Need help with a diode.

[richards72chevy]

I'm having a problem of my 66 turning over with key in the off position.I figured it may be my switch but further reading on here suggest I need a diode.I have covereted over to an internal regulated alternator a few years ago and never had this problem.I just put in a electric cooling fan and now have this problem.I definitely am going to put a diode on the alternator.Do I need a diode anywhere else? From what I have read on here the diode is a simple cheap fix but all the diodes I'm seeing on the auto zone website are about 50 dollars plus and they all look a little different.Does any one have a picture or a part number to the diode I need? Thanks.

[franken]

You should probably get a DVM and start troubleshooting the issue rather than looking for magic diodes.

[dmjlambert]

No problem with this alternator for years and now that you've added a fan the problem happens? That does sound odd. Perhaps you can show us a diagram of how you have things connected. Do you have a particular article you read about diodes you can give a link to? Where does it go? What does 66 turning over with key in the off position mean?

[richards72chevy]

Originally Posted by dmjlambert

No problem with this alternator for years and now that you've added a fan the problem happens? That does sound odd. Perhaps you can show us a diagram of how you have things connected. Do you have a particular article you read about diodes you can give a link to? Where does it go? What does 66 turning over with key in the off position mean?

Sorry I should have been more specific.When I turn the key off the engine stops running then in a few seconds after that the engine starts turning over.I have to get out of the truck and disconnect the battery cables.l am no electric genius by any means so bear with me.I never heard of a diode until I seen it on this website.

[VetteVet]

The next time you run the engine before you shut it down disconnect the fan power wire and then shut it off and see if the problem happens. I suspect you have wired something wrong in the power circuit. Try to give a few more details such as "the engine starts cranking" or "it runs with the key off" or how you wired the fan as has been asked.
Also disconnect the alternator and then try the engine run shut and see what happens.

The starter circuit is very simple on the 66 and all the other years for that matter. The power goes to the key switch and the key switch sends it on to the starter solenoid. I don't know for sure but I don't think some of them had neutral safety switches.

[richards72chevy]

This is how the fan is wired up except instead of having the wire go the ignition switch it's going to the fuse panel.Screenshot_20200831-125454.jpg

[richards72chevy]

Originally Posted by VetteVet

The next time you run the engine before you shut it down disconnect the fan power wire and then shut it off and see if the problem happens. I suspect you have wired something wrong in the power circuit. Try to give a few more details such as "the engine starts cranking" or "it runs with the key off" or how you wired the fan as has been asked.
Also disconnect the alternator and then try the engine run shut and see what happens.

The starter circuit is very simple on the 66 and all the other years for that matter. The power goes to the key switch and the key switch sends it on to the starter solenoid. I don't know for sure but I don't think some of them had neutral safety switches.

VetteVet I was looking through an old thread I started and I never did locate the wire for the warning light.Is this the wire that is supposed to go to a dash light for the charging system?The wire is is cut so I don't know where it's supposed to go.IMG_20200830_130848.jpg I'm pointing to the brown wire with my test light.

[VetteVet]

The brown wire you are pointing to goes to a fuse that is hidden by the pink wire. These fuse panels are slightly differently from year to year so I can't say for sure where the brown wire goes until I know what the fuse is. The 67/72 fuse panel is shown in the lower diagram.
What is the red wire on the fuse next to it? that looks like it may be the heater switch fuse.

The diagram below shows the route of the charging light and if you look at the center right you'll see the light, which they call the Gen tell tale light. It has a brown wire and a pink wire connected to it. The pink wire comes from the key switch via the pink ign wire to the fuse panel and then up to the three way junction by the Gen light. The brown wire from the light if you follow it, goes back through the forward firewall connection and out into the engine bay, and it ends at the external voltage regulator to terminal F . Depending on how they did the alternator conversion, They may have done away with it or they may have jumpered it to the white wire on the regulator.

If you look at the key switch on the top of the diagram you'll see a brown/white striped wire which goes down and joins the brown wire from the Gen light. This is a resistor wire about 10 ohms which equals the resistance of the Gen Tell Tale light. The alternator needs to see a resistance of 10 ohms from the brown wire to prevent the alternator diode from burning out and to prevent the engine from running on after you shut the key off.

This wire from the key switch is there in case the Gen light burns out, it will continue to protect the alternator and work as the exciter to start the alternator charging when the engine starts. The trucks without the charging
light "gauge dashes" still have this wire from the key switch.

[Andy4639]

It sounds like the fan is acting as a generator and back feeding to the ignition. This will cause the engine to try and start are Dieseling after you shut it off.
Reading up on it on these 2 links.


https://www.chevytalk.org/fusionbb/s...hp?tid/298183/

https://www.jalopyjournal.com/forum/...is-off.804152/