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Old 10-10-2020, 09:43 PM   #1
FLBLAZE
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Stock 250 CID / I6 Alternator wiring picture

I canít get my Ď72 Blazer started (250 CID I6) after removing the alternator (rookie mistake of assuming Iíd remember the wiring / not photographing the wiring prior to taking it apart). So, can anyone please send me a picture of the alternator wiring in your stock I6 250 CID engine. Many thanks in advance.
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Old 10-10-2020, 10:19 PM   #2
'68OrangeSunshine
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Re: Stock 250 CID / I6 Alternator wiring picture

There are only 3 connections. The Red lead goes on the positive terminal. This is the biggest one and is more outboard. Some alternators have a stud connection that's red inside, under a rubber ''hood.'' The field connector is a dual-lead plug that snaps in to the socket at 12'o'clock on the back of the case. The Ground stud is more inboard and connected by a smaller Black lead, sometimes there's a metal clamp crimped around the whole bundle with a tab that goes into a slot on the back of the Delcotron casing. It's secured by a smaller nut.
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Old 10-11-2020, 08:30 PM   #3
72c20customcamper
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Re: Stock 250 CID / I6 Alternator wiring picture

I'll get one of my 68 in the morning
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Old 10-11-2020, 08:46 PM   #4
FLBLAZE
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Re: Stock 250 CID / I6 Alternator wiring picture

Thanks Mark. I’m pretty sure I have the wiring correct but it still won’t start. It turns over but doesn’t engage.
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Old 10-11-2020, 09:01 PM   #5
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Re: Stock 250 CID / I6 Alternator wiring picture

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Originally Posted by FLBLAZE View Post
Thanks Mark. Iím pretty sure I have the wiring correct but it still wonít start. It turns over but doesnít engage.
Under normal circumstances, the simple act of replacing the alternator shouldn't cause a no start condition.. i suspect you have another problem.. Engine cranking over but not starting is not a symptom of a failed alternator.. Why was the alternator replaced??
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Old 10-11-2020, 09:38 PM   #6
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Re: Stock 250 CID / I6 Alternator wiring picture

You’re right RustyPile. The alternator was not technically replaced. I changed the belt and removed the alternator due to stripping the threads in the top / bracket position, only to find out from someone much smarter on this very forum, that all I had to do was replace the screw with a longer version and tighten it with a bolt. But by then I had already removed the wire connections to the alternator... �� All this to say that I’m confident it’s not the alternator. I’ve got a couple of ideas to try out based on what I did. So I appreciate your help and those who are following this thread. I’ll keep you posted with the outcome, but not till later in the week, when I can get back to the Blazer.
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Old 10-11-2020, 11:27 PM   #7
'68OrangeSunshine
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Re: Stock 250 CID / I6 Alternator wiring picture

Probably the Solenoid. Redundant ground straps never hurt either. Battery connections...
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Old 10-12-2020, 12:35 PM   #8
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Re: Stock 250 CID / I6 Alternator wiring picture

Really not much to wire up .
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Old 10-12-2020, 01:22 PM   #9
FLBLAZE
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Re: Stock 250 CID / I6 Alternator wiring picture

Thank you Mark. This is visual confirmation that I got it right. What threw me off was the bracket that ties-in the the bolt which appears to do nothing other than keep the wires tidy.
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Old 10-12-2020, 04:47 PM   #10
'68OrangeSunshine
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Re: Stock 250 CID / I6 Alternator wiring picture

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Thank you Mark. This is visual confirmation that I got it right. What threw me off was the bracket that ties-in the the bolt which appears to do nothing other than keep the wires tidy.
When you mount it on the Negative stud, and top it with the black ring terminal, and slip the tab into the slot, it grounds the casing to the Ground circuit.
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Old 10-12-2020, 04:52 PM   #11
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Re: Stock 250 CID / I6 Alternator wiring picture

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Youíre right RustyPile. The alternator was not technically replaced. I changed the belt and removed the alternator due to stripping the threads in the top / bracket position, only to find out from someone much smarter on this very forum, that all I had to do was replace the screw with a longer version and tighten it with a bolt. But by then I had already removed the wire connections to the alternator... �� All this to say that Iím confident itís not the alternator. Iíve got a couple of ideas to try out based on what I did. So I appreciate your help and those who are following this thread. Iíll keep you posted with the outcome, but not till later in the week, when I can get back to the Blazer.
Help me understand what you have going on....... Before you started working on the belt replacement, the truck started and ran fine?? You did all that work replacing the belt, got the alternator wires hooked correctly and now when you attempt to start the engine, the starter engages and cranks the engine over but the engine doesn't start and run???? Do I have it correct??
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Old 10-12-2020, 05:00 PM   #12
72c20customcamper
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Re: Stock 250 CID / I6 Alternator wiring picture

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Thank you Mark. This is visual confirmation that I got it right. What threw me off was the bracket that ties-in the the bolt which appears to do nothing other than keep the wires tidy.
The black wire goes under the tab to make contact with the alternator.
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1968 c20 stepside
1977 Suburban sold
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Old 10-12-2020, 05:08 PM   #13
'68OrangeSunshine
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Re: Stock 250 CID / I6 Alternator wiring picture

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The black wire goes under the tab to make contact with the alternator.
I put the tab on the bracket into the slot on the back case of the Delcotron, with the hole over the stud, then mount the Black lead ring terminal on the neg. stud over it and secure with the nut. The bracket is a combination ground connection and harness protector. Fit is better in this sequence.
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Old 10-12-2020, 05:26 PM   #14
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Re: Stock 250 CID / I6 Alternator wiring picture

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I put the tab on the bracket into the slot on the back case of the Delcotron, with the hole over the stud, then mount the Black lead ring terminal on the neg. stud over it and secure with the nut. The bracket is a combination ground connection and harness protector. Fit is better in this sequence.
If you look at mine the ground is clearly under the harness clamp . I would trust a copper connection to the alternator than a rusty zinc plated 28 gauge clamp . Just my experience and practice . But really it shouldn't matter a car will run without an alternator hooked up
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1969 AMX ,
1968 c20 stepside
1977 Suburban sold
68 anniversary.
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Old 10-12-2020, 11:06 PM   #15
'68OrangeSunshine
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Re: Stock 250 CID / I6 Alternator wiring picture

Here in AZ, I don't have the corrosion problem. I file the bracket/keeper/tab clean with a ingnition file. But on my latest alternator, these's a flanged 3/8'' bolt threaded into the case back. I have a ground strap bolted there connecting with a motor mount bolt, that also has a bigger ground strap to the frame. Can't have too many ground straps.
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