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#1 |
Registered User
Join Date: Jan 2013
Location: Tucson, AZ
Posts: 60
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Ammeter - Shunt question
If I wanted to wire my factory 1972 ammeter, directly to my late model alternator (70 amp), bypassing the factory wiring, what size shunt would I need?
Also, if this is REALLY bad idea, please advise. Thanks. |
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#2 |
Senior Member
![]() Join Date: Feb 2001
Location: New Madison, Ohio
Posts: 21,365
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Re: Ammeter - Shunt question
I would get a shunt that would with stand 70 amps. I could be off base with this... other opinions?
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A husband can be right...or...A husband can be happy. ![]() 67-72 Chevy and GMC Trucks...The Classic Truck for the Classic Folk. ![]() 1970 CST Two tone green, 402BB, 400 Automatic, Tach, Buckets, AC, AM-FM, Tilt, GM CB, GM 8 Tract, LWB, etc ![]() ![]() JOHN 17:3...The better side of "LIFE" Remember: Everyday is a good day...Some are just gooder! |
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#3 |
Senior Member
![]() Join Date: Apr 2013
Location: Podunk, Texas
Posts: 748
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Re: Ammeter - Shunt question
I assume you talking about the fused 16-18 gauge wire that comes out of the firewall connector, and instead of unwrapping the harness near the voltage regulator to connect the wire to the 12 gauge red wire three-way or whatever connector there, you want to connect it to the 12 gauge red wire (that runs from that same three way connector) at the alternator?
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#4 |
Registered User
Join Date: Jan 2013
Location: Tucson, AZ
Posts: 60
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Re: Ammeter - Shunt question
I agree on the 70 amp capacity of the shunt, but I believe the other factor is the milli-volt capacity of the ammeter. Does anyone know this number for a factory 1972 ammeter?
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#5 |
Senior Member
Join Date: Jul 2001
Location: Muskegon,MI,USA
Posts: 6,026
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Re: Ammeter - Shunt question
I don't know the number but the factory ammeter is protected by two 4 amp fuses. It reads the amps by reading the resistance between the two connections, (approximately 3' of #10 wire).
Jim
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1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC |
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#6 |
Registered User
Join Date: Jan 2013
Location: Tucson, AZ
Posts: 60
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Re: Ammeter - Shunt question
Hmmm...build a shunt with 3' of 10 awg wire and a couple of fuses...wonder if it would work...
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#7 |
Registered User
![]() Join Date: Dec 2012
Location: Chandler AZ
Posts: 1,149
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Re: Ammeter - Shunt question
There is no way the shunt they have with 4 amp fuses in it carries full system current. Could it be a shunt of a shunt? Could it carry just 1/25 of the current and be part of a 100 amp shunt? I don't have a wiring diagram to look at that includes the shunt circuit.
When a fuse blows, the gauge quits but you don't quit charging. Just pushing this to the top so smarter than I will chime in.
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1970 Longhorn, Front Disc, 350/4 bolt, 882 heads, HEI, Edelbrock, 700R4, HO-52/4.11. 1996 Corvette, Collector Roadster, LT4, 396, 450RWHP, 6sp, 4.11/Dana44/posi 5 point roll bar And let us not grow weary of doing good, for in due season we will reap, if we do not give up. Gal 6:9 |
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#8 |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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I have to ask why?
Why do U want to run it straight to the alternator. I also would suggesting put a volt-meter gauge in the truck. ![]() ![]()
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 ![]() Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
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#9 |
Registered User
Join Date: Jan 2013
Location: Tucson, AZ
Posts: 60
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Re: Ammeter - Shunt question
I appreciate all the good information.
Shunts can be purchased from an electronics store. Question is: how many millivolts is the factory ammeter rated at? If anyone has this piece of info, it would be greatly appreciated. The reason for wiring up my own is that the PO swapped in a GM crate motor and the factory wiring is trashed. I'm just trying to get all the gauges working. |
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#10 | |
Old member
Join Date: Jan 2002
Location: Liberty, & Garden City S.C. , U.S.
Posts: 19,936
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![]() Quote:
I would still install a volt reading gauge. ![]() ![]()
__________________
1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 ![]() Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs. |
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#11 | |
Msgt USAF Ret
![]() ![]() Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,714
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Re: Ammeter - Shunt question
Quote:
I have covered this subject so many times I know it by heart. If you check the electrical section you can find all the info you need. Most of the threads on dash light to gauge conversions will cover it. Here's one of the threads......http://67-72chevytrucks.com/vboard/s...d.php?t=581719 Here's a picture showing the fusible link and the shunt with the ammeter wires and fuses. The ammeter wires go through the firewall block to the dash cluster plug on terminals 1 and 12 and then to the ammeter via the copper strips. Here is the dash cluster diagram. Note terminals 1 and 12. Here's one with the internally regulated alternator conversion with the ammeter wires.
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VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
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#12 |
Registered User
Join Date: Jan 2013
Location: Tucson, AZ
Posts: 60
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Re: Ammeter - Shunt question
VetteVet, I appreciate your vast knowledge, and especially that you are willing to share it. I am sure that you have forgetten more than I will ever know.
It matters because I think it may be better to simply wire-in a self contained shunt (if possible), rather then tap into a suspect wiring harness. By the way, is that 1.5 volts or 1.5 millivolts? Thank you again for all the info. |
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#13 | |
Msgt USAF Ret
![]() ![]() Join Date: Jan 2005
Location: Kalamazoo, Michigan
Posts: 8,714
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Re: Ammeter - Shunt question
Quote:
.........http://www.bracketracer.com/nova/shunt/shunt.htm
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VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative. |
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#14 | |
Registered User
Join Date: Nov 2009
Location: Sherman, ME
Posts: 2,359
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Re: Ammeter - Shunt question
Quote:
It's 1.5 Volts. I just tested a few spare factory ammeters I had laying around to be sure. They varied a little bit but 1.5V gave pretty close to a full scale reading on them. Like JimKshortstep4x4 said earlier, the factory ammeters are protected by 4 Amp fuses. Out of curiosity, I used my multimeter to measure the current flowing through the meters I was testing. They all had close to 2 Amps going through them at full scale deflection. That's the current that's flowing through the factory ammeter itself ... not the shunt. |
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