Security Lamp Circuit Mod
© 2004 Chops101
What is this mod?
This is an add-on circuit to your existing security circuit. This mod will carry the 'presence' of your PATS security circuit outside of your truck. LED's are placed in both L&R front "turn signal corner assemblies" and in the rear L&R clear "reverse" area of the light housing assemblies.
What does this accomplish?
This mod does not offer any additional real protection, it IS NOT an alarm, it will not keep your Trac from being vandalized. What it may do is infer to a would-be criminal, "There's some kind of expensive, bizarre security system attached to this truck that I've never seen before. I think I'll pass to an easier target."
How does it work?
High intensity LED's will "blip" in sequence with the OEM security lamp in the dash. An optional, switched piezo element will "chirp" in sequence additionally, under the hood. You get the visual and audible indication that there is something different associated with this truck; leave it alone.
Will this run down my battery?
No. Four High Intensity LED's @ 30mA each, the piezo element @ 5mA, Total current is 125mA. Remember this is a "pulse" of about 250ms, not continuously active. I have a similar setup like this on my Harley, (single LED, piezo element) tied into the alarm circuit, and have left it alone weeks at a time. Of course a motorcycle battery is multiple times smaller in capacity.
On with the project
I chose blue LED's at 6000mcd, because they are unique. Any color will do, there is absolutely no flashing happening while the engine is running. The magnification factor of the rear reverse lens really is bright!
I also wired mine in such a way that I can have :
1. Four LED's blipping and no audible chirp.
2. Four LED's blipping and an audible chirp under the hood : 86dB @ 3500 Hz.
3. Mod Off- Only the factory panel security lamp is active.
First, remove the four light assembles (removal procedures covered in other projects, but it takes about ten seconds to figure this out)
Drill holes near the bulbs to mount the LED's. LED snap in holders are available at Radio Shack, but I epoxied mine in for more permanence and wire stability. I soldered light gauge speaker wire (50' roll) to each LED, bent the leads over, hot glue the ends (to keep in place) , and then epoxy over the LED and leads.
Wire the LED's in parallel. Along the way polarity has to be identified for each LED. There are no wire polarity markings on some of the smaller gauge wires available, be careful. Route the wires from the rear of the truck on the right side, on top of the chassis beam. Secure with nylon ties, and bring this up into the passenger side engine compartment, next to the fan motor. Route the front wires to this same fan motor area. Mount the piezo element by means of double-sided tape in a dry location under the hood.
And now the schematic
This should answer a lot of questions. Starting with the parts list:
LED D1-D4: (4) 6000mcd, 30ma, 3.6v Blue
D5: 1A power diode
SW1: SPDT, Center OFF, SubMini
R1: 330ohms, 1/2w
F1: .315 a (yes, POINT three-one-five, 315mA)
Piezo: 3500Hz, 86dB, 3-12v element
How this works: The OEM security light in the dash operates by 12v being applied to the LED anode constantly, the cathode is pulse gated low via the logic circuit at Pin 30 of the PCU.
A fused 12v constant source (I piggybacked on a fuse in the fuse panel) connects SW1 "2". Remember this is a center off switch. As switch is closed "position 2 and 1", power is applied to the four LED's, and is pulse gated low as the PCU allows, completing the circuit. D5 acts as a one way gate, power is not applied to the piezo in this position.
As switch is reversed and closed "position 2 and 3", power is applied to the piezo, and is pulse gated low as the PCU allows. Additionally, D5 conducts and power is applied to the LED's. To recap; switch position 2+1/ LED's only, position 2+3/piezo and LED's, center position, circuit mod off.
Again this draws very little current-125mA total, do not use a large fuse. If a LED shorts or a wire burns into, the small fuse will go and save potential damage to the PCU. R1 value may vary depending on I rating and V rating of LED's. A simple ohm's law formula to determine the value of R1:
R1= Vin - Vled / I led
Whereas Vin = 12.6 , Vled=3.6 , I led=.03, R1 would = 300 ohms, driving the LED's to max spec.
With a 330 ohm resistor, the LED's I chose are being driven with ~3v, well under spec.
Tap into Pin 30 very carefully inside the plastic shroud of the PCU connecter. Use quick disconnects and test the LED circuit (just touch the unconnected large green wire in the picture, that will mate to pin 30, to a ground temporarily).
That's pretty much it. It is a simple circuit, I keep it switched in the LED on only position and have left it there. I will use the piezo chirp at some point, it depends on where the truck is parked. The submini switch is mounted away from view high up on the side of the center console.
Any questions, shoot me an email: chops101@yahoo.com
Have Fun!
Chops 05/2004
This is a copyrighted document. Absolutely no portion of this project to be sold, bartered, or traded by any means at any price, retransmitted, copied, borrowed, reposted on any other website, or used in any way other than the original intent of knowledge sharing.
