S-Chassis Engine Start Button


We’ve wired up 2 of these now, one fully working, the other is on a non running car, so it’s hard to say, but they’re done exactly the same, so should be sweet.

Haven’t wired either car with the far right relay (3) yet, this one has been put in to safeguard the button from doing anything when the car is off. The ignition wire is only activated in the ‘on’ and ‘start’ positions of the ignition barrel. You only have to turn the key to ‘on’ for the button to work. When current is running through “Ignition” it activates the relay, which closes the circuit for the button, so that whole circuit works, otherwise the relay holds the circuit open.

For the button here we have used some street-fighter style illuminated temporary push-buttons, customised by Billy. All 3 relays are 30A SPST relays. I’ve labelled which terminal each wire connects to on standard relays too. Wires were simply spliced and junctioned into whichever was necessary, under the dash. We were able to buy relays that allowed to be set up as normally open and normally closed, you may have to specify that you need two ‘normally open’ relays and one normally closed. It may be worth fusing the 12v+ const with a 30A fuse too.

We also collected a number of spade connectors, small earthing ring terminals a couple of metres of speaker wire for the button and button illumination, and a couple of metres of red wire of a similar gauge to the wires we’re splicing into under the dash. All components should be able to be neatly tucked under the dash, and we placed the button in the cigarette lighter position, but could also go on the dash.

From the S13 workshop manual I found outline for which wires have power supplied at which positions. They are as follows:

off acc on start wires colour
1: – * * * 12v const: wht/red
2: – * * – acc: blue
3: – – * * ignition: blk/wht
4: – – – * starter motor: blk/yel
5: – – – * starter signal: blk/red

Since the key had to be turned to ‘on’ to disengage steering lock, we only had to make the changes from ‘on’ to suit ‘start’. This meant turning off accessories temporarily, and temporarily supplying power to starter motor and starter signal. The top relay (1) allows ‘accessories’ to run usually, until the start button is depressed, which opens the ‘accessories’ circuit. The lower relay (2) is usually open, until the button is pressed, which temporarily powers ‘starter motor’ and ‘starter signal’.

All black wires are earths. For illumination to the switch, a handy spot is the gearbox boot screws, and for the relays, there are plenty of spots you can screw the terminals to bare metal under the dash. For illumination of the light, we are currently getting 12v from the accessories line which runs into the stereo (also called 12v switching) which is on whenever accessories are on, meaning light is illuminated while driving. Ideally we will try to run it off something like the ‘check engine’ light on the dash, which will turn on in the ‘on’ position, then turn off when the car is running.

Will throw pics and video up some time soon.



About hitandrundc

Group of drifters based on the Northern Beaches of Sydney, Australia.
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