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Caseywheels
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Discussion Starter #1 (Edited)
1991 Tahoe Extended cab-2.8 v6 5spd.. Starts ,runs & drives fine..
But when you turn the key off it stays running.
I've been popping the clutch to kill it and unhooking the battery.
Any ideas how to fix it ?
An older buddy thinks it may be a bad diode in the alternator ? Back feeding to the coil ?
 
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Been there Done it
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Is all the wiring completely original? Or over the last 30 years have a couple aftermarket components been added? Like radio, alarm, performance ignition, etc?
Could be a bad ignition switch. Gm has had more than a few issues with them. (Over 15 million GM products were recalled for bad ignition switches between 2009 and 2014). They didn't recall any built prior to their bankruptcy.
 
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I saw that happen once when somebody installed an aftermarket radio wrong. They had the battery and the ignition power wires connected together.
 

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Caseywheels
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Discussion Starter #5 (Edited)
Wiring looks original ...except it DID have a radio.. All those wires were cut & left hanging out of the dash.. No power on any of those..
The Only other "non -original" wiring I see is where they spliced the wires to the injectors on the Holley T.b.i.
👍 Sounds like I better drop the column & check that ignition switch.. ( I had a feeling that might be it )
Thank you ...
I'll let y'all know soon. 👌
 

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Caseywheels
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Discussion Starter #6
Well... After further investigation.. Everything shuts off with the key ..Except the engine.. Even after I pulled the switch from another truck to try.. No dice.. Also unplugged the alernator..then started it... Still won't shut off... I'm stumped...
 

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Sounds like whoever installed the Holley TBI also connected the ignition to not switched power. Surprised it doesn't kill your battery.
 

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This may sound odd but bear with me. How many wires are on your starter solenoid? If the answer is 2 then this idea is gone, but if you have 3 then disconnect the yellow wire. The big red is from the battery and is the main power, the purple ( sometimes faded to brown) is for starting the truck, but the yellow is a ignition bypass which gives the coil power bypassing the resistor. It was an old trick when older batteries were unable to provide enough power to the coil while cranking to get enough power. For some reason GM kept wiring many vehicles this way well into the 90's You dont need this wire but don't let it touch things as it is hot when the ignition is on. Oh and if removing this wire stops your problem... you need a new starter.
 

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Caseywheels
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Discussion Starter #9
Nope.. Just the Red & a purple + the batterycable on this one.. Thanks for the info ...Now this is gone sound hokey..But it's "fixed" ..

I kinda gave up.. & did a "Farmer fix "...I cut the power wire to the coil and wired in a toggle switch ..
Also installing a main battery cutoff switch (like what they use on drag cars) just to be safe..

Thanks 👍
 

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Did the same on my 97 Blazer a few years ago rather than throw money at a new ignition switch for a winter beater. I didn't even bother to cut the original wire. Just added a switch.
 
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