Wiring up a turbo timer lesson 2

Yeah gang, I hear you asking: WTF happened to lesson 1. Well, Lesson one is wiring up a turbo timer for dummies. Hardly anything can go wrong when you have a decent harness, so I've skipped this lesson to go straight to lesson 2: Advanced wiring up of turbo timers.

Wiring up a turbo timer on an auto

Almost every turbo timer comes with a wire which must be connected to the parking brake. When this wire is pulled to ground, the turbo timer assumes you have the car in some kind of 'stand still' situation in which it is save to have the engine idle for a few moments. However, the position of the parking brake, does not tell a thing about the position the transmission is in. As it is almost impossible to detect the position of the transmission on a manual car, it is easy to do so on an automatic. 

The mkIV Supra (JZA-80) has a gear indicator on the dashboard. This indicator is signaled by the park / neutral switch on the automatic transmission. The signals are +12v; when the transmission is in park the 'green' wire will be +12v. When the transmission is in neutral the 'Blue' wire will be +12 v.

We can use the signals from the park / neutral position switch to add an extra safety to the turbo timer circuit. Use two general purpose diodes (1N4001) to connect the two signals to each other. We have to use diodes, otherwise the 'P' and 'N' lights will both illuminate when the transmission is in either 'P' or 'N'. The diodes must be connected together with the cathodes; the anodes are used for the two signals.

The 'output' signal, where the two cathodes come together must be fed to the coil of a simple relay. The other side of the coil must be connected to ground. Now when the transmission is in "P" or on "N", the relay will switch. You can use the switch side of the relay to interrupt the signal coming from the parking brake. This is an extra safety so your turbo timer will only be engaged when the transmission is in "P" or in "N" and the parking brake is on. If you don't want to use the parking brake, you can have the relay switch to a constant ground signal.

On the Mark 3 supra (MA-70) this technique is possible as well. On Pre-88 engines, the "P" signal is at B2, pin 10 and the "N" signal is at B1 pin 11. On Post-88 engines, the "P" signal is at B3, pin 7 and the "N" signal is at B2, pin 7.

Wiring up a turbo timer with an aftermarket alarm

Quite some cars these days come installed with an aftermarket alarm. A decent aftermarket alarm interrupts the starter and one additional signal which is needed for the engine to run. For example the fuel pump, the power to the injection or the EFI main relay. As an input the alarm uses the 'ON' signal of the ignition switch (the switch where you put your key in). When the ignition switch is in the 'ON' position, the alarm knows that it cannot be engaged as the car is obviously running. In case the car is not running and the start interruption circuit is engaged, you can disarm the alarm by putting the key in the 'on' position and press the alarm button. This whole system is signaled by this one signal coming from the 'on' wire from the ignition switch.

Problems with turbo timers

The main problem with a turbo timer in combination with an aftermarket alarm is you cannot arm the alarm when the engine is running on the turbo timer. To solve this, we have to tell the alarm somehow that the engine is running on the turbo timer, so it's 'safe' enough to arm the alarm. I've figured out various ways of doing this, depending on your configuration one is best suitable.

The best option to overcome this problem is to make use of the 'unlock warning switch'. This switch is located in your ignition switch and signals a wire to ground when the key is still in the ignition cylinder. You can use a relay with one side of the coil connected to a constant +12 volt and the other side to this signal (as in the JZA80 picture on the left, the yellow wire). The relay will be engaged when the key is in the cylinder and the relay will fall off when the key is removed. The switch of the relay can now be used to interrupt the +12 volt from the 'on' position to feed the aftermarket alarm. Only when the car is 'on' AND a key is in the cylinder, the alarm cannot be engaged.  All Supras have this unlock warning switch, but in some countries this switch is not wired up. The wires are hanging loose, so you can use the switch directly to interrupt the 'on' signal, without making use of a relay. Make sure you don't shorten the signal, so double check if the switch does not connect to ground anyhow. If this is the case, just feed the 'on' signal (+12v) to the unlock warning switch and use the other side of the unlock warning switch as a signal to the aftermarket alarm. You can cut off the wires from the unlock warning switch on USA spec supras as well, this gives you the removing of the irritating 'bling bling' when you have forgotten to take out your key while opening the door for free!

Although I cannot think of any car right now not equipped with the unlock warning switch, here is a solution in case you cannot make use of the previous option. The signal to the alarm must be +12 volt when the car is running or starting. This solution requires to cut the 'Acc' wire from the turbo timer. That's not a real problem, as the accessories in your car don't need cooling down time; the turbo timer is for cooling down the engine. When you've cut the 'Acc' line, connect the 'Acc' signal AND the 'Start' signal with two general purpose diodes (1N4001) together. We have to make use of diodes, so the signals don't interfere each other. If you don't use diodes, the starter will keep on running as soon as you put the key in the 'Acc' position!!! Putting the two signals together will create a signal which is '+12v' when the key is in the 'Acc', the 'On' or the 'Start' position. Whenever the car is running on the turbo timer, the signal won't be '+12v', as the turbo timer is disconnected from the 'Acc' wire!! In case your aftermarket alarm does not accept the glitches in the signal when switching from 'On' to 'Start', use a capacitor to freshen up the signal (2.2 uF). A resistor of 10 MOhm can be used as a load to the capacitor, so it doesn't take a lifetime to drop back to 0 volt.

What about circuit interruption?

I told you before, any decent aftermarket alarm interrupts at least two signals, of which one is the 'start' signal. You don't have to tamper with this signal when the car is running on the turbo timer, as it's obvious the signal is not needed (you don't need to 'start' a car that's running on a turbo timer).

The second interrupt of an aftermarket alarm can be connected to any other 'important' signal. In most cars the 'EFI main relay coil' is used for interruption. This signal comes from the computer and engages the EFI main relay. In the JZA80 this wire is green (see picture). The other side of the EFI main relay coil is connected to ground.

As soon as the alarm gets engaged, it disarms the starter signal AND this extra signal, in our case the EFI main relay. This would lead in the engine to stall, which is not what we want, as we would like to have the engine idle for a few moments on the turbo timer. To overcome this problem, we need to feed the EFI main relay an extra power supply, telling 'hey keep on going for a while until we really shutoff'. This signal can be obtained from the fuel pump. Feed the power that's going to the fuel pump using one general purpose diode (1N4001) to the coil of the EFI main relay. Now when the ECU signals the relay to close, the diode will block this signal and prevent it from going to the fuel pump. When the car is running, the EFI main relay is kept closed by either the signal of the computer (no inline diode needed), or the fuel pump signal, but hey this is the same.

When the alarm gets engaged, the signal from the ECU will be interrupted by the alarm, but as long as the engine is idling on the turbo timer, the EFI main relay will be kept closed by the signal for the fuel pump, preventing the car from shutting off!! When the turbo timer comes to it's final countdown, the power will fall off and so will the EFI main relay. The car is now 'double blocked'. Pretty neat solution, right?