[stan65]

i know this has appeared a million times, but i can't find a simple answer to my simple question. i have a 65 malibu that i have added ss guages to and i want to hook up the ammeter and need to know the correct location to hook the wires to not the guage end. the gm manual only shows from the guage to the bulkhead at the firewall. currently one is hooked to the horn relay and the other is at the pos junction by the battery (on radiator support) it seems to work,but i have a draw on the battery when car is off,but i changed alot of wiring and added a custom autosound hidden audio unit(memory wire?) thanks.

 

[John_Muha]

Sorry can't help, but a friend of mine owns both a 64 and 65 with gages. Tells me that the 65 is different than a 64 but never explained what was different.

 

[gregt]

i just did the same switch with my 65 elky,while putting a complete painless wiring harness,the tech suggested not to use the ammeter,he said there was a high risk for catching the wiring on fire. i installed an aftermarket voltmeter. here's the tech number for painless wiring 817-244-6898 they can give you all the information your lokking for

 

[David Bates]

There is absolutely no problem or risk using the factory ammeter in your 65. It is not an ammeter in the true sense but really a voltmeter that measures the voltage across a "shunt" resistor in the forward lamp harness so there is no risk like there is with a conventional ammeter where every bit of current drawn by the electrical system flows through the ammeter circuit in the instrument harness. What you need to make it work are two things: 1)an instrument cluster harness for an SS car and 2)a forward lamp harness for the same. Both are available from M&H Eleectrical Fabricators at - http://www.wiringharness.com/
I can personally vouch for the quality of all their 1965 harnesses. I bought an SS instrument cluster harness, a Z16 Engine Harness modified for an HEI, and a Forward Lamp Harness modified for a single wire alternator (no external regulator) moved to the right side (69-later style) and had "Plug-it-in-and-drive" results.

 

[stan65]

I appreciate all the info, but I have the harness for the ss under the dash. everything under the hood works looked the same the only difference I saw in the manual was the additional wires for the ammeter for the under hood harness I was just wanting to verify the correct placement for the underhood ammeter wires thanks again.

 

[chevy302dz]

I'm not sur if there's any difference in a factory gauge vs a aftermarket but if there's not I would hook one end to the junction and one end to the positive terminial be sure to remove the wire that already connects these 2 points. It is true that all the current will pass through this gauge so use 10 gage wire or thicker. If it is wired correctly and make sure nothing can ground out the setup is safe and much more accurate than a volt meter.

 

[David Bates]

Dave, here is a schematic, hope it helps. http://people.ne.mediaone.net/bates150/Ammeter_shunt_s.jpg
Chevy302dz, All current does not flow through this meter, please read my previous post. The ammeter wire in the SS harness is only 18 guage, hardly enough to carry even part of an alternator's current capacity. This ammeter is really voltmeter. Take a look at the schematic above and you will see what I'm talking about. The alternator output terminal is connected to the horn relay terminal and not shown in this abbreviated schematic. During a "discharge" condition such as the ignition key in the accessory position with the CD player blasting, current flows from the positive terminal of the battery through the shunt and eventually to ground. The voltage "dropped" across the shunt resistor shows up as a discharge on the instrument cluster ammeter. With the engine running and the alternator charging, current flows from the alternator (More positive) through the shunt to the positive terminal of the battery (less positive). The voltage drop across the shunt is now opposite (positive) relative to discharge and the ammeter reads charge. Shunt resistors such as the one in this example are widely used throughout industry, automotive included. Ammeters are not really a good indicator of charging system health and consequently most auto manufacturers switched to voltmeters.

[This message has been edited by David_Bates (edited 03-14-2001).]

[This message has been edited by David_Bates (edited 03-14-2001).]

 

[chevy302dz]

As I said in my post I wasn't sure if the factory installed ampmeter is a true ampmeter or not but if it was then all current should pass through it in fact it does not you won't get a accurate reading I have never dealt with a guage pak in a Chevelle and was just providing the relvent info that I had

 

[stan65]

that's great guys , but the link to the diagram p 12-54 is a nova and the chevelle p 12-45 to 12-48 doesn't show a shunt as a matter of fact if you look on 12-45 it doesn't even show any wires coming out of the firewall bulkhead plug (bottom plug left upper and lower pins?) all i want to know is where to hook up the wires to (that are missing from an idiot light harness and I have added ) I have one hooked to the horn relay and the other to the pos terminal of the battery. it seems to work great i just wondered if it is correct because of all the worries about ammeter wiring. the wiring in the manual shows 20ga, but i used 18ga with 6" of 22ga fusable link on each end. thanks

 

[David Bates]

Stan, I know the link was for a Nova, but that's the only printed reference I have. I know the Chevelle manual does not show where the wires are connected but I can assure you they go to the same place as the Nova (the positive side of the ammeter to the horn relay terminal and the negative side of the ammeter to the positive battery distribution block by the battery on the radiator support).
Chevy302dz: The meter will be accurate. The whole idea is if the charge/discharge current passes through a known resistance (ie. the shunt) you can monitor the voltage drop across the shunt and using ohm's law, calculate the current and calibrate a voltmeter scale to correspond to this which is how GM does it and it will be very accurate. I work in a Calibration Laboratory and one of the devices we do is .... current shunts which we hold to +/- .1% accuracy. The "ammeter" in early Chevelles/Chevrolets/Novas/Camaros etc. is a voltmeter calibrated to indicate current/amps in this fashion (not read amps directly).

 

[65elcamino]

David,
I agree with you on the connections being identical for the Chevelle as for the Nova. The information you have provided is correct about current shunts acting as voltmeters. Thanks for supplying the diagram of the conections.

Maybe you can help me with a different problem with this ammeter issue. I unfortunately did not realize this current shunt for what it was during my restoration and replaced it with a ballast resistor. Of course I now know this will not work to source the Millivolt signal to the gauge to operate the needle.

Can you supply me the data to select a replacement current shunt. The originals are no longer available and if by a very long shot, you can find someone with one, they want to rape you for it.

Stan65,
Do you have a current shunt wired into the circuit?

From your posts, it does not appear that you do. If this is true, I would be concerned about electrical fires due to routing all of the alternator current through the gauge. If I am wrong and you do have an original current shunt, would you please measure it and post its resistance value? Please disconnect all wires from it, so that only the current shunt resistance is being measured.

John_Muha,
Could you have your friend measure both of his current shunts? Please disconnect all wires from it, so that only the current shunt resistance is being measured.

 

[Coppertop]

Anyone in for some electronic theory?

Assuming the ammeter (actually a tiny voltmeter) needs .5 volts for a full deflection (-.5 for one way, and .5 the other way--remember there are 2 extremes--discharge and charge)

Anyway, about .5 volts for full deflection. This means at the "extreme" condition, you need .5 volts going to the ammeter.

Assuming "full-load" in your car is 60 amps, the shunt resistor needs to have .5 volts across it when 60 amps are flowing thru it to provide the meter in your dash with enough potential.

OHM's LAW E=I*R

.5 volts divided by 60 AMPS = .0083 ohms

The shunt resistor would have to be about .0083 ohms--barely any resistance.


You also have to consider the equation for power for safety on that resistor.

P= I*E 60 amps (max) X .5 volts (max) =

30 WATTS MINIMUM rating on the resistor.

So you'd need a .0083 ohm resistor rated at at least 30 watts.

On the later chevelles the ammeter connected to the battery junction and the horn relay for each wire. The wiring between them served as the "resistor" that had a voltage drop across it to feed the ammeter.

I DON'T know the specifications on you guy's cars. Those #'s are examples--I take no responsibility on the accuracy. Just to give you an idea.

 

[stan65]

well here it goes. all I did was hook up wires to the horn relay and the dist. block. as I am not an electrical genius I'll give a laymans idea. as the pos dist block and the horn relay are both pos. the entire current used by the car isn't going thru the gauge and the way I see it the gauge is only reflecting the potential difference between the two places.my car has factory power windows and air. when I have all the windows up and still push up with the a/c & headlights on it shows about 90% discharge and when released shows about 25% charge for about 30 sec then goes to almost 0 all with the car running so the shunt (or normal resistance of the harness) must be ok as I haven't had any real problems and I never even thought of an "ammeter" actually being a volt meter but it makes real since after giving thought to the wiring thanks I think I finally got it. maybe somebody can do a wiring diagram like wess did on the i think 70 chevelle.