Skip Wolfe

The good news is I got the racecar started, the bad news is the car doesn't turn off when I hit turn off the ignition switch or the battery cutoff. As most know, there isn't any stock wiring in the car and is just a compination of the TEC3 harness, Painless Racercar 8 circuit harness, Stack harness, and customs wiring. I am using one of the solenoid battery cut-offs http://www.batterycutoff.com/ as well as toggle switches for ignition, starter, fuel, etc. Both the ignition toggle switch and batt cut off work fine without the car running (turns on/off dash, TEC3, aux gauges, etc), but when the car is running, I turn off the ignition switch and nothing happens - event the little red light in the ignition switch itself stays on. I am assuming the alternator is powering the system somehow,

Battery is hooked up to one side of cutoff switch (cut-off switch has alt
Other side of cutoff is hooked to:
- starter and alternator
- Red 10 awg wire on TEC3 Power Harness
- B+ of painless wiring harness to power relays for starter, fuel pump, fans, etc.
- to the ignition switch

The ignition switch then feeds:
- Stack dash
- gauges
- switches to activate the relays that control the fuel, fans, etc.
- the switched power for the Tec3 - yellow 18 awg wire on TEC3 Power Harness
- exciter wire on the alternator

Any thoughts on where I should start looking?

Geoffrey

Your issue is at the battery cutoff switch. You need to wire it properly and include and alternator to ground through a ballast resistor on the terminals that are closed when the switch is off. On the other terminals which are open when the switch is off, send it to a main relay or coil or ECU.

Here is an example of a wire harness although it does not show the battery cutoff wiring of the 4 posts on it.

Skip Wolfe

Thanks Geoffrey. I am using the aux terminals on the cut-off switch to send the alternator to ground through a ballast resistor (see schematic below), however I am not using the second set of switches. Should I use those to interupt power to the TEC3 ECU? Also this wouldn't help with the fact that the ignition switch also does not turn anything off would it? I hate automotive wiring - makes my head hurt.

Larry Herman

An alternative is to cut the fuel pump. Works like a charm on EFI motors and much easier to figure out.

Geoffrey

Naa, I would not cut the fuel pump as it would not immediately shut off the engine. You need to cut either the ignition system or the ECU (or both) on an EFI car.

Larry Herman

Geoffrey are you certain? I have seen it and done it this way, and the motor stops instantly.

Geoffrey

Yes, I'm certain. When the fuel pump shuts off, the fuel pressure diminishes over a few seconds. Since the ignition system and the ECU are still on, the engine will run until the fuel pressure is near zero and the engine runs to lean shutdown.

If you've wired it to the fuel pump relay on a Motronics car, it is likely that the relay also ran the Motronic DME and that is why th engine shut off immediately.

Skip Wolfe

Geoffrey is correct. I have the fuel pump on a seperate switch and have been using that to shut down the car while I troubleshoot this. It takes 4-5 seconds before it stumbles and shuts down.

Larry Herman

Thanks Geoffrey. It was on a Motronics car and so that explains it.

Skip Wolfe

Where should the alternator exciter wire connect? Right now I have it connected into the switched power bus, but I am thinking this is not correct and that the alternator continues to power the switched power bus (an concequently the ECU, switches for the fuel pump relay, etc.) through this wire. When the ingition/cut-off switches are still on, I can disconnect the exciter wire after the car is started and it stays running. However, when I turn the ingition/cut-off switches off, and the engine stays running, I then disconnect the exciter wire and the engine shuts-off instantly.

So the exciter wire seems to be the culprit, but I am not sure where to hook it up - battery 12+? the starter switch so it only gets power when starting?

Geoffrey

The way the alternator excite wire works is that when the engine is not running, the wire has continuity with ground. When the alternator is spinning it will show +12v on the excite wire. So, you need to wire up an alternator light on the dash where one side is +12v and the other side is connected to the alternator excite wire. When the engine is off, the light will be on and it will draw some current (I have to look back in my notes to see how much). When you start the engine, this load will trigger the alternator to begin charging and will send +12v on the line and the light will go out because there is no voltage differential on the bulb, you have +12v from battery and +12v from the alternator excite wire. You can use an LED, however, you need to wire a large 3-5w 250ohm resistor to draw enough current to excite the alternator. The good news is once you rev the engine past about 2500, the alternator will automatically kick on and begin charging. That is how it works.

The excite wire is also used to tell various electrical components that the engine is running, ABS Control units for instance have Terminal 61 (alternator excite) connected to them so they know when the engine is running. Some motorsport ECUs like MoTeC can use the alternator excite wire as an input and provide a separate output to a Racing alternator to turn it on and off under various condidions (full throttle for instance) to help reduce the drag and loss of power on the engine.

Due to the way you have it wired, the alternator field is still active when you turn the car off and it is powering your car. You need to also run the alternator excite wire to the battery cutoff switch through the terminals that are closed when the switch is off and through the ballast resistor to ground. This will allow the engine to shut off when the master is thrown.

Thats it! Don't connect the excite wire to any of the battery 12v+ circuit or it will continue to run as it does now.

Skip Wolfe

Thanks Geoffrey - I appreciate your patience. I was doing some research and found Painless recommends installing a diode inline with the exciter wire to prevent it from powering the car. Any thoughts? Would this be an alternative to the light or should I go with the light? The diode makes sense in that it wouldn't let 12v+ feeding back from the alterator to the switched 12v+ in the car. Will the light prevent the alternator field from still being active when I turn the car off and powering the car?

Geoffrey

The excite wire should not be installed to the 12v circuit of the car. Wire the light up which will also alert you to a broken fan belt and you know what that can do to an air cooled engine...

Once you disconnect the excite wire from the 12v circuit, you won't have any more issues.

Skip Wolfe

Geoffrey - you're the man! Installed the light on the exciter wire and it works perfectly. I still don't understand exactly how that makes a difference, but I happy to be able to move onto the other 100 items I need to troubleshoot.