3157 (dual) = Light is on and blinks when signal is used
7440 (single) = Light is off until signal is used

I think they can be interchanged as their connectors are the same, the dual filament is just what lets you have the dim light at night & turn signals at the same time.

I'm going to confirm this tomorrow when i pop out the bulbs for a closer look.

Also when you tested out the leds on the turn signals did you have to use load resistors to stop them from blinking too fast?

 

3156 is the single circuit version of the dual circuit 3157
And it's always better to get the dual circuit even if not needed.
And ... I'm pretty sure 7440 has a slightly different base.
It takes 2 minutes to pull one of your tails and look at the bulb u lazy person.

 

And yes, you need load resistors on turn signals to prevent hyperflash.

 

Serge I really tried but its just too dark, i will probably lose a screw or something, im hopelessly clumsy.

Anyhow, the more I think about it, I feel you are right...the led rear turn signals are not worth the hassle.

By the way, yesterday I ordered the GM door sills & step shields! So im pretty excited about those. I looked through your album and was really impressed by how they turned out.

 

Hey HyHoe:
Great look.

I was looking to do the same thing with the lower tail light and would lke your expertise. I assume you used the existing wiring harness but just ran a jumper wire from the side marker to the lower socket. Would you happen to know which wire was connnected on lower socket?

The GM engineers need their heads examined on this. Does not make any sense why the bottom is not leds too.

Thanks.

 

Hi D,

First let me reload the pic of them finished cause stupid MobileMe wiped all my pics:



I must confess my recollection of the wiring is poor as it was a while back ... but reading through my posts in this thread it seems we simply tapped into the side parking marker for the signal.

I'm sorry I can't be more specific but someone did this for me and my own wiring knowledge is non existent.

Hope that helps a tiny little.

 

Hi HyHoe,

Good enough. Thanks for your advice.

 

You're welcome,

I'm actually trying to remember if it was a 3157 socket/bulb in there or a 3156.
If it was a 56 then we changed both the connector and the bulb to 57s to allow for two signals.
If it was a 57, then we just connected it to the unused contact.

Cheers!

 

Just took it apart and tried connecting the brown wire from the side marker light to the yellow stop lamp. It worked but the turn signal did not. Had a 3156 bulb in it so I need a socket for the 3157.

I've looked around and can't find anything that will fit. Do you know where your guy got the sockets or can I get it from him?

Thank you.

 

I'm pretty sure one can get a 3157 socket and bulb from auto parts stores.
Or you can find them around the web: http://www.ebay.com/itm/2x-3157-LED-...382#vi-content

The only difference tween the 56 and the 57 is that the 57 is dual circuit and the 56 is single. So the 56 only has the one signal and the ground wheres the 57 has two separate signal and a ground. Same with the bulbs ... the 56 only has one filament inside whereas the 57 has two. The bulbs you can definitely find at your average parts store.

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Btw I'm just using that seller as an example, I'm not suggesting you should buy from them. But you do want the ones with the lead wires already in them cause it just makes it easier to wire/connect.