Ignition Start Pushbutton
From Taurus Car Club Maintenance and Modification Wiki
IGNITION START PUSHBUTTON
This modification of the start circuit adds Ferrari-style push-button to your car controls. I designed this system to parallel the key start. With the switch in OFF position the system is disconnected from the car wiring and the key operates the start. In ON position, the key START function is disabled and the push-button is used. Additional relays disconnect systems which are disabled when the key is in START position, so that the battery can deliver maximum current to the starter. A simple transistor switch activated by a 13V Zener diode controls relay R1, when the voltage goes above 13V, it removes the ground from the power relay R2. If the engine is running and the system generates the usual 14.3V or so, the push-button START is disabled.
Here is the view of the START and ON/OFF button - it is OFF
A basic knowledge of car electrics, how to crimp, splice, solder etc. is required. If you are not comfortable doing this work and if this would be your first project of this nature, think carefully before you decide to tackle it. You don’t want your car to stop in the middle of nowhere because instead of soldering, the wires were twisted and decided to part company.
The information here is for a 94 Sable with the Essex 3.8 engine. For other models you need to review the schematics of the circuits which you will need to hack into.
The system presented here was tested and is working in my car. However, I WILL NOT BE RESPONSIBLE if you blow fuses, burn wires or otherwise render either a part or the whole system inoperable.
Here is the electrical diagram
Tools:
Wire cutter, insulation stripper, crimping tool, soldering iron, drill, Dremel tool and assorted bits for panel cutout for the switches, screwdriver stc.
Parts:
1. Pushbutton, momentary, with NO (normally open) contacts and preferably illuminated with either a 12V bulb or a LED. Find one you like, with a nice action, not too light, you have to feel it while wearing gloves in winter. For diode light, make sure it has the necessary resistor, if not put around 680 ohm in series.
2. ON/OFF switch, double contacts
3. Four 12V automotive relays, R2, R3 ,R4, R5, they usually have built-in diodes, with these watch for coil polarity; for R1 any small relay will do, even a 5VDC can be used, with about 150 ohm resistor in series with the coil, suppressor diode will be necessary
4. Automotive fuse, 5A and fuse holder. NOTE: it blew on me once, since I replaced it with a 7.5A.
5. Transistor, NPN type like NTE123A/2N2222, or newer NTE123AP/PN2222, almost any transistor can be used, with Ic of 600-800mA.
6. Zener diode, 13V, NTE5022A
7. Diode, silicon, NTE519, 1N4148 or similar, this is a suppressor diode for the relay, if no internal diode is provided.
8. Resistors, one 1kOhm and one 10 kOhm, ¼ Watt is sufficient 9. Crimp connectors male/female, butt connectors, screw type terminal strip, electrical tape or shrink insulation, automotive wire 16-18 gauge, use same gauge as the wires you connect to, for switches and relay controls 20 ga is ok.
Plan your layout carefully; check if the switches fit where you want them to be. Don't drill and cut holes until there is nothing else to do. Disconnect the battery while working on wiring. Connecting wires requires crimping or soldering, some connections, especially those where you need to disconnect something quickly can be screw terminals. I always do tinning of the wire, both for crimping and screw terminal.
Picture of an assortment of parts (switch at the top: I used a different one, a pushbutton, did not want to pull it out for the photo shooting...)
Step 1.
Get to the wire which is energized in RUN and START, in my case it was no. 16, Red/Light Green wire. It can be accessed on the left side of the steering column, opposite ignition switch. You need to tap power from this wire. Either cut the wire and connect a length of wire by soldering and/or crimping all three together or cut the insulation and solder this feed insulating the connection with electrical tape and maybe put a tie or two for safety. In my case, I soldered a 3/16 inch wide by 1-1/4 strip of .030 copper to the end of the wire and inserted it into the ignition switch connector box where the R/LG wire is plugged. This box is closed with a snap cover but can be opened easily. Usually there is enough room for this insert, this worked for me on a couple of occasions, wire cutting wire and manipulating of soldering iron in tight quarters can be avoided this way. Once you have the feed attached, run it to the terminal strip and secure. Connect the fuse holder lead to the same terminal; attach the other end to another terminal. This is your power point. You will connect more wires to it. To get power to the next terminal in the strip, use a short U shaped jumper. Get enough length on the fuse wires so that you can pull it from underneath the cover if fuse needs replacing.
View of the wiring
... and the fuse
Step 2.
Locate START wire, it will in the same area as the previous one. On my 94 it was no. 33, White/Pink. Here you need to cut it in an accessible spot and attach two lengths of same gauge, it was 16 I think, using butt connectors. Mark the wires so that you know which is coming from the ignition switch and which goes to the START. Crimp insulated female connectors to both ends and if you have your relay ready, connect upstream wire or the one going TO the ignition switch to terminal 87a, the other, downstream wire to the terminal 30. Those terminals are NC, Normally Closed, so your original wiring path is the same.
Step 3.
Locate the wires which are switched off in key START position. Mine were No. 287 and 687. I modified the 297, the other does not appear to carry any significant load, it has ABS module on it which I don’t have. 297 however, has a total of 50A of fuses downstream, so it was logical to switch it off for starting. Select your wires, cut, install connectors and connect relays as per the diagram.
Step 4.
Wire ON/OFF switch, pushbutton and indicator light. Solder, screw or crimp quick connectors depending on the terminals you have on the switches. The length of wires depends on the location of your switches and the overall layout. Longer wires can be bundled and tucked away.
Step 5.
Overvoltage switch. It is best to use circuit board but perforated board will work as well. I made a small circuit board integrated with two relays, etching the board, soldering and enclosing it in a small aluminum box, just for fun and more work…Because of the simplicity of the circuit, I can imagine it can be made with a piece of cardboard, piercing holes, sticking the few components in and soldering the legs. Watch the orientation of the transistor and Zener. There is tons of relevant info on the web on this subject. The collector is the output and it connects to the negative leg of coil of R1, A to A, see the diagram. To test the switch before it is connected to the system, power it from the power point (fused terminal), connect ground as shown and connect a low watt (5-6W) test light like this: one lead to point A, the other to your power point. Now turn the key to Run, check the light, it should be off. Start the car, check the light, it should be on.
This shows the overvoltage module attached to the cross brace, it is the ground, too
Step 6.
Install START and ON/OFF switch where it will be easy to operate them. I found the place in the top corner of the lower cover to be perfect for me: I can see the button through the steering wheel and it is easy reach. I machined the shape for the switches out of solid aluminum and fitted it to the curvature of the cover. A flat faceplate attached to the cover will be much easier to make and, painted to match the dashboard, should look good.
Another look, now the system is ON
I enjoy using this mod very much.
Stan
