Author Topic: Ignition light not coming on  (Read 2186 times)

Merc_Girl

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Ignition light not coming on
« on: November 16, 2022, 22:41:23 »
Hi folks
Other than the obvious, ie bulb has blown albeit as it’s a fairly new LED lamp, would anyone happen to know why an ignition has decided not to come on?

Was fine, but now nothing

With thanks in advance

Katie
230SL

BobH

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Re: Ignition light not coming on
« Reply #1 on: November 16, 2022, 23:30:57 »
Hello Katie, i assume you mean the charging light

Did you read this in the Tech Manual, regarding instrument lights?

Although some of these bulbs are straight swaps, there are a couple of points of attention regarding the alternator warning light and the low-fuel warning bulb.

The alternator warning light cannot be directly swapped for an LED, as this circuit specifically requires a 2W load (that of the incandescent bulb) for in order to work.
An additional resistor in parallel is required.
The expected 12V/2W incandescent bulb resistance is (12v * 12v / 2W =) 72ohms.
The 1-LED red bulb BA9S-R-90-12VAC is rated 0.02A at 12v (so 0.24W), so the resistance is about (12v / 0.02A =) 600ohms.
Therefore an 82ohm resistor in parallel with the LED is required ( based upon 1/72 = 1/600 + 1/82).
The resistor should be rated for at least 2W - a 5W 82ohm resistor (5% tolerance is fine) will be sufficient and readily available.
The low fuel warning lamp fitment appears too small to accommodate (currently available) BA9s base red LED.
Since this is a (presumably) very occasionally lit bulb it can expect to have a long life even as an incandescent and can be replaced by and original style incandescent.

Not sure what other owners have done, soldered a resistor across the LED, seems like a lot of work, i may be wrong, or stick with using a standard filament bulb?

Just read the Tech Manual further, seems there is a description of how and where to solder a resistor across the pins of the plug, so not a huge job
« Last Edit: November 17, 2022, 08:25:15 by BobH »
February 1965 230SL Automatic
UK delivered RHD
Papyrus white, blue hard top & hub caps
Blue soft top
Blue leather

Merc_Girl

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Re: Ignition light not coming on
« Reply #2 on: November 17, 2022, 09:35:37 »
Hi Bob
The little red light? 😁

I seem to remember not using an LED for that bulb, so I probably didn’t replace that one as would never go against the  eminent knowledge of others here, and certainly didn’t put a resistor in

Perhaps it is just the bulb that has blown (hopefully) as probably cheaper than alternative issues!

Thanks once again, much appreciated

Katie
230SL

BobH

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Re: Ignition light not coming on
« Reply #3 on: November 17, 2022, 10:00:56 »
Sometimes the spring at the bottom of the bulb holder needs a slight tweak, to give a bit more pressure against the bottom of the bulb, don't use anything metal to do this, something plastic or wooden, maybe a cocktail stick, once you've finished your drink, or disconnect the battery first, don't want any shorts
February 1965 230SL Automatic
UK delivered RHD
Papyrus white, blue hard top & hub caps
Blue soft top
Blue leather

Merc_Girl

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Re: Ignition light not coming on
« Reply #4 on: November 17, 2022, 23:13:48 »
Thanks Bob
Do you happen to know how to access ? Do I have to do a cotortionist act or is one able to access from the front?

Note your comment about shorting , but as I am short, does that apply 🤣🤣
230SL

teahead

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Re: Ignition light not coming on
« Reply #5 on: November 18, 2022, 03:44:46 »
gotta remove the tach 1st
1970 280SL auto, AC - aka "Edelweiss"

BobH

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Re: Ignition light not coming on
« Reply #6 on: November 18, 2022, 09:11:04 »
Hello Katie, from what i understand, regret not, be prepared for quite a battle. Have a search on here for advice and there are some excellent pictures in the Tech Manual, best description i found was here, posted by JA, but other owners may have other methods.  Once the instrument panel is out i would test all lamps using a 12V supply before you reassemble, don't want to have to do all of this twice.  Take a LOT of care removing the capillary tube and oil line, and don't start the car when the oil line is out

JA
Here is the sequence I always use in removing the instruments;

Remove the steering wheel, it comes of easily and makes the job so much easier. No puller required, just pop the center pad off and use a 22mm socket with extension to remove the nut. Note the slash mark on the end of the steering column, this indexes the installation position of the steering wheel during re-assembly. Next remove the cardboard dash under panel and the upholstered lower dash panel (three Phillips screws). Next remove the electrical plug terminal bracket by unfastening the two phillips screws and move it out of the way. Reach you hand up through the new opening and pull the small defroster vent tube off and out of the way. Unscrew the tachometer cable. Unscrew the thumbscrew holding the tachometer in place. Remove the tach after popping out the two light bulb assemblies. After the tach is removed you have easy access to the thumbscrews holding the center cluster in place. You will need to unfasten the 10mm oil pressure line before removing the center cluster from the dash. The temperature gauge line is not a wire but a small capillary tube. Handle it with care. If the tube is crimped or broken the gauge will no longer function. To continue, remove the small slotted screw at the top back of the cluster. This will allow you to remove the back of the center cluster and you will be able to unfasten the temp gauge and leave it connected in the dash. Be careful when you re-install this, if you do not have the shaft for the dimmer lined up with the knob you can break the glass when you tighten down the slotted screw. Check  the dimmer and treat it with some contact cleaner and lube (radio shack) while you have this out. At this point you have easy access to the speedometer and ignition switch if you they need service.

Be sure not to srart the engine while the oil pressure gauge is disconnected, you and your pagoda will get an oil bath! During re-assembly pay attention that the brown ground wire with the ring terminal is placed under the tachometer and speedometer thumbscrews before installation of their brackets, or their lights will not work. Check the lighting before you put everything back together!

Joe Alexander
Blacklick, Ohio
February 1965 230SL Automatic
UK delivered RHD
Papyrus white, blue hard top & hub caps
Blue soft top
Blue leather

Paul & Dolly

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Re: Ignition light not coming on
« Reply #7 on: November 18, 2022, 20:54:50 »
Katie.
Set the wipers to vertical, and disconnect the battery before you do anything else.
The RHD procedure can be different to the LHD instructions.

Good luck

Paul

Paul (located in Cardiff - Wales - UK)
1967 Early 250 SL (Auto) White
Mitsubishi i Car
Toyota RAV 4  Hybrid AWD
1936 Alvis Firebird (Gone............)

Merc_Girl

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Re: Ignition light not coming on
« Reply #8 on: November 19, 2022, 00:44:40 »
Wow! All this for a bulb!

Thanks everyone, will follow instructions with great care 🙂
230SL

teahead

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Re: Ignition light not coming on
« Reply #9 on: November 19, 2022, 18:15:14 »
curious, how were you able to remove that center gauge cluster to replace the bulb w/LED if you didn't remove the tach?
1970 280SL auto, AC - aka "Edelweiss"

Merc_Girl

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Re: Ignition light not coming on
« Reply #10 on: November 19, 2022, 21:40:16 »
curious, how were you able to remove that center gauge cluster to replace the bulb w/LED if you didn't remove the tach?

I didn’t. Bessy was already at the garage at the time and I asked them to fit 😁
230SL