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# Car lighting question: have a 6v constant with 12v flash

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#### UA///M3

##### Newbie level 4
6volts flash relay

Ok, well here is the situation. In my BMW 3 series for the parking lights and blinker, there is a single filament bulb. When I turn on the parking lights, there is a constant 6v signal and when I put the blinker on, there is a 12v signal sent for the bulb to blink. Basically, I do not want the parking lights to go on in the front for car show reasons, but I still want to retain my blinkers for when I am driving around. What can be done. I was thinking somewhere along the lines of a volt detector to detect only the 12v signal, but I have absolutely no idea of electronics. Any ideas would be great. thanks.

To distinguish between 6V and 12V you can build a simple circuit with a 10V zener diode and transistor/relay.
The relay's contact(s) will be activated if the input voltage is 12V whereas for 6V input nothing will happen .. see attached picture ..

Regards,
IanP

IanP said:
To distinguish between 6V and 12V you can build a simple circuit with a 10V zener diode and transistor/relay.
The relay's contact(s) will be activated if the input voltage is 12V whereas for 6V input nothing will happen .. see attached picture ..

Regards,
IanP

thanks, I understand what you're saying except how would I go about getting the materials. Like I said, Im very new to this and have not a clue, sorry, I looked at the diagram and wa like huh.lol. Would I be able to find the parts at Radio Shake and show them the diagram that you drew so they can explaine what part connects to what part and how to wire it up.

This circuit uses only commonly available parts, and Radio Shake for sure will have them ..
Just tell them what is this circuit for and show them the drawing ..

Regards,
IanP

Here are some hints:

Resistors:
1kΩ/0.25W
10kΩ/0.25W
Zener diode:
8.2V or 9.1V or 10V rated for 500mW or more (BZX79C10 , BZX85C10, 1N758, 1N4740 ..)
Diode (next to relay)
1N4001 .. 1N4004
Relay:
coil voltage 12V
contact current rating: as required by blinkers
Transistor:
capable of driving the above relay, for example: BD135, TIP120 ..

nice, thankyou so much. There have been ppl on my BMW forum who have been trying to figure this out for at least 2 years. They came up with running the blinkers off the side marker and putting in resistors. That idea puts strain on the Light Control Module because it overloads the sidemarker which may cause the LCM to fail (happend to a couple ppl already). Its like a \$700 piece and I dont feel like risking it doing it thier way.

IanP: ok, I went to Radio Shack to get all the parts. The lady seemd to find all the parts but couldnt understand the diagram you drew or the purpose of the Zenior Diode. She asked for a clearer diagram. She also said something about only using one relay that can handle both sides, left and right corner lights. Is it better to use 1 relay than 2? If I use one relay, then where would I have to connect the circuit to?

Also I have 3 wires going into 1 socket. Im guessing 1 is 12v, the other 6v, and the other ground. Could you include how I am supposed to connect the circuit to which wires and lable them. thanks a bunch.

1 more thing, I notice that you drew a switch in the diagram, bottom right. Is this an external switch that I will have to use? My headlight switch works like this: 1st positon is off, 2nd is parking lights, third is headlights with parking lights on. So if I do this circuit, will the second position parking light still work. I do want the parking lights to work in the back though.

First of all, that "switch" from bottom right is not a switch - these are the relay's contacts .
.
There are only 4 parts in that circuit and I can't imagine how to draw it "clearer"???

Anyhow, the funtion of the zener diode is to cut-off all volteges below zener voltage, in this case below 10V .. So transistor/relay will only be activated when the input voltage is above 10V +Ube(base-emitter≈0.7V)-->10.7V

My guess is that you should use 2 relays: one for the right side and one for the left side ..

Regards,
IanP

Heres some questions I drew out on the diagram. Sorry again for asking so many. I just want it to be clear for me when I do this tommorrow.

To make sure that we are talking about the same thing, could you draw a brief diagram of how are blinkers-parking lights-switches actually connected (before any modofication is undertaken) ..

For the time being I can explain the following points from your drawing:
1 = relay contacts ..
2 = nothing ..
3 = this end goes to +12V supply (battery) ..
4 = 0V
5 ==> after you supply your drawing ..
6 = NPN transistor ..

Regards,
IanP

hi this is very interesting to see you in this board this is to gain points only..sorry

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