Power wire from battery to junction block/voltage regulator size - The 1947 - Present Chevrolet & GMC Truck Message Board Network

demian5 · 06-18-2019, 11:05 AM

I have a wire I need to replace that runs from the battery + over to my junction block (converted the harness to alternator style) on the driver side of the core support.

What size is the wire? 8ga? 10ga?

rpmerf · 06-18-2019, 12:36 PM

This is a 12 ga wire on the 67-72 trucks. 10 ga or 8 ga would be better though.

**Steeveedee** · 06-19-2019, 04:45 PM

I was looking at my truck which came equipped with a 37 Amp(?) alternator (no upgrade on the SPID). Or was there something like UY1 Camper Wiring that dictated the higher amperage alternator without it showing up on the SPID? There is a 63 Amp alternator on it now, and that is what I took off when I replaced it. I guess a 12 Ga wire is OK to carry 63A, though in house wiring that would be a bit on the small side, for my money. I don't see where anything has gotten too hot.

rpmerf · 06-20-2019, 07:04 AM

The wire that goes between the driver's and passenger's junction blocks does not carry much amperage. When the engine is off, it supplies power to the accessories - lights, HVAC, radio. When the engine is on, most of the power is coming from the generator / alternator. There is only a bit going to the battery to keep it charged.

I have had a 30 amp fuse between the battery and passenger's junction block for years. The only time it blew is when my voltage regulator died and the generator tried to overcharge the system. It melted the 30 amp fuse to it's holder.

Looking at different amp / gauge charts, I think 12ga is a little undersized. 10 gauge seems more appropriate. I am using 8 gauge.

**Steeveedee** · 06-20-2019, 10:16 PM

Yeah, I'd like up-sized wiring myself. The hot wire to the ignition has to carry 70 Amps for the starter solenoid (since that is the max current to the starter solenoid), though, according to the manual. Of course, that's with all new wiring.

AcampoDave · 06-20-2019, 10:30 PM

I can tell you from experience that oversizing that wire will cause your stock ammeter to give an exceptionally high reading. From what I have read, the ammeter is routed on what is called a "shunt" from that circuit. Changing the wire guage changes the current flow thru the guage.

demian5 · 06-21-2019, 12:19 PM

I went with 8GA. Worked fine and no longer chaffed...

Angrywood · 08-29-2023, 01:35 PM

what would be the wire sze from the junction blk to the alternator batt term? ?Im assuming 8 gage as well?

06-18-2019, 11:05 AM	#1
demian5 Registered User Join Date: Aug 2016 Location: Lake Forest, CA Posts: 2,177	Power wire from battery to junction block/voltage regulator size I have a wire I need to replace that runs from the battery + over to my junction block (converted the harness to alternator style) on the driver side of the core support. What size is the wire? 8ga? 10ga? __________________ "Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC

06-18-2019, 12:36 PM	#2
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	Re: Power wire from battery to junction block/voltage regulator size This is a 12 ga wire on the 67-72 trucks. 10 ga or 8 ga would be better though. __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z

06-19-2019, 04:45 PM	#3
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,673	Re: Power wire from battery to junction block/voltage regulator size I was looking at my truck which came equipped with a 37 Amp(?) alternator (no upgrade on the SPID). Or was there something like UY1 Camper Wiring that dictated the higher amperage alternator without it showing up on the SPID? There is a 63 Amp alternator on it now, and that is what I took off when I replaced it. I guess a 12 Ga wire is OK to carry 63A, though in house wiring that would be a bit on the small side, for my money. I don't see where anything has gotten too hot. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

06-20-2019, 07:04 AM	#4
rpmerf Registered User Join Date: Feb 2011 Location: Parkville, MD Posts: 1,024	Re: Power wire from battery to junction block/voltage regulator size The wire that goes between the driver's and passenger's junction blocks does not carry much amperage. When the engine is off, it supplies power to the accessories - lights, HVAC, radio. When the engine is on, most of the power is coming from the generator / alternator. There is only a bit going to the battery to keep it charged. I have had a 30 amp fuse between the battery and passenger's junction block for years. The only time it blew is when my voltage regulator died and the generator tried to overcharge the system. It melted the 30 amp fuse to it's holder. Looking at different amp / gauge charts, I think 12ga is a little undersized. 10 gauge seems more appropriate. I am using 8 gauge. __________________ 1970 C20 Custom Camper - 350, TH350 1997 GMC Suburban 1994 Acura Integra GSR 1987 Dodge Daytona Shelby Z

06-20-2019, 10:16 PM	#5
Steeveedee Who Changed This? Join Date: Jan 2013 Location: Simi Valley, CA Posts: 10,673	Re: Power wire from battery to junction block/voltage regulator size Yeah, I'd like up-sized wiring myself. The hot wire to the ignition has to carry 70 Amps for the starter solenoid (since that is the max current to the starter solenoid), though, according to the manual. Of course, that's with all new wiring. __________________ ~Steven '70 Chevy 3/4T Longhorn CST 402/400/3.56 Custom Camper Simi Valley, CA

06-20-2019, 10:30 PM	#6
AcampoDave Registered User Join Date: Feb 2013 Location: central California Posts: 2,774	Re: Power wire from battery to junction block/voltage regulator size I can tell you from experience that oversizing that wire will cause your stock ammeter to give an exceptionally high reading. From what I have read, the ammeter is routed on what is called a "shunt" from that circuit. Changing the wire guage changes the current flow thru the guage.

06-21-2019, 12:19 PM	#7
demian5 Registered User Join Date: Aug 2016 Location: Lake Forest, CA Posts: 2,177	Re: Power wire from battery to junction block/voltage regulator size I went with 8GA. Worked fine and no longer chaffed... __________________ "Work hard, use your vacation days." 1970 C15 GMC Long Bed 1986 C20 Scottsdale 1983 K2500 Sierra Classic Suburban 6.2 Instagram: C10sofOC

08-29-2023, 01:35 PM	#8
Angrywood Registered User Join Date: Mar 2019 Location: Orange County ca Posts: 162	Re: Power wire from battery to junction block/voltage regulator size what would be the wire sze from the junction blk to the alternator batt term? ?Im assuming 8 gage as well?



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