engine and drivetrain Basic Ignition Principals Please

[devo1]

Allow me to share my ignorance in all things electrical.

The engine starts when the key is rotated to the start position but dies when it is released and returns to the run position. New ignition switch. All functions operate as normal in the run position except no battery charge warning light (and the engine doesn't run). Wiring is all correct and connections good. Fuel and carbs good. The timing and plugs work since the engine catches and runs as long as the starter is engaged but that is going to ruin the starter if I keep it turning. Alternator???

As far as I can tell from the schematic, the coil is feed from the starter solenoid and the alternator feeds the battery - right? The alternator doesn't connect to the ignition system -coil, plugs, dizzy.

Can the engine not run just from the battery until it goes flat? If so, then why does the engine die when the key returns to run?

Assuming the alternator has to be working in order for the engine to run, how do I test the alternator as a source of the problem? How do I test it with the engine not running.

I'm way better with a wrench.

Doug

[Mike Self]

Your ign feed is somehow disconnecting when the ign switch is in the run (On) position...the following presumes you have a standard ign system--no Pertronix, no Crane or other aftermarket ign components, just a plain ole coil, points and battery.

1. You have a wire mis-connected at the ign switch. The fact that the alt warning light doesn't illuminate when the ign switch is in the run position is a clue (is that bulb burned out?)

2. The resistor at the coil that changes coil voltage when the key is in the start position is malfunctioning and cutting voltage to the coil, and/or the ignition relay (mounted on the firewall near the dizzy) isn't functioning.

Try connecting a voltmeter to the + terminal on the coil (other voltmeter wire to ground) and observe the voltage as you go from the On switch position to Start and back to On. If the voltmeter reads 0 in the On position, that's your problem.

Let us know what you found.

mike

[wagnerf15]

The wire from the starter to the coil is the one that steps up voltage during start (bypasses the resistor) and not the primary 12v feed for the coil. Again assuming you have the stock set-up, you'll have to find the other 12v wire that hooks to the coil. It makes sense in that while you have the starter engaged, the coil sees 12v and it dies when you release the starter. Any spare wires hanging around the coil?

[devo1]

Firstly this is on the 73 CS. It is not a stock ignition but everything the PO did before I bought the car worked well and has never given me any problems. I'll dig up a full description with a couple of photos but basics are a bosch mechanical distributor and 1982 528i ignition module.

There is a VDO ammeter correctly wired as per the instruction sheet so the red wire from the alternator goes to the ammeter and then to the ignition switch. A 10ga wire goes from the second pole of the ammeter to the starter post that is fed from the battery and that is the charging loop. I'll try all your suggestions this weekend. There is no ignition rely and none shown on the 73 schematic diagram.

Everything worked this fall when I put the car to bed for winter during which I re-cored the heater, removed the derelict A/C blower and associated wiring and rebuilt the console.

Doug

[Napes]

OT for Mike S.

You mentioned: the ignition relay (mounted on the firewall near the dizzy) isn't functioning.

I just looked @ my ' 75 and there's no relay on the firewall anywhere near the dizzy, or, for that matter, none 'til you get clear over to the driver's side of the car. Was the iginition relay on the square-lites relocated?

Thanks,

Bob Napier