This article was first published in 2004.
|
Over the last few weeks in this series we’ve shown you the differences
between stability and traction control systems, and how you can turn off one
(traction control) without turning off the other (stability control). We’ve also
covered the use of three relays to allow you to have switchable on/ff traction
control while still retaining ABS and stability control functions. (If you’re
just joining us now, start at Part 1 – Modifying Electronic Car Handling Systems, Part 1
- otherwise it’s likely you’ll
soon be completely lost.)
This week, in the last of the series, we’ll show step-by-step how to build
the relay board and connect it up. The cost is low and while the wiring is a
little fiddly, it’s just a case of taking it slowly and carefully.
The Parts
As covered last week, the switchover system uses three relays. The Changeover
Relays need to be Double Pole Double Throw (DPDT) 12V designs, while the
Switching Relay can be a Single Pole Single Throw (SPST) 12V design. At the risk
of confusing you, you can also make the Switching Relay a DPDT design (and then
use only half of the contacts) – using all-DPDT designs makes it easier to
source the relays. You just buy three that are the same.
In addition to the three relays, you’ll also need some pre-punched circuit
board, terminal strips and a box. At the end of this story we’ve listed the
parts from Australia’s
Jaycar Electronics – if you live outside of
Australia you can
order them by mail order, or alternatively source much the same parts at any
electronics supply shop. None of the parts is anything unique or hard to
get.
Wiring the Relays
The key part of the system is making sure that the right relay contacts
connect to the right parts of the car. Easiest is to wire the relays on a small
pre-punched piece of board, mounting both the terminals and the relay on the
board. That way, you need only connect from the screw terminals to the car,
rather than trying to connect directly to the relay terminals themselves.
The pin-outs of DPDT relays varies, depending on brand. Shown here is the
approach taken with the Jaycar SY-4059 relays, which have a pin-out (viewed from underneath!) that looks
like this.
The connections that need to be made from the terminals to the relay pins are
shown here. The way in which you connect the pins to the terminal strips is up
to you, but we chose to use short lengths of insulated wire. That way, it’s easy
to arrange the wires without concern for short-circuits. That’s the upside; the
downside is that the end result looks is harder to follow in pics.
The first step is to connect the relay contacts to the terminal blocks.
The next step is to wire the coils of the two Changeover Relays through the
Common and Normally Closed contacts of the Switching Relay (black and red
wires). The brakelight input can also be added (white wire).
The connection for the traction control off warning light can then be made.
Note that this warning light isn’t obligatory but it makes sense that the driver
is alerted when the traction control system is off – none of the car’s OE
warning lights will show this.
Wired into place the relays and terminal strips should look like this. Note
that to make the soldering easier we glued the relays and terminal strips to the
board (using instant glue) before starting the underneath wiring.
Now that you’ve built the relay board it’s time to turn it over. This is what
the connections look like from
above.
|
Traction Control |
Pin Number |
Relay Function |
Left |
Left Rear ECU input positive |
1 |
Common |
Left Rear ECU input positive |
2 |
Common |
Left Rear Speed Sensor |
3 |
Normally Closed |
Left Rear Speed Sensor |
4 |
Normally Closed |
Left Front ECU Input positive |
5 |
Normally Open |
Left Front ECU Input negative |
6 |
Normally Open |
Right |
Right Rear ECU input positive |
7 |
Common |
Right Rear ECU input positive |
8 |
Common |
Right Rear Speed Sensor |
9 |
Normally Closed |
Right Rear Speed Sensor |
10 |
Normally Closed |
Right Front ECU Input positive |
11 |
Normally Open |
Left Front ECU Input negative |
12 |
Normally Open |
Here’s the system installed but before the wiring was tidied and the lid
placed on the box. Note the use of sticky labels on the wires – important if
you’re not to get lost in the wiring.
Conclusion
If you have a car with stability control and would like a bit more throttle
control over the way the car drives, this approach may be for you. It allows you
to easily switch the traction control on or off without affecting the stability
control or ABS and is a cheap and relatively straightforward modification.