Do you know how to upgrade an S-Helper SW9 headlight to LED? Thanks.

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Marty

Thanks for the helpful replies and posts.  I measured the output voltage at the posts onto which the headlight lead-wire plug gets inserted -- 4.0-12.5 VDC based on 8.3-15.8VAC applied to the tracks.  So it seems I need to use a 3mm, 20mA, bright white or golden white LED with a 100 to 1000 ohm resistor installed inline to the + LED post depending on how bright I want the LED to illuminate.  Sound about right to you?  

PS There isn't much room in the engine up close to the bulb/LED, so I'll need to splice the resistor into the wire leading up to the LED.  The pre-installed units look convenient, but the resistor is installed too close the LED.

Thanks.  Will do.  Do you also recommend installing a diode to prevent reverse voltage damage or is that a moot point with DC source voltage?  I've read where white LED's are apparently particularly sensitive to that and even static electricity.  Thanks.  

Thanks Mark that helps a lot.  Interesting how that shows the reverse voltage preventing diode installed essentially across the leads of the LED, not in-line with the resistor as I have also seen diagrammed.  I think when the source voltage is AC you must install it across the leads (essentially converting AC to DC), and if DC source then inline with the resistor to be extra cautious -- see here for example at  Electric Railroad under Hint's and Tips, Installing LED's on the Outputs.  I agree with you though, if with DC source for something to be reverse voltage you've probably got bigger problems than with your lighting.