Newbie needs help with designing automobile cornering light circuit.

Thread Starter

stryped

Joined Sep 17, 2023
41
I have a 2013 Silverado. I would like to add lights to the front that would come on when the turn signal comes on, not blink but stay on solid, then turn off when the turn signal is off. This is to help me see where I am turning at night. I once had a 90 Lincoln town car that had lights like this from the factory.
I need to figure out where to mount these lights, I am thinking the lower sides of the front bumper.
It might be nice if I could also turn them both on manually, when on back roads as well as have them work with turn signals.
I am relatively new with circuits but am interested in learning.
Thanks for any help you can provide!
 

Externet

Joined Nov 29, 2005
2,182
My 62 Cadillac has cornering lamps. Tap the line that the turn signal lever ( --./.-- ) sends +12V to the flasher (node T). To avoid too much current trough the signal lever switch, a relay can be added, its coil to points T and GND. Normally open relay contacts to +12V and to the added sidelamp.

+12V-----------------------./.---------------------T--------------------flasher-----------------------turnbulb---------------------GND


1699749455720.png
1699749795440.png
(Above bumper end)
 
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MisterBill2

Joined Jan 23, 2018
17,814
The trigger can come from the turn signal feed, and use a timer to keep them on during the flash "off" segment. That is about as simple as can be,
 

Thread Starter

stryped

Joined Sep 17, 2023
41
The trigger can come from the turn signal feed, and use a timer to keep them on during the flash "off" segment. That is about as simple as can be,
Thanks.
If I wanted to also have the capability to turn both lights on with a switch regardless if the blinker is on or not how would I do that ?
 

LowQCab

Joined Nov 6, 2012
3,939
What You want to accomplish depends heavily on exactly how the Factory Wiring was designed.
You need to start with providing an Electrical-Schematic-Diagram for your particular vehicle.
They are NOT all the same like it was back in the ~60's.

When using a Timer, the "turn-off-time" will depend on how close You set the Timer to the
"Off-Time" of the Flasher-Module.
It can't be perfect, but it can be very close to "instant".

I think You may be asking for much more than You realize.
.
.
.
 

MisterBill2

Joined Jan 23, 2018
17,814
NOTHING in a car controlled by computer modules is instant, it is just "fast" in most cases.
Anything close to instant will need access to the actual switching contacts or sensor and be a very big deal to create and install.
LQC is correct !
 

MisterBill2

Joined Jan 23, 2018
17,814
In at least one recent vehicle I have driven, the turn signal was only triggered by the TS switch momentary action.
So really, the only simple access to a turn signal voltage will be the drive to the front turn signal light. And usually the external signal lights all use the vehicle frame ground-return connection. So always the front signal light will be a positive voltage.
And also, LQCab is rather understating the magnitude of the complexity of getting into the wiring of a current production vehicle.
 

MisterBill2

Joined Jan 23, 2018
17,814
OK, I see the switch and there is more information: It is a momentary closure , the TS switch just starts the signaling, it is not clear what stops it. I actually drove one of those STUPID vehicles and my evaluation of the turn signal scheme is that IT IS JUNK!!!
No simple way for the uninformed to cancel the TS flashing after a small lane change.
So my suggestion to take the trigger signal from the front TS light still holds. But only use it as a voltage level trigger because the light circuits are monitored to detect faults and failures.
The days of simple vehicle modifications are gone, as are the days of simple vehicle servicing.
 

geekoftheweek

Joined Oct 6, 2013
1,183
What part of the diagram signifies it is a momentary switch? I do know they have a feature where if you only bump the switch it will flash for a few moments and stop (not sure what year it started). I have driven four such vehicles (service trucks for work) and other than that addition all the turn signals worked flawlessly.

Edit...

I should also add that the switches still mechanically lock in place and are released when the steering wheel turns the opposite way unlocking the lever as has been done since the beginning on those trucks.
 
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geekoftheweek

Joined Oct 6, 2013
1,183
Like so if this schematic is accurate. Terminal 86 of the relay connects to the blue square on the wiring diagram.
View attachment 307437
I would not connect any relays to the BCM wiring directly. It is very well possible it is a 5 Volt signal and connecting a 12 Volt relay may cause more damage than you want to deal with.

Personally with newer stuff I would use a tap in the power from the turn signal bulb itself to drive a transistor of some variety (NPN or NFET) that would in turn perform low side switching of a relay coil. That would almost guarantee to issues with current sensing.
 

geekoftheweek

Joined Oct 6, 2013
1,183
In the event of a momentary switch starting the turn signal process as mentioned it would be nothing for the BCM to monitor the steering angle sensor and cancel the signal after a set amount of time at a defined steering wheel position. In other words it senses you are going fairly straight again for a few seconds and it cancels the signal.
 

MisterBill2

Joined Jan 23, 2018
17,814
What part of the diagram signifies it is a momentary switch? I do know they have a feature where if you only bump the switch it will flash for a few moments and stop (not sure what year it started). I have driven four such vehicles (service trucks for work) and other than that addition all the turn signals worked flawlessly.

Edit...

I should also add that the switches still mechanically lock in place and are released when the steering wheel turns the opposite way unlocking the lever as has been done since the beginning on those trucks.
OK, in the one I drove just a few miles, about three months ago, the turn signal lever never latched in either direction, it always returned to the center position. IN the circuit shown, the two turn signal switches did pull the connection down to the negative side (ground). Si for that system it is obvious that the lever switch sends a command to the body control computer.. That means that nothing else should be connected to that circuit. THAT is why I suggested triggering off the TS light feed circuit. THAT circuit is positive-going and higher powered, making it safer to connect to.
 

geekoftheweek

Joined Oct 6, 2013
1,183
I can't speak for anything new, but I can see a million different ways a momentary switch could be a good idea... and also a bad idea depending on how you look at it.

I'll venture a guess that the turn signal switch circuits in this case are simply active low signals much like the reset circuit of many microcontrollers and nothing overly complicated. A simple inverting comparator would probably be enough to pull a signal from the turn signal switch wiring.

I do agree 100% connecting anything to a BCM or any module is generally not a good idea these days without adequate understanding of what you're connecting to. Even then you are better off if you can find another way of going about doing it.
 

Thread Starter

stryped

Joined Sep 17, 2023
41
OK, in the one I drove just a few miles, about three months ago, the turn signal lever never latched in either direction, it always returned to the center position. IN the circuit shown, the two turn signal switches did pull the connection down to the negative side (ground). Si for that system it is obvious that the lever switch sends a command to the body control computer.. That means that nothing else should be connected to that circuit. THAT is why I suggested triggering off the TS light feed circuit. THAT circuit is positive-going and higher powered, making it safer to connect to.
Can I use the signal from the turn signal switch to the back to trigger the relay?
 
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