on 12v coils.
(Take note if ever fitting a new coil that it is a non ballast type or you end up with burnt points as I once discovered on my old Riley many yrs ago )
Was the intention to prevent red or green plastic from melting or a throw back from the war to keep all lighting dim?
Anyway I have lamps working and given the fact that only illuminate briefly hope won't be a problem.
Does any one know what resistance winding around the outside was as would be easy to fit an external resistor of modern type.
The other question is which way does panel and fog lamp switch rest.
I'm reluctant to disturb as difficult to loosen but at present the off position for both is horizontal.
If it helps I have found it helps when fitting the dash to have the Speedo and tachi removed and give the dash a gentle flex inwards at outer ends and fit up from under bottom corners thus not damaging piping or paint.
The fuel warning lamp although complete with spring etc has been retained with a small hose clamp due to my dash being thicker than original ,in the same manner as my ammeter which probably had some sort of retaining clip
Thanks .Ian

[Richard Michell]

Suggest you read this forum (my contribution is Post #26 and the link is to save me typing it out again). The resistor in series with these lamps is not to prevent plastic melting or to dull the bulb. https://www.mgexp.com/phorum/read.php?46,3816342,page=2

[ian theobald]

Thanks.i read your post and assume bulbs are not 2.5 volt but 2.5 watts
I'll have a talk to Auto electrician .as for fuel lamp ,I intend to use for indicators or high beam as even though it has a new sender has only ever come on once and was so dim could hardly see.
Now is nice and bright so can run wire from flasher relay to it.
Dip stick is best for fuel reading

[ian theobald]

What I have found out from a retired Auto electrician in my local vintage motorcycle club is to forget about all that and make the complex simple
Go and fit a 2 amp diode in series with a bit of heat shrink tubing .
If it is fitted the correct way the light will illuminate but prevent current flowing in reverse so will try that out as new lights are about 100 Aus.
He had heard of this happening but usually if motor was at higher than idling speed

[Richard Michell]

Ian, bulb is/was 2.5 volt. That is not an error. Resistance wire around the holder is/was in series with the bulb.

I am not an electrical expert but I believe that what your auto electrician says will work but would presumably then need a 12v bulb. However it is a moot point as to whether that mod is "making the complex simple". Your car, your call.

I agree that the running on phenomenon can/will only happen at higher idle speeds.

[ian theobald]

No offence to anyone but complex made simple for me is that dash bulbs not readily available but managed to find between 3 seperate shops in my home town enough 12volt watt globes for panel lights and 2 warning lamps.
I'm not sure if those 2.5volt lights are easy to get but was able to retain original lamp holders that would of cost over 200 dollars to replace.
These also would of needed to be ordered and posted.
The original bulb was a 12 volt and had no clue were 2,5
With a 2 dollar diode is a simple fix that no one will notice and old holders get to be saved
With the fuel warning light I think would be better to wire up to high beam for safety but original wires have used green power feed for blinkers and sender is tucked up beside so can easily be removed attached if ever required.
The wooden dip stick is best method for measuring fuel
Hope to soon be using the car after 6 months off the road retimbering
doors
As you can guess I'm not near a major city or MG supplier let alone another TC owner.
Just hope it was a positive suggestion or modification.
Bulbs are Narva part number47987 but doubt if Auto shops would restock as no longer common
Happy motoring .Ian

[Duncan M]

Same bulb as in most any "old fashioned" flashlight with two batteries. 2.2 to 2.5 volts. 0.2 to 0.5 watts is typical.

An article here:
http://ttypes.org/ttt2/one-of-lifes-little-mysteries

[ian theobald]

Good day,just an update.
Fortunately in our town of Nowra we have an electronics store selling mainly TV cable fittings and electronic components for hobbyist.
In there store they had the 2.5 v globes, insulated fine wire as well as led with same screw in thread but in the absence of any specific resistance readings for windings and the fragile state of the globe holder opted for the diode with 3 amp rating
Total cost was 75c and 1 dollar for 1 mtr white heat shrink tubing.
Much cheaper than the generic packets that sell various sizes in red and black in a pack.
Everything is now working so hopefully won't have to disturb the dash.
I can now fit all cables and front kick panels as long as they are correct but first need to tack piping under striker plates..
At least got to return use original bulb holders.
Both had 12volt globes previously.
It probably does not matter but my ignition light had the white wire terminated to the outside terminal which probably is correct as that supply's the power and has the original windings that were all but broken.
The only disappointment is even with 6 new panel lights the centre instruments can be barely seen in the dark much like before and will rely on the map lights as have done in the past.
I'm not sure about position of panel switches but can stay as is with off position being horizontal.
Final note is wiring circuit in my book does not show live wire to the clock
All my instruments were repaired in the late 90s so maybe the clock might work once connected as was not previously

[searunner]

Hi Ian
If you live in EU the better way to find one lamp reproduction are
https://www.s-v-c.co.uk/category/warning-lights/

a curiosity
some people are convinced that the warning light original color was BLUE
BUT it was GREEN and the age the day light and sun- transformed the color-on my TC 1946 is LIGHT BLUE

[TBrad]

Personally, I'd consider LEDs. They burn brighter, but far cooler and will never melt the lens.