1995 3000GT VR-4: Enabling Headlight Auto-Shutoff With a Turbo Timer

These instructions apply to a 1995 Mitsubishi 3000GT VR-4, but are easily transferable to any model/year of 3000GT or Dodge Stealth.

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Circuit Schematic

Stock Door Switch Circuit with Added Relay
  • This schematic shows the stock door switch circuit (white background) and some additional components (blue background) that allow the circuit to shut off the headlights when the Turbo Timer shuts off the car. In this particular circuit, the added components are: a SPST relay and a 2200uF capacitor.

    Here's what the circuit looks like when connected to the turbo timer circuit:

Circuit Functional Description
  • When the relay is on (energized), pins 30 and 87 are connected, which connects the OEM yellow door switch wire to ground. This makes it "look" like the door is open. The relay is on whenever 12V is applied to terminal 85, which in this case, is whenever the turbo timer is applying power to the ACC wire. My turbo timer (Blitz DTT-X) only powers the ACC wire (blue) when it is actually running the car (key out of ignition). If there were no capacitor, this circuit would make the door "look" open while the turbo timer is running the car, but as soon as the timer turned off, the door would "look" closed, and the headlights would stay on. That's where the capacitor does its job - the capacitor stores energy whenever the TT ACC wire is powered, and then when power is disconnected from the ACC wire, the capacitor provides current to keep the relay coil (terminal 85) powered for a certain amount of time. How much time is based on the size of the capacitor and the resistance of the relay coil. For my particular relay and capacitor, the time the relay stays on (making the door "look" open) is about 0.25sec. That's really small, but it's all the OEM auto shut-off circuit needs to sense that the door was "opened" after the ignition is off.

The Procedure

Lay Out Your Parts
  Here you see the relay, the relay harness, and the capacitor. If you have a SPDT relay harness, now would be the time to pull the center wire out of it if you like. I pulled it out (the black wire at the top).


Assemble the Relay/Capacitor Circuit
  Connect the anode (negative) side of the capacitor to the brown wire using some kind of secure connection. As you can see, I used a small length of 18ga wire, quick-disconnect fittings, and a T-tap on each side of the capacitor. Connect the cathode (positive) side of the capacitor the same way, but to the blue wire. I also wrapped the ends of the capacitor with electrical tape, just to make sure nothing will ground out against the chassis.


Attach Connectors To Relay Harness
  Now you need to attach some connectors to the relay harness - the yellow and brown wires need to be grounded, so I crimped them both into a ring terminal and attached the ring terminal to a grounding screw located near the driver's foot-light. Since I used a T-tap to access the OEM door light wire, I used a male quick-disconnect fitting on the red wire. In this picture, the blue wire has no connector on it, because I was still experimenting at the time. My final circuit used a pair of 14-16ga male/female quick disconnect fittings for this blue wire and the blue wire on the Turbo-Timer harness.


Disconnect Door Switch
  The door switch is attached to the car by one Phillips screw. On the '91-'93 cars, you have to pull the rubber boot out of the way to access the screw. You may see some small sparks as you remove the switch from the chassis as there is a live connection powering the red light in the door. The sparks are common and harmless, so don't be shocked if you see them. :-) Disconnect the harness from the switch so you can access the wires for the switch.


Tap Into Door Light Wire
  Attach an 18ga T-Tap to the yellow wire found in the bundle of wires to the left of the clutch pedal. This was the only solid yellow wire I found in this bundle, but I didn't search exhaustively. That's the reason for the next step. You may be able to access this wire bundle without pulling out the trim pieces for the door sill, but I found it much easier with the trim removed. Also, the only way I was going to get a decent picture was with the trim pulled and the carpet pulled back.


Verify You've Got the Correct Wire
  To be sure you have tapped into the correct yellow wire near the driver's foot area, connect one end of your multimeter (ohm-meter, or continuity tester) to the T-Tap you just installed and connect the other end of the multimeter to the pin on the door switch harness that corresponds to the yellow wire. If you get 0.0 ohms (continuity), then you've found the correct wire.


Temporarily Connect Relay and Test Circuit
  To make sure the circuit will work in your car and that you have all the connections set up properly, connect the 4 circuit wires to your car and test that your headlights turn off when the Turbo Timer shuts down the car. As you can see from the picture and from the circuit diagram, the yellow and brown wires get grounded, the red wire goes to the door light wire (T-Tap), and the blue wire goes to the Turbo Timer's ACC output.


Wrap Up and Protect Circuit Parts
  Using Zip Ties, Electrical Tape, or whatever else you feel like using, cover all bare wires (like capacitor leads) and secure all connections.


Find a Happy Home For Your Circuit
  I tucked my circuit parts behind the plastic protector, near the flasher relay. Note that in the picture, the blue wire is unconnected as I was in the process of routing it up through the dash so that it wouldn't be in the way. It does, of course, need to be connected for the circuit to operate.


Alternate Circuit Schematic

Stock Door Switch Circuit with Added Transistor
  • Here's a quick example of another circuit that you could build to solve this problem. It uses a MOSFET instead of a relay, so it's more efficient and doesn't require a huge capacitor. I ended up not using this circuit because it required soldering and more careful protection of the transistor than the above relay/capacitor circuit. I did, however, build this circuit on a breadboard and it does work.
Circuit Functional Description
  • When the transistor is on , the drain and source terminals are connected, which connects the OEM yellow door switch wire to ground. This makes it "look" like the door is open. The transistor is on whenever 12V is applied to the gate terminal(Vgs > 4V), which in this case, is whenever the turbo timer is applying power to the ACC wire.

    If there were no resistor between the transistor's gate and ground, the circuit would never turn off the transistor due to the transistor's gate capacitance. This would make the door light stay on indefinitely and drain your battery. In theory, you could use a really big resistor and not have the external capacitor, but I chose to use the extra capacitor so that I could have a reliable RC time-constant for the circuit. The resistor and capacitor I chose will keep the door light on for about 6-8 seconds after the car shuts down. That's plenty of time for the auto-shutoff circuit to be tripped, and you could use a smaller capacitor and/or resistor, as long as your RC (resistor value multiplied by capacitor value) is 0.25 or higher.

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Last Modified Mon Oct 20 2003 17:32:38 PDT