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Discussion Starter · #1 · (Edited)
I'm hoping someone has seen this and can point me to the next step. This is a twist on a problem I've read on both Chevelle and Camaro forums.

1969 Chevelle Malibu Convertible with a 383, 400THD and an MSD 8362 ignition. Engine mods by the previous owner. Step by step I am fixing the errors.

In cold weather, the choke would come back on. The Edelbrock 1406 carb has an electric choke, so I started there. Found the power to it was 9.5 Volts. Discovered the source to be a tap off the MSD power supply. Yes, you guessed it, the power supply was the OEM resistance wire straight from the bulkhead connector. In this condition, the car would start and often run rich (smell), but it seemed to run OK. In the dark, with your foot in it, you might even get a flame to appear in the exhaust. Clearly, I needed to separate the power supplies and the ignition needed a pure 12V source.

I installed a relay board with 4 relays. I replaced the resistance wire with a 14 Ga wire to the relay board to simply be a trigger signal (ignition on, relays on). The relays source power is directly from the battery. When triggered, I get independent power to the MSD ignition, the choke and a fan for extra cooling. One spare relay. Looks and works beautifully, BUT............

Without starting the engine, If I turn the key to IGN, the relays turn on. If I then turn the key OFF, the relays turn OFF. All functions as expected. BUT, if I start the engine, turn the key to OFF does nothing. This points to back feeding from the alternator, at least that's what the posts lead me to believe. I did the test of unplugging the 2-wire plug ("F" and "R") from the alternator, shuts down perfectly.

The alternator is the original type: Delco Remy Series 10 with BAT, GND and a plug with an "F" (Field) and "R" (Relay) connection.
The voltage regulator is the original: Four wire - "F", 2 (same as "R" on the alternator) and 3,4 from the IGN switch.

Using the service manual, I checked the alternator positive and negative diodes and the field coil with my multimeter. Diodes checked OK, but the field resistance was 47 Ohms, so I suspected a problem. Pulled the alternator and had it bench tested. Results = GOOD. Reinstalled it.

There are lots of posts talking about back feeding the IGN circuit from the alternator once the engine starts. Unplugging the 2-wire plug ("F" and "R") would affirm that. The solutions posted vary from installing a diode external to the alternator to checking the IGN switch alignment to pulling fuses one-by-one until the engine stops.

The external diode idea seemed straight forward. I installed a diode on the "R" connection from a drawing I found on one of the posts. The engine shuts down OK, but because the relay coil no longer functions, the generator light on the dash stays on after the engine starts. The drawing was for the SI type (internally regulated). I only re-validated the unplug the F&R plug test.

I suspect this problem, whatever it is, existed before I installed the relays to fix the power supply to the MSD and Choke. The backfeed may not have been enough to keep the MSD firing, so the engine would shut down. By using the IGN feed as a trigger, the backfeed may certainly be enough.

I haven't been willing to drive "Lucille" until I get this resolved. I want to confirm timing and carburetor set-up now that I have full fire!!!

Any advice is appreciated.
 

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The proper install point for the diode is the #4 wire to the voltage regulator. This is the brown wire at the external regulator's connector.

Cut the brown wire and insert the diode in between the cut wire pieces. The little grey band on the diode needs to face towards the regulator side of the wire.
 

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Discussion Starter · #3 ·
Thanks Coppertop. In looking at the schematic, I understand the placement. My only question is what is the rating for the diode? I bought a 1N4001 (Radio Shack) rated for 50V, 1A continuous / 30A surge. Since the ratings are based on heat dissipation, I assume this is sufficient since once the engine starts, there should be essentially no current on the 4th wire. Would you agree?
 

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Discussion Starter · #4 ·
And so it continues. Diode installed on #4 wire (band toward the regulator) and the ignition functions properly (starts and stops OK), but the generator lamp remains on with the engine running. Service manual points to the field relay. Thoughts?
 

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Discussion Starter · #5 ·
I spoke too soon. I went to check the field voltage of the regulator per the service manual and I must have had a bad connection in connector to the regulator. I inserted my multi-meter probe, did the test and the generator light was off. Works fine now. The 1N4001 diode on #4 wire did the trick. Thanks again.

Here is a pic of my relay board installed.

Thanks again Coppertop.

On to the next problem.
 

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Discussion Starter · #8 ·
I don't see a pluggable one for the 1D alternator system. I only see diodes for the SI type.
 

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The plugs are the same.
No they aren't.

You provided a link to the SI style integrated regulator connector.

The original poster stated he had a 10DN externally regulated alternator. Different set-up, different plugs.

Need to get your facts straight.
 
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