Daytime running lights / high beam

Maybe this can be done without Arduino I'm definitely hoping to simplify.

I've got a new car with a 9005 bulb that operates both as a high beam (12V) and a daytime running light (8v) depending on various situations controlled by the car. Independently, I'm replacing the low beam with an HID Bi-Xenon projector that houses a solenoid requiring 12V to operate the high beam shield.

How can I take the 9005 bulb leads that vary in voltage 12v/8v/0v (high/drl/off) to only supply 12v/0v to the solenoid (high/off) to operate the bi-xenon cutoff shield for the high beam? I basically want the solenoid to not see any current unless it's 12V.

Just use a small relay with the coil controlled by the high-beam switch. Use a diode across the coil of the relay in case you have a semiconductor (e.g. a transistor) in a body control module.

FYI here is the wiring diagram from the car with the resistor that drops the voltage for the DRL.

Blackfin:
Just use a small relay with the coil controlled by the high-beam switch. Use a diode across the coil of the relay in case you have a semiconductor (e.g. a transistor) in a body control module.

when you mean "high beam switch", you mean the positive wire on the 9005 bulb to a relay with a diode? or you mean separately find the high beam switch somewhere in my car's wiring.

You might want to see if the car's ECM "knows" if the lights are off, on, or high. If the ECM know's then looking to find a tap for the signal will be quite a bit easier. Of course, reading the ECM ODBCII coeds adds complexity but it is a complexity that allows for expansion.

Your new car doubtlessly has circuits to determine when a bulb is burned out. Will your change effect it?

Paul

bigbangus:
FYI here is the wiring diagram from the car with the resistor that drops the voltage for the DRL.

I feel like we're missing part of the picture.

In what must be a similar architecture to yours, my 2010 STi's 9005 high beam bulbs serves as the DRL bulbs. When driving around in the daytime, the bulbs are driven at some percentage of full-power.

However, when I raise the handbrake, the bulbs go out. When I have the low-beams turned on, the bulbs go out. When I move the steering column stalk to high-beam (or flash to pass) the bulbs come on at full power.

With what you're showing, the bulbs are either on at reduced brightness through the resistor or, if the DRL relay is switched, full brightness from 12V (resistor bypassed.) How are the bulbs otherwise controlled so they go off in the conditions I mentioned above?

Or do they not go off; they're either always on at DRL or full-bright levels?

Paul_KD7HB:
Your new car doubtlessly has circuits to determine when a bulb is burned out. Will your change effect it?

Paul

Just unplugged the 9005 DRL / high beam bulbs and activated the high beams. Car didn't report anything. Drove around for a bit. Nothing.

Blackfin:
Or do they not go off; they're either always on at DRL or full-bright levels?

In this case it's a 2021 Subaru Crosstrek Sport. And yes the response is the same as your car. Either high/drl/off.
So by adding a relay as you describe controlled by the 9005 wire, when the voltage is 8V instead of 12V, it will be benign to the relay? And the relay will only operate when it sees full 12V (high beam)? That's my goal.

Well, I looked at the wiring diagram for my STi; I know it's 11 years (!) earlier than yours but I suspect the logic is similar.

On mine the feed for the DRL relay comes from fuse #7 (as does yours) which, in turn, derives power from the "headlight relay hi" (HRH). That is switched by the BIU (body integrated unit.)

For your solenoid, you basically need to know when the HRH is energized AND when the DRL relay is set to bypass the dimming resistor (not sure if this is the energized or de-energized state.)

In theory, this logic simplifies to looking at the bypass path out of the DRL relay: If it's hot both relays are in the state to turn on the high-beam and you want to pull in your solenoid. If it's low it means either the DRL relay is powering the dimming resistor path OR that the HRH is off. In either case, you don't want the solenoid pulled in.

A problem you face is that the high-beam output of the DRL relay will show 8V (or whatever the dimmed voltage is) because the two nets join at the resistor.

My suggestion would be then (without thinking too deeply) to wire your relay as:

  • pin 30 tapped into the GW wire at terminal 5 of your DRL relay
  • pin 87 to the +ve side of your solenoid (the other side of your solenoid to GND)
  • pin 86 to pin 30
  • pin 85 tapped into the LY wire connected to terminal 3 of the DRL relay

The HRH relay supplies the power that will energize the solenoid (30 to 87 when the relay is closed).

The HRH also provides the top-side power for the solenoid relay by connecting pin 86 to pin 30.

Pin 3 of the DRL relay is grounded when the BIU want to enable the highbeam/disable the DRL. So it can provide the ground path for the solenoid relay.

Power is only there when the HRH is closed. The solenoid relay is only switched when the BIU switches to headlight (from daytime running light) mode.

YMMV.

bigbangus:
In this case it's a 2021 Subaru Crosstrek Sport. And yes the response is the same as your car. Either high/drl/off.
So by adding a relay as you describe controlled by the 9005 wire, when the voltage is 8V instead of 12V, it will be benign to the relay? And the relay will only operate when it sees full 12V (high beam)? That's my goal.

Don't know which country you are from but in many, any motor vehicle modifications would require certification or else face the possibility of zero insurance in event of an accident not to mention the attention of the local constabulary.
I believe Arduino also have a condition clause where the use in life threatening situations is prohibited.
You may well say, what life threatening situation.
I ,for one, would not like to be on the receiving end of hid lights at full blast on any highway.

The most socially responsible thing to do with the DRLs is to disconnect the resistor. :roll_eyes:

Blackfin:
Well, I looked at the wiring diagram for my STi; I know it's 11 years (!) earlier than yours but I suspect the logic is similar.

On mine the feed for the DRL relay comes from fuse #7 (as does yours) which, in turn, derives power from the "headlight relay hi" (HRH). That is switched by the BIU (body integrated unit.)

For your solenoid, you basically need to know when the HRH is energized AND when the DRL relay is set to bypass the dimming resistor (not sure if this is the energized or de-energized state.)

In theory, this logic simplifies to looking at the bypass path out of the DRL relay: If it's hot both relays are in the state to turn on the high-beam and you want to pull in your solenoid. If it's low it means either the DRL relay is powering the dimming resistor path OR that the HRH is off. In either case, you don't want the solenoid pulled in.

A problem you face is that the high-beam output of the DRL relay will show 8V (or whatever the dimmed voltage is) because the two nets join at the resistor.

My suggestion would be then (without thinking too deeply) to wire your relay as:

  • pin 30 tapped into the GW wire at terminal 5 of your DRL relay
  • pin 87 to the +ve side of your solenoid (the other side of your solenoid to GND)
  • pin 86 to pin 30
  • pin 85 tapped into the LY wire connected to terminal 3 of the DRL relay

The HRH relay supplies the power that will energize the solenoid (30 to 87 when the relay is closed).

The HRH also provides the top-side power for the solenoid relay by connecting pin 86 to pin 30.

Pin 3 of the DRL relay is grounded when the BIU want to enable the highbeam/disable the DRL. So it can provide the ground path for the solenoid relay.

Power is only there when the HRH is closed. The solenoid relay is only switched when the BIU switches to headlight (from daytime running light) mode.

YMMV.

So I found on HID planet that I'm not alone. Consensus is that if DRL is through a resistor just plug the bi-xenon solenoid to the high beam / DRL and just let it be. Shouldn't hurt it.
Otherwise, you can do the following:
85 goes to low beam negative
86 goes to low beam positive
87 goes to bixenon solenoid
30 goes to high beam positive

Since the low beam and DRL are exclusive, using the low beam as the relay switch makes sense to isolate any condition when the DRL is on...

bigbangus:
https://www.hidplanet.com/forums/forum/general-discussion/general-discussion-aa/32927-how-do-i-wire-the-fx-r-solenoid-to-my-drl-high-beams
So I found on HID planet that I'm not alone. Consensus is that if DRL is through a resistor just plug the bi-xenon solenoid to the high beam / DRL and just let it be. Shouldn't hurt it.

Thinking out loud:

I think a 9005 bulb is rated 65-watts at 12.8V which means a current of at least 5A per side, giving an approximate "hot" resistance of 2.56-ohms. With two of these in parallel (left and right), the net resistance is 1.28-ohm.

From what I've been able to find on NASIOC it looks like the DRL resistor is ca. 1.13-ohms (that was a 2008 model; YMMV...)

With the DRL resistor in series, the circuit resistance is then ~1.28-ohm + 1.13-ohm or 2.41-ohm. (The 1.28 figure could be lower with the bulbs at a cooler operating temperature.) At 12.8V the current is 5.3A. This gives a voltage drop across the DRL resistor of 6V.

Depending on the resistance of the two shutter solenoids they would see something like 6V during "DRL" operation (their resistance then ends up in parallel with the two 9005 bulbs reducing the overall resistance downstream of the DRL resistor...)

It would be interesting to connect a variable power supply to the solenoids and see what their pull-in voltage & current is to see how close they are to activating on DRL power. It would also be interesting to measure their resistance to understand the continuous Pd (power dissipation) they'd see with ~6V DRL voltage at their terminal.

There are “ soft issues” .....And don’t forget this will affect you cars warranty ... likely they won’t cover any future electrical faults !

There is also the safety issue , if your headlamps go out and you crash , then your insurance is unlikely to payout .

I’d suggest you speak to your insurance anyway as it’s a modification and as such you won’t be covered unless they know about it .( you usually declare the car is not modified when taking insurance) .

hammy:
There is also the safety issue , if your headlamps go out and you crash , then your insurance is unlikely to payout .

In this regard read the disclaimer at the very bottom of the datasheet.