[DeTomaso] Engine run after switching off ignition

[Thomas Tornblom]

JDeRyke at aol.com skrev:
> In a message dated 8/16/09 10:56:41 AM, Thomas.Tornblom at hax.se writes:
> 
>> I have finally gotten around to fix the run-after problem after 
>> installing the EDIS ignition.
>>
>> My schematic (1984 GT5) shows a resistor in parallel with the alt 
>> light, close to the speedo. In my car there is no resistor, the bulb 
>> acts as the resistor......
> 
> It gets worse. Our '72 L also had no resistor and the bulb not only is 
> the resistor, it's the ground termination for the alternator's field 
> circuit. If the field circuit opens, the next time the engine is run, 
> the alt will not charge!  As I found out when our bulb broke its 
> filament out. I curently own two perfectly good alternators and voltage 
> regulators.....

The bulb is not the ground termination, it provides the tiny amount of 
current needed to build enough magnetic field for the alternator to 
start charging. If you measure both sides of the filament when the 
engine is running you'll see that they are at +12V, so zero voltage over 
the bulb, and thus not lit.

On one of our trips to France the ring connector for the bulb circuit on 
the back of the Bosch alternator in my car broke off in flight. As the 
engine was running I didn't notice this as the alternator was charging 
properly and the lamp was obviously not lit.

After a stop over in Germany the alternator did not start charging, so 
the ammeter was far to the left.

Luckily someone in the group had a small assortment of press connectors 
and we were soon on our way again.


> Eons ago, my 250 Bultaco's Femsa magneto also used the tail Iight 
> filament as a system ground, so when the single cylinder dirt bike's 
> vibration broke its tail light bulb, the engine quit. Its been several 
> decades but I still remember that long walk home, pushing the thing. I 
> advise at least looking up there and if the resistor is not visible, add 
> one like Thomas did. Cheap insurance- J Deryke

I did not add a resistor, but it is probably a good idea to do that. I 
added one on an old golf we had that had a tiny charging lamp and it had 
to be revved to start charging. Adding a suitable resistor, say 
something between 50-100 ohms, 3 watts or higher, will probably work fine.

Thomas