Charging Issue (72 Blazer) - The 1947 - Present Chevrolet & GMC Truck Message Board Network

snuff · 01-29-2007, 01:17 AM

Just purchased a 72 K5 Blazer, and it turns out there is a charging issue. While the motor is running, I only read 12.5 volts on the system (freshly charged battery) opposed to a normal 14.2 volts. I have replaced the Alt, Reg, and it has a new battery. I am told that on the alt, the F term should read 12 volts when the ignition is on. Well, I'm not getting it. On the reg, I am only getting a 12 volt reading on the number 3 terminal which I understand is the cable running from the Alt to the battery. My guess is possibly the wire running from the ignition to the regulator? What are your thoughts. I appreciate any help. Thanks in advance.

krue · 01-29-2007, 01:20 AM

I'm not much good on the electrical stuff, but I would like to welcome you to the board.

**Yukon Jack** · 01-29-2007, 10:35 AM

Welcome to the board and post a pic of your K5 when you can.

For your question, post it over here and you are more likely to get more knowledgeable responses - I for one can figure out simple electrical stuff, but am pretty clueless on electrical issues.

LUV2XCLR8 · 01-29-2007, 06:04 PM

From West TN

hotrodhomi · 01-29-2007, 06:24 PM

Can you take the alt back and upgrade it to a "one wire"?

Burt4x4 · 01-30-2007, 10:31 AM

If you get a one wire alt you can bypass that external reg. Plus you can get a high amp alt if you switch to a one wire type. Use like a 8gage wire strait from the alt to your batt.

You may have a bad ground or a loose wire so I would double check all your connections and clean the plugs/connecters. Spin up the RPMs to about 1200 and check the voltage at the alt charge wire on the alt..should be up in the 14v area if it is but your batt is still at 12 then you know the regulator or the wires are bad or open...
Good luck

snuff · 02-05-2007, 12:13 AM

Thanks for the help guys. I ended up going with a one wire alt, and its working fine.

01-29-2007, 01:17 AM	#1
snuff Registered User Join Date: Jan 2007 Location: Colfax, CA Posts: 9	Charging Issue (72 Blazer) Just purchased a 72 K5 Blazer, and it turns out there is a charging issue. While the motor is running, I only read 12.5 volts on the system (freshly charged battery) opposed to a normal 14.2 volts. I have replaced the Alt, Reg, and it has a new battery. I am told that on the alt, the F term should read 12 volts when the ignition is on. Well, I'm not getting it. On the reg, I am only getting a 12 volt reading on the number 3 terminal which I understand is the cable running from the Alt to the battery. My guess is possibly the wire running from the ignition to the regulator? What are your thoughts. I appreciate any help. Thanks in advance.

01-29-2007, 01:20 AM	#2
krue Designated A-hole! Join Date: Mar 2003 Location: South Mississippi Posts: 36,448	Re: Charging Issue (72 Blazer) I'm not much good on the electrical stuff, but I would like to welcome you to the board. __________________ "If it ain't broke, fix it 'til it is!" Being stupid ain't illegal. We're Still Debt Free Except for the House!!! www.daveramsey.com 70 GMC SWB Stepside project "Green Booger" soon to be 6.0l/4l80e 93 S-10 "Poppaw's Truck"

01-29-2007, 10:35 AM	#3
Yukon Jack Post Whore Join Date: Feb 2000 Location: Rose Hill, KS, USA Posts: 12,686	Re: Charging Issue (72 Blazer) Welcome to the board and post a pic of your K5 when you can. For your question, post it over here and you are more likely to get more knowledgeable responses - I for one can figure out simple electrical stuff, but am pretty clueless on electrical issues. __________________ 1970 Blazer with a 400 sbc and 4" lift 1980 Pontiac Trans Am, 455 Oldsmobile 2012 Kawasaki Concours 14

01-29-2007, 06:04 PM	#4
LUV2XCLR8 The LuvShack Garage Join Date: Jan 2004 Location: Maple Grove, TN (West Side) Posts: 30,468	Re: Charging Issue (72 Blazer) From West TN __________________ Owner/Op: "TN Classic Transport Carriers" The Toy: "Square Vette" 72 Hybrid Blazer Toy Barn: "LuvShack" 40 x 60 x 20 Shop Tow Piggy:"Maddy" 88 Silverado 3500 Hauler: "Feathers" 14 Aluma 8218T

01-29-2007, 06:24 PM	#5
hotrodhomi Registered User Join Date: Apr 2004 Location: Sacramento Posts: 3,737	Re: Charging Issue (72 Blazer) Can you take the alt back and upgrade it to a "one wire"? __________________ '72 2wd blazer, bagged w/ watts link & EDC '72 C10 "Lowered Farm Truck" STOLEN 5-18-11 '66 impala ht

01-30-2007, 10:31 AM	#6
Burt4x4 Registered User Join Date: Feb 2000 Location: Modesto, CA Posts: 1,842	Re: Charging Issue (72 Blazer) If you get a one wire alt you can bypass that external reg. Plus you can get a high amp alt if you switch to a one wire type. Use like a 8gage wire strait from the alt to your batt. You may have a bad ground or a loose wire so I would double check all your connections and clean the plugs/connecters. Spin up the RPMs to about 1200 and check the voltage at the alt charge wire on the alt..should be up in the 14v area if it is but your batt is still at 12 then you know the regulator or the wires are bad or open... Good luck __________________ 1972 K5 MPFI454/Sm465/Np205/D60/14FFd/Re-Centerd H1s w/Swamper Iroks

02-05-2007, 12:13 AM	#7
snuff Registered User Join Date: Jan 2007 Location: Colfax, CA Posts: 9	Re: Charging Issue (72 Blazer) Thanks for the help guys. I ended up going with a one wire alt, and its working fine. Last edited by snuff; 02-05-2007 at 12:14 AM.



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