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LED dash light problem
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Jasonhall1980
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PostPosted: Tue Jan 31, 2023 2:16 pm    Post subject: LED dash light problem Reply with quote

Hey all,

I’ve bought LED dash lights for my 1959 beetle. It’s a 6v system still. I bought 12v lights after researching and finding they should work. Nothing lit up, but when turning the key off, they flashed. This told me, potentially reversed polarity. I couldn’t get them to work.

I later bought LEDs that specified they would work for 6v or 12v. After installed them, same thing. They flash when the key is turned off.

Just to clarify, only the Gen and oil pressure flash.

Any ideas?

I want LEDs for 2 reasons. Correct color without changing lenses and brightness. I understand some of you feel incandescent is bright enough, but I don’t feel that way. Just to save the “why not use incandescent” responses.
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RLFD213
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PostPosted: Tue Jan 31, 2023 2:25 pm    Post subject: Re: LED dash light problem Reply with quote

If the generator is like the alternator you’re gonna need a regular bulb somewhere in the wiring. The bulb is what tells the generator to start charging and LEDs don’t draw enough to do that. It sounds like yours is close but not enough. Try putting a regular bulb in and see if it still happens
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ashman40
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PostPosted: Tue Jan 31, 2023 3:03 pm    Post subject: Re: LED dash light problem Reply with quote

I'm not very familiar with the pre-60's Beetles, but from the wiring diagram they appear to have the same 3 indicator lamp housing at the bottom of the speedometer that isolates/insulates the 3 bulb holders from the grounded case of the speedometer. This allows these 3 bulbs to operate differently from the other bulbs in the speedometer which ground to the case of the speedometer.
Here is a mid-60's speedometer, I'm hoping yours is similar.
Image may have been reduced in size. Click image to view fullscreen.


The common wire (C) connected to the U-shaped metal conductor allows a single fuse box powered black wire connected to the C terminal to provide a common 12v+ to the sides of all three bulb holders. This means the male terminal at the end of each of these 3 bulb holder connects to a switched ground that grounds the bulb in the holder to turn it ON.

The stock incandescent bulbs used in these bulb holders don't care which direction current flows thru them. As long as current flows in one direction the filament will heat up and the bulb will turn ON.

If you are using LED bulbs which are polarized (only allow current to flow in one direction) they must be oriented so positive current may flow into the side of the bulb and the base conductor is grounded. Most small LEDs expect positive current to flow into the base conductor and the sides of the bulb are grounded.

You have 3 options which I can think of:
    1) Find LED bulbs that are not biased for current flow. Some of the newer LEDs have small circuits built in that manage the current flow and do not care which direction the incoming current flows. But I have not yet seen very small LEDs that fit into the stock bulb holders that are non-polarized.

    2) Use stock bulb holders that have 2 terminals. These were used in the later speedometers with EGR systems. The specialized bulb holder has two terminals and does not ground thru the body of the speedometer. The here wires can be swapped to control which direction the current flows.
    https://www.wolfsburgwest.com/cart/DetailsList.cfm?ID=113957397
    Image may have been reduced in size. Click image to view fullscreen.


    3) Use non-stock type LED bulbs that have 2-wire plugs that you can wire independent of the speedometer bulb holder. They needs to be slim enough to slide into the opening and you may need to insulate the sides to prevent them from shorting out to the speedometer case. They do come in red and green colored lamps. Though, I'm just not sure how bright they are.
    https://www.superbrightleds.com/vehicle-lights/led...wedge-base
    With this 2-wire bulb holder:
    https://www.superbrightleds.com/t1-3-4-wedge-base-socket-wired-74-socket

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'67 Beetle #1 {project car that never made it to the road Sad }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}
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Jasonhall1980
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PostPosted: Tue Jan 31, 2023 3:44 pm    Post subject: Re: LED dash light problem Reply with quote

Ashman40! That explains a ton. Thank you. With all that being said, oil pressure light works in reverse correct? As in once grounded it goes out.
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EVfun
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PostPosted: Tue Jan 31, 2023 5:11 pm    Post subject: Re: LED dash light problem Reply with quote

Oil pressure, Generator, and turn signal lamps all work in reverse from normal (normal being the outside body of the bulb to negative ground). You can buy reverse polarity LED dash lights and use your stock holder too.

I want to thank Ashman40 for pointing out the late 2 terminal bulb holder. I didn't know about that and it could prove useful in a number of situations. I'm thinking what could be done with a bi-color LED...
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ashman40
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PostPosted: Wed Feb 01, 2023 5:20 pm    Post subject: Re: LED dash light problem Reply with quote

Jasonhall1980 wrote:
With all that being said, oil pressure light works in reverse correct? As in once grounded it goes out.

The OIL lamp is the simplest of the 3 bulbs... it is powered while the ignition switch is ON and the blue/green wire from the bulb holder to the oil pressure switch is grounded when the engine oil pressure drops below 5psi. Positive current only ever runs from the fuse box to the oil pressure switch.

The GEN lamp USUALLY work in the same way... ground the wire and the bulb turns ON. But there are a few conditions when it works with current flowing in the opposite direction (remember incandescent bulbs don't care which direction current flows thru them)...

GEN lamp :
ON with ignition ON before the engine is running. The VR grounds the blue #61 wire.
OFF when the engine is running. The VR outputs 12v+ on the #61 terminal. This 12v+ is the same (or nearly the same) as the 12v+ coming from the fuse box. The GEN lamp sees 12v+ from both directions so no current flows thru the bulb and it remains OFF.
ON when the output from the generator exceeds the output from the battery. For example, 16v+ from the VR on the #61 terminal vs. 12v+ from the battery/fuse box means 4v flowing from the VR to the fuse box backwards thru the GEN lamp... it turns ON to notify you that the generator is overcharging. The LED bulb in the GEN lamp may not turn ON when this imbalance happens.
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'67 Beetle #1 {project car that never made it to the road Sad }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}
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mukluk
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PostPosted: Wed Feb 01, 2023 8:03 pm    Post subject: Re: LED dash light problem Reply with quote

ashman40 wrote:
The GEN lamp USUALLY work in the same way... ground the wire and the bulb turns ON. But there are a few conditions when it works with current flowing in the opposite direction (remember incandescent bulbs don't care which direction current flows thru them)...

GEN lamp :
ON with ignition ON before the engine is running. The VR grounds the blue #61 wire.
OFF when the engine is running. The VR outputs 12v+ on the #61 terminal. This 12v+ is the same (or nearly the same) as the 12v+ coming from the fuse box. The GEN lamp sees 12v+ from both directions so no current flows thru the bulb and it remains OFF.
ON when the output from the generator exceeds the output from the battery. For example, 16v+ from the VR on the #61 terminal vs. 12v+ from the battery/fuse box means 4v flowing from the VR to the fuse box backwards thru the GEN lamp... it turns ON to notify you that the generator is overcharging. The LED bulb in the GEN lamp may not turn ON when this imbalance happens.

Most importantly, the GEN light will illuminate with the engine running if the fan belt breaks, alerting the driver they've lost cooling air to the engine. Similarly, the GEN light will come on with the engine running if the charging system stops working -- at least in this latter case it's still safe to run the engine since the fan is still being spun, but the car will be operating solely on the battery.
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