Jump to content

Roadmaster Mirror Compass Bulb


padgett

Recommended Posts

Thought I had this but all I can find are installation instructions. Does anyone know what the bulb is that lights the compass display and how to replace it ? The Roadmaster unit is perfect for a convertible in sunlight but needs the backlight at night or when the top is up.

Alternately does anyone have a nice one for sale that all bulbs work ? Do not need autodim, just maplights and compass.

Link to comment
Share on other sites

Not sure what size the bulb is. But you access it by prying out the map light. (Small screwdriver into the little slot.) It, or its holder, is glued in with a dab of what appears to be some sort of silicone. I'd like to know too - as I have a spare that needs one. Just have not got enough 'round 2 its...

Link to comment
Share on other sites

OK the whole switch/light assembly comes out and then the black bulb holder is in the white socket (removed from socket below). Now does the bulb pull out of the rubber surround and what is its replacement please ? Anyone know ?

post-31022-143139184629_thumb.jpg

Link to comment
Share on other sites

Guest Richard D

Padgett, That looks like the bulb used in my 90's doors above the interior door handle, I just looked in my small bulb drawer and it might be a 1891. Perhaps you could look it up in the FSW

R.

Link to comment
Share on other sites

Guest Mc_Reatta

Suspect that lead broke off flush with the glass envelope so I would say ala Tony Soprano "forgetaboutit"

I would suggest trying Rat Shack and see if one of these is close enough for government work:

12V/50mA Incandescent Bulb : Incandescent Bulbs | RadioShack.com

12V/25mA Miniature Lamps : Miniature Lamps | RadioShack.com

Otherwise find a local electronics shop or go onto the "bay of e" and seek a replacement. Check for bulb of same size, 12 to 14 volts, the more the amp rating, the brighter the output.

If your really game, get a high output LED something like:

NTE30044 White Super-bright LED Indicator : LED Indicators | RadioShack.com

an connect a 330 ohm 1/2 watt resistor in series with it to your two blue leads.

Will need to figure out which lead is positive so you don't wire in the LED backwards.

Link to comment
Share on other sites

Guest Richard D

Sorry Padgett, you were correct, I had the scale all wrong. I too recommend a Radio Shack grain o wheat lamp or a white LED with an eight hundred ohm resistor in series.

Link to comment
Share on other sites

  • 2 weeks later...

Padgett: Any luck yet?

I think I am going the LED route. Considering that there is a blue filter in the lamp housing, I think a blue LED will be a better choice than a white one.

Mc_Reatta: The LEDs I am considering would probably want more like a 560 ohm resistor, rather than 330. (Assumptions: 14v for the car, 3.5v on the LED with a 20ma current draw.)

Link to comment
Share on other sites

Guest Mc_Reatta
Padgett: Any luck yet?

I think I am going the LED route. Considering that there is a blue filter in the lamp housing, I think a blue LED will be a better choice than a white one.

Mc_Reatta: The LEDs I am considering would probably want more like a 560 ohm resistor, rather than 330. (Assumptions: 14v for the car, 3.5v on the LED with a 20ma current draw.)

I concur with your calculations. Most important value in the equation is the current draw. If too high it will shorten the life of the LED, to low and LED will not light. Within limits, the LED can be dimmed if needed by keeping the current draw below the specified limit by increasing the resistor value.

Link to comment
Share on other sites

I concur with your calculations. Most important value in the equation is the current draw. If too high it will shorten the life of the LED, to low and LED will not light. Within limits, the LED can be dimmed if needed by keeping the current draw below the specified limit by increasing the resistor value.

I bought a Rat Shak blue LED #276-0316. Also realized I had a couple of #276-0311 at home - intended for another project that I haven't got around to. The latter ones are rated to want a 30ma draw across 5v - and as you suggested, a 330 ohm resistor would be proper for them.

I will try both to see which works best. I suspect the first one will - mostly because it has a wider viewing angle than the latter. (30 degrees vs 24 degrees.) OTOH, it may end up being too bright. Unfortunately, I won't be able to get to them for a few days. Will report back when I do. If neither of these works, I will head over to a Real parts place. (Several good ones here in Silicon Valley.)

Link to comment
Share on other sites

FWIW I repaired a few of these in the past using a white T-1 LED and a dropping resistor. The value of the resistor escapes me at the moment. Keep in mind a blue LED will result in a much less legible display, as it is an LCD (black text on light background) and as blue LEDS tend to be a "royal blue" shade, not light blue, the contrast will be poor. A white LED was just about perfect in terms of the backlight. Plenty bright to see, but not so bright as to be obnoxious during night driving.

If using an LED, polarity is important. Make sure you identify the negative lead on the lamp by continuity testing between the lamp connector terminals and the main ground on the mirror harness (all black wire with no color stripe). The connector used is much like those that used to be put on cordless phone battery packs before they all went to standard AA or AAA rechargeable batteries. I usually cut the lamp off, use the connector and remnant of the lamp lead wires, solder the dropping resistor in-line and heat shrink it. A T-1 size led fits in the existing rubber grommet but is rather snug. a T-1 3/4 size (the standard round size LED) is far too large.

Also, be very careful with the plastic reflector housing as it will break easily from being brittle from the years of heat from the original lamp. I've had to hot-glue a couple to hold it all together.

KDirk

Link to comment
Share on other sites

Padgett,

no, have not used any incandescent replacement due to concerns over heat. That and the LED will last virtually forever so didn't see the need to go with a regular bulb in this application. Based on the condition of the plastic reflector behind the display, I'd say heat was an issue with the original bulb as well (over 15-20 years anyway). Another thing that could be done is to find a 14 volt bulb (I think I have seen very small "grain of wheat" lamps in 14V spec) as it would run cooler than a 12V bulb (cars voltage should be about 13.5 anyway) and last longer. 14 Being a non-standard voltage would make it harder to source, of course.

KDirk

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...