Reversion Diode

[aaronlwag]

I think I blew a reversion diode in my '81 Spider when (ahem) the battery was hooked up in reverse. When I now hook up the battery (correctly) the car is always on (even with the ignition switch unplugged). The car will start fine but will not shut off (I had to stall it). Please help me find the correct Diode to replace and if it isn't a diode in this car, what is it? I do have a wiring diagram but it is a bit unclear. I think it is off of the brown wire near the alternator but I am not sure.

Please help.

Aaron

[Ernie]

Aaron,

I've never seen it, but I've read somewhere a Spider that continues to run with ignition off is usually a symptom of the diodes in the alternator gone bad.

Ernie

[RoyBatty]

Reversion diode eh?

Are you sure it's not the flux capacitor?

[aaronlwag]

A reversion diode is like a one way valve that only allows current to flow in one direction. This is what prevents the car from turning on until the ignition switch is deployed...a flux capacitor allows a 1981 Delorean to travel through time at 88 miles per hour.

[divace73]

by their very nature all diodes are a one way device, unless on course there is the flux capicitor involved ....don't know how the Delorean would get to 88 mph with the original power plant, it wasn't much chop.

[RoyBatty]

So is the 88 mph the terminal speed at which the DeLorean travels thru time?
And if a reversion diode was placed in the circuit would it allow you to easily reverse the trip?

[aaronlwag]

Enough with time travel, does anyone know where this thing is in my car so I can replace it and get it to turn off?

[spider2081]

If you have an 81 with fuel injection I agree that the most possible shorted diode is internal to the alternator. Try disconnecting the small wire(black/violet) that pushes into the back of the alternator when the car is running and see if it stops running. If it does the alternator has at least one shorted diode and needs to be overhauled or replaced.
Let us know what you find

[RoyBatty]

It was always my understanding that an alternator with a bad diode in the cluster would not put out a proper charge.
As far as the car not stopping when you turn off or disconnect the ignition switch.
It sounds as though you may have shorted the coil primary wire to a power wire with the reversed battery situation.
For the engine to remain running, the coil primary wire is always getting power.

I am of course referring to the wire that carries the 12v power to the coil from the car body.

[mdrburchette]

I had this problem when I installed a MSD box and Blaster II coil. The extra current kept the system energized and wouldn't let the car shut off so I installed a diode in the field wire at the alternator and it fixed the problem.

[aaronlwag]

Is there any chance it could be the voltage regulator?

[mdrburchette]

The problem is the field wire is still getting juice, which causes the system to think it is still on. I don't know how the regulator could be in the loop....but I learn something new every day.

[aaronlwag]

According to the shop manual, the Voltage Regulator is integral to the Alternator. there are also rectifier diodes internal, perhaps that is what has blown? I would think that replacing the Alternator should fix the problem...what do you think?

[mdrburchette]

Will bench testing the alternator show what the problem is? I was thinking about the external regulated alternator.

[aaronlwag]

I removed the alternator today and noticed that the black wire appears to have sheared off at the terminal. I will hook it back up tomorrow and see if this is the problem. With the alternator removed, I hooked up the battery again and got no power to the radio so this may be a clue.