Amp guage pegs - The 1947 - Present Chevrolet & GMC Truck Message Board Network

tom hand · 12-12-2003, 01:40 PM

My amp guage has never worked....I have read on this board several times that there are two little fuses that are usally the culprit. Changed them last weekend and low and behold the gauge works. I have changed over to a bigger one wire internaly regulated alternator. At idle it reads just a hair to the right of center, right where I would expect, but as soon as the rpm's come up a little it pegs out. Anyone else have this problem?

Perchjerker · 12-12-2003, 03:53 PM

Sounds like your alternator is overcharging your system. Does you battery smeel bad after driving it for a while. Be careful, an overcharged battery will EXPLODE--ask my grandma!

Mike C · 12-12-2003, 04:29 PM

Does it return to center after driving a short while? May be the the alternator is ouputting more than the gauges range. But as the battery voltage returns to near normal after cranking, the needle should return to center unless you have some extremely large power drain somewhere.

Or something in the wiring causes the gauge to no longer read correctly. I had posted several years ago about the amp gauge and whether it still functioned after bypassing the external regulator or if further changes had to be made. Don't remember ever getting an unequivocal answer to this.

fast14 · 12-12-2003, 05:51 PM

Where are the fuses for the amp gauge again??

**john** · 12-12-2003, 06:11 PM

Heres a diagram. One is located close to voltage reg on rad. support and the other by batt on pass side .
MIKE C My ammeter works with internal reg alt with no probs John

Mike C · 12-12-2003, 11:50 PM

How did you do your int reg John? Did you jumper the external regulator plug? Or just bypass it completely?

BobbyK · 12-13-2003, 03:17 AM

Factory amp gauge will NOT work with a one wire alt.It will hover just past midline but it is not working.

I had a one wire and thought my amp gauge was working untill I went back to the 3 wire factory alt.

Now my amp gauge give me accurate readings.

It has to do with the 2 black wire(the one's with the 4amp fuses).One wire take a reading from the alt and one from the battery.The differance in those two readings will give you either a charge or discharge reading ot the amp gauge.

With a one wire alt the only reading your getting is the one at the battery.

Mike C · 12-13-2003, 12:05 PM

Alright Bobby, how did you wire it up? I'll do a one wire in the Jimmy because the ammeter is gone and I have an autometer volt meter, but in my truck I want to have the OEM ammeter working.

BobbyK · 12-13-2003, 12:26 PM

Mike,just wire it up like the schematic above.

If you have the factory wiring just make sure the two 4 amp fuses are good and things should work.

If the fuses are good but it doesn't work check the connections at the back of the gauge.

Also check the back of the inst. cluster.Sometimes the plastic circuit board on the back can get fried(if a short takes place) and will knock out the amp gauge circuit.

If you don't have the factory wireing and REALLY want that amp gauage working run a fused 18g wire from the battery to one side of the amp gauge then another fused 18g wire to other side of the amp gauge coming from a chargeing source.

The factory makes that connection in the wire harness.This connection actually connects the battery charge wire,the out from the alt.,the "voltage sense" wire and one side of the amp gauge.All crimped and soldered in the wire harness.Find that spot in the harness and attach that wire there.

12-12-2003, 01:40 PM	#1
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	Amp guage pegs My amp guage has never worked....I have read on this board several times that there are two little fuses that are usally the culprit. Changed them last weekend and low and behold the gauge works. I have changed over to a bigger one wire internaly regulated alternator. At idle it reads just a hair to the right of center, right where I would expect, but as soon as the rpm's come up a little it pegs out. Anyone else have this problem? __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

12-12-2003, 03:53 PM	#2
Perchjerker Beer Power!!!!!!!!!! Join Date: Nov 2003 Location: Nacogdoches, TX Posts: 280	Sounds like your alternator is overcharging your system. Does you battery smeel bad after driving it for a while. Be careful, an overcharged battery will EXPLODE--ask my grandma! __________________ Rather be fishin'

12-12-2003, 04:29 PM	#3
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,727	Does it return to center after driving a short while? May be the the alternator is ouputting more than the gauges range. But as the battery voltage returns to near normal after cranking, the needle should return to center unless you have some extremely large power drain somewhere. Or something in the wiring causes the gauge to no longer read correctly. I had posted several years ago about the amp gauge and whether it still functioned after bypassing the external regulator or if further changes had to be made. Don't remember ever getting an unequivocal answer to this. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax Last edited by Mike C; 12-12-2003 at 04:32 PM.

12-12-2003, 05:51 PM	#4
fast14 Registered User Join Date: Nov 2003 Posts: 117	Where are the fuses for the amp gauge again?? __________________ Just a little crazy 1970 chevy full size half ton, soon to be one ton running gear, 350 turbo, 205 case, 355c.i.

12-12-2003, 06:11 PM	#5
john member #16 Join Date: Dec 1999 Location: Yuba City Ca. Posts: 3,618	Heres a diagram. One is located close to voltage reg on rad. support and the other by batt on pass side . MIKE C My ammeter works with internal reg alt with no probs John Attached Images __________________ john http://67-72chevytrucks.com/vboard/showgroups.php board vendors http://www.flickr.com/photos/1745471...7602865984234/ Last edited by john; 12-12-2003 at 06:14 PM.

12-12-2003, 11:50 PM	#6
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,727	How did you do your int reg John? Did you jumper the external regulator plug? Or just bypass it completely? __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

12-13-2003, 03:17 AM	#7
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,772	Factory amp gauge will NOT work with a one wire alt.It will hover just past midline but it is not working. I had a one wire and thought my amp gauge was working untill I went back to the 3 wire factory alt. Now my amp gauge give me accurate readings. It has to do with the 2 black wire(the one's with the 4amp fuses).One wire take a reading from the alt and one from the battery.The differance in those two readings will give you either a charge or discharge reading ot the amp gauge. With a one wire alt the only reading your getting is the one at the battery. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE

12-13-2003, 12:05 PM	#8
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,727	Alright Bobby, how did you wire it up? I'll do a one wire in the Jimmy because the ammeter is gone and I have an autometer volt meter, but in my truck I want to have the OEM ammeter working. __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

12-13-2003, 12:26 PM	#9
BobbyK Registered User Join Date: May 2000 Location: Petrolia,Ontario,Canada but working in Port Huron,Mi. Posts: 1,772	Mike,just wire it up like the schematic above. If you have the factory wiring just make sure the two 4 amp fuses are good and things should work. If the fuses are good but it doesn't work check the connections at the back of the gauge. Also check the back of the inst. cluster.Sometimes the plastic circuit board on the back can get fried(if a short takes place) and will knock out the amp gauge circuit. If you don't have the factory wireing and REALLY want that amp gauage working run a fused 18g wire from the battery to one side of the amp gauge then another fused 18g wire to other side of the amp gauge coming from a chargeing source. The factory makes that connection in the wire harness.This connection actually connects the battery charge wire,the out from the alt.,the "voltage sense" wire and one side of the amp gauge.All crimped and soldered in the wire harness.Find that spot in the harness and attach that wire there. __________________ 71 blazer,350SBC,approx.375HP,700R4,factory GM TPI.Dual electric fans,33x12.5x15 ATR on stock suspension. Petrolia,Ontario,Canada but working in Port Huron,MI. See ALL my Blazer pic's HERE

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