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Stock Door Switch Circuit with Added Relay
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Overview
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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
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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.
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Lay Out Your Parts
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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).
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Assemble the Relay/Capacitor Circuit
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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.
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Attach Connectors To Relay Harness
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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.
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Disconnect Door Switch
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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.
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Tap Into Door Light Wire
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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.
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Verify You've Got the Correct Wire
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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.
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Temporarily Connect Relay and Test Circuit
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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.
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Wrap Up and Protect Circuit Parts
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Using Zip Ties, Electrical Tape, or whatever else you feel like
using, cover all bare wires (like capacitor leads) and secure all
connections.
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Find a Happy Home For Your Circuit
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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.
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