# LED Turn Signals - Need Diode Help !!!

#### D_B

Mar 8, 2012
7
Hi guys. When it comes to an automotive 12V DC system I know my way around. However, I have put together a system and I need a little help.

I am building a new front harness for my 1977 Corvette. I have chosen 1157, dual intensity LED front signal bulbs. The problem is that when one 'filament' is energized, power bleeds out from the other side, and vice versa.

This problem is keeping my signals from working properly when the headlights are on since the marker light circuit and the signal circuit share the same bulb.

Since they share the ground of the bulb socket I think my simple solution would be a diode inline with each of the power input wires to the socket of the 1157 LED bulb. My thinking is that if the power can only get in and ground out and not bleed out the wrong way everything will work as it's supposed to.

Yes, I understand an LED is in itself a diode, and it must sound silly to fix the problem with another diode. But, as I understand it, diodes only allow the flow of electricity in one direction and that's what I need so that power goes in to the bulb but not out.

So, first, does this theory stand up?

Second, how in the world do I choose a diode? These are LED bulbs so not much power is being used but there are so many options that go all the way down to milliamps I have no way of knowing what diode would be best suited for this project.

I will need a total of (4) diodes. One per power input wire. Since I have two sockets, two power input wires each, I need a diode per wire.

Thanks everyone, for putting up with another newb.

#### duke37

Jan 9, 2011
5,364
If an adjacent bulb lights when it should not, then you do not have a good ground. This is a very common problem.

If you still wish to go the diode route, you will need to know the current taken. The 1N500x series will carry 3A.

#### D_B

Mar 8, 2012
7
Operating Voltage Range is 9V - 14.8V.

Current draw @ 12V , mA, 24/82.

I copied the above specs from the website I bought them from. I understand the voltage range but I do not understand the current draw and how it translates into the diode I should get.

Is the 1N500x a diode series?

Thanks.

#### duke37

Jan 9, 2011
5,364
The 1N5400 = 50V
The 1N5408 =1000V

If your lights take 108mA then the 1A 1N400x series will do.

Have you checked the ground?

#### D_B

Mar 8, 2012
7
The 1N5400 = 50V
The 1N5408 =1000V

If your lights take 108mA then the 1A 1N400x series will do.

Have you checked the ground?

The grounds are perfect and overdone. I have done all of this myself. Multiple connections between battery, frame, and engine. The front harness, which I am building, has (3) grounds. Two of them are perimeter grounds to the frame and the third is a bridge ground tying the two harnesses together at the ground location where the two harnesses meet.

Will a chain store like Radio Shack carry a diode like the 1A 1N400X?

Thanks.

#### duke37

Jan 9, 2011
5,364
We do not have Radio Shack stores in the UK. Why don't you try their website?

#### jackorocko

Apr 4, 2010
1,284
yes radio shack carried them last I knew, always call and they will let you know for sure

#### D_B

Mar 8, 2012
7
yes radio shack carried them last I knew, always call and they will let you know for sure

Thank you. Bear with me, I know I am a tech tard when it comes to understanding these components. Just no experience with anything this specific.

First I tried Radio Shack's website. I searched for 1N400X and got nothing.

Second I called Radio Shack, and while he sounded like a typical young snot I would assume he would know something about what I was trying to do and I gave him the item in bold above and he said he couldn't find that item. I asked him if I had a number wrong and he said he didn't know because without a proper item number he couldn't look it up.

Don't sugar coat it, what did I get wrong?

Apr 4, 2010
1,284

#### D_B

Mar 8, 2012
7

I did the search for diode before and got the same results page, but I could not find a 1N400X.

Is that the wrong item number or a typo?

Thanks.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,506
Wow! Radio Shack are really expensive!

For just a couple of diodes it's not going to kill you, but, just.. WOW.

This is what most of us would consider a fair price. But for a couple of diodes the freight would kill you just as much I expect.

#### (*steve*)

##### ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,506
1N400x means something starting with 1N400 and followed by some other single character (in this case a digit).

So 1N4001, 1N4002, 1N4003, etc. Any will work fine for this.

It's a bit of shorthand that it's reasonable you were not aware of, but anyone selling electronic parts should be (forgive the poor old Radio Shack employee, he's probably waiting to move up to a job in MacDonalds).

#### D_B

Mar 8, 2012
7
1N400x means something starting with 1N400 and followed by some other single character (in this case a digit).

So 1N4001, 1N4002, 1N4003, etc. Any will work fine for this.

It's a bit of shorthand that it's reasonable you were not aware of, but anyone selling electronic parts should be (forgive the poor old Radio Shack employee, he's probably waiting to move up to a job in MacDonalds).

Steve, thank you. I didn't make the connection which is odd because we do it in the automotive world too. For example, the newest engine from GM is called the LS family. LS1, LS2, LS3, LS6...you get the point. Tons of options. When someone wants a blanket statement about the LS family they tend to shorthand it to LSx. I really feel stupid I didn't make that connection. I guess it's the never ending small part listing sequence for all those tiny components that make up electronics. There's an 'N' so why not an 'X' right?

Anyway, thanks for clearing that up. I'll head down to Radio Shack tomorrow and see what I can dig up.

#### duke37

Jan 9, 2011
5,364
x = ? Choose your pick!

The diodes can be 1N4001 to 1N4007
All you want is a 1A diode of almost any type and with a voltage capability of 50V or more for safety.
The 1N5400 to 1N5408 are 3A diodes.

I looked up the Radio Shack website, put in 'diode' and the first one shown was 1N4001

#### GreenGiant

Feb 9, 2012
842
I did the search for diode before and got the same results page, but I could not find a 1N400X.

Is that the wrong item number or a typo?

Thanks.

Search for 1N4001

or you could try www.digikey.com and search "1n400" and it should come up with 1N4001-1N4009

#### D_B

Mar 8, 2012
7
x = ? Choose your pick!

The diodes can be 1N4001 to 1N4007
All you want is a 1A diode of almost any type and with a voltage capability of 50V or more for safety.
The 1N5400 to 1N5408 are 3A diodes.

I looked up the Radio Shack website, put in 'diode' and the first one shown was 1N4001

Thanks everyone. I went and got two packs of (2) and already modified the harness using the diodes as described. Worked perfectly. One of them still had about a .10V bleed backwards but that's sure better than the 13V bleed from before.

Success is grand.

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