Chevy alternator help

justjeepin86

justjeepin86

Well-Known Member
Joined
Jul 9, 2005
Location
Winston-Salem, NC
So I swapped a serpentine setup on my tbi 350. That comes with a cs series alternator. Changing over from 2 wire plug to a4 wire plug. I've done a ton of reading and think I understand what fi do. Problem is that it's still not charging. I have the exciter wire hooked up with a resistor. I never saw a definitive resistor size though. The photo is a stretch of my terminals. The resistor just goes inline in a 12v switched wire, right?
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If it is labeled plis on the connector then p is phase for a tach, not needed. L is 12v hot through a light/resistor in parallel or resistor alone, I'd use around 500 ohm, I is ignition hot, 12v keyed with no resistor. s is the sense wire. S needs to go to the junction block where the rest of the vehicle gets its power (like the battery side of a Ford starter solenoid, the battery post on a Chevy starter, an underhood fuse box on modern injection, etc). Some people will loop the s terminalto the bat post on the alternator, but that doesn't tell the regulator what the voltage is where the load is being pulled from.

I or L you can use either one or both for redundancy, and s is required too.

If your regulator has plfs all the terminals except f are the same, f is used for a signal from the ecm for ecm controlled charging. I'm not sure if these will work if you power the L terminal and leave f alone or not, I'd need to look at my manuals.
 
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^ knowledge
 
Tim C said:
If it is labeled plis on the connector then p is phase for a tach, not needed. L is 12v hot through a light/resistor in parallel or resistor alone, I'd use around 500 ohm, I is ignition hot, 12v keyed with no resistor. s is the sense wire. S needs to go to the junction block where the rest of the vehicle gets its power (like the battery side of a Ford starter solenoid, the battery post on a Chevy starter, an underhood fuse box on modern injection, etc). Some people will loop the s terminalto the bat post on the alternator, but that doesn't tell the regulator what the voltage is where the load is being pulled from.

I or L you can use either one or both for redundancy, and s is required too.

If your regulator has plfs all the terminals except f are the same, f is used for a signal from the ecm for ecm controlled charging. I'm not sure if these will work if you power the I terminal and leave f alone or not, I'd need to look at my manuals.
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Thank you sir, much appreciated. We'll see where that gets me.
 
As a follow up, If your regulator has pl F s then you leave F alone, hook a resistor or bulb/resistor inline to 12v ignition hot to the L terminal. The F terminal is an output to tell the computer how hard the alternator is charging and If you power it thinking it is an exciter wire it can possibly burn up the regulator. So if the connector on the regulator (not the harness) says PL"I"S you can use either L with a resistor or light or I straight key voltage, or both and the sense wire. If the connector says PL"F"S you need a resistor or light on the L ignition hot and the sense wire, leaving the P and F empty.

If the alternator came off the truck you got the brackets from it is most likely a PLIS, but there is no telling what a rebuilder put in the box if it has ever been replaced. If it isnt marked or like some aftermarket regulators say P L I/F S, safe bet would be to run it through the L terminal only. I'd run a 470-500 ohm 1/2 watt minimum resistor too btw.
 
a_kelley said:
Why not just use a bulb instead of a resistor? Gives you a charging failure indicator as a bonus.
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If you have a voltmeter the light isn't really necessary, and even if you use a bulb, put a resistor parallel to it. Otherwise it will not charge if the bulb blows out.

Also it needs to be an incandescent bulb. A LED won't work properly.
 
Tim C said:
If you have a voltmeter the light isn't really necessary, and even if you use a bulb, put a resistor parallel to it. Otherwise it will not charge if the bulb blows out.

Also it needs to be an incandescent bulb. A LED won't work properly.
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Duhf course incandescent always ftw!!
 
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