just installed new gauges on my 71 ss from idiot lights and tach,temp,fuel all work but the ammeter is reading 0 when the car is running with the head lights on it goes to the neg 40 side of the gauge a couple of notches is this right

The ammeter should be wired in the 10ga wire between the battery and rest of the electrical system. It will show inflow or outflow for the battery. I am not fond of ammeters because they add a lot of wire into a heavily loaded circuit. Volt meters are not so intrusive.

wire should be correct new forward light harness m&h there all factory/aftermarket gauges what should it be reading?

I think around 30+ is normal with just the engine running. With the engine running and the lights on, each light draws around 5-6 Amps I think, and upwards of 20 with the brights on so you'd be closer to 0, maybe around 15. Is this with a stock configuration alternator? With added accessories and a higher amperage alternator, it could vary quite a bit.

Agreed that a voltage gauge is the way to go, you don't want all that current passing through a gauge:noway:. I don't know why the big 3 ever did this. Dodge trucks I believe are the most recent in the 80s to route it through the bulkhead connector.....not good at all. Ammeter takes full current, voltmeter just needs a constant ignition switched 12 v source and ground, no large wires required.

Ammeter also doesn't tell you if the voltage is down, which is more important for bright lights. You may have the amperage but without voltage, things go dim.

thanks do they make a volts meter that looks factory in the dash and what could be making it read 0 .alt stock and stock radio nothing extra drawing power.

An ammeter won't show much with no low load if the battery is fully charged.
Leave stuff on for a half hour and try it.

I think you are OK. It uses what is called a shunt assembly. The current doesn't all go through the meter, just a sampling that is coupled to the meter. All meters are very low current. If the lights are on and the meter goes negative, you should be able to start it up and the current from the alternator should compensate and you should go back to about zero.

Try it with the motor off and then with it on. I agree with Dean. When it's charges you should not see much movement because the alternator is carrying the load. You are NOT discharging.

Chuck

ok now my batt is dead i remember reading that sometimes the m&h harness can have the two amm wires flip flop in the forward lamp harness and would that cause a dead batt?i disconnected the #3 wire out of the circut board connector and taped it out of the way like the converting idiot lights to gauges thread explained.

So do you have a light dash harness that has been converted to a gauge harness? Is your alternator output going to the horn relay, the factory configuration, or is it wired directly to the battery? Is the new forward lamp harness a gauge harness?

If all is wired correctly and it indicated discharge with the engine running and the battery is dead, your alternator may not be working.

If the gauge is wired backwards it will indicate charge with the engine not running and headlights, heater blower etc. on.

The current doesn't all go through the meter, just a sampling that is coupled to the meter. All meters are very low current.
Chuck

Ever have a Chrysler product????
Everything went thru the meter and then branched out.
My first experience was with my first 67 300-----only thing that would work was the power seat.
No windows, headlights, accy power, ignition---nothin.

my 82 D-150 still goes thru an ammeter (fire waiting to happen)


If the engine is idling and is showing in the neg---this would be somewhat normal (with the lights on)----but should come back up to '0' or slightly charging just off idle

yes dash harness has been converted.gauge forward lamp harness everything works fine alt seemed fine before the swap. put the charger on the batt put it in this morning and sits on 0 turn lights on and it goes to 10+ radio15 with out the car running.

It's been 30 years since I worked on my amp gauge, but let me try to remember.

First, keep in mind that the factory amp gauge is actually a voltmeter. It reads the voltage drop across a piece of wire. The higher the current, the higher the voltage drop, the higher the reading. Depending on which way the current is flowing, determines polarity across the gauge, and charge or discharge as appropriate. IIRC, the voltage drop, at 40Amps, is 1.0 volt.

As far as safety, no high current flows through the gauge. If the gauge or wiring burns up, the charging system will still function normally. It is not like a Chrysler.

The wires for the amp gauge are black/wht stripe and blk/grn stripe. They break out of the lamp harness at the horn relay and the terminal block by the battery. They originally have a very small fuse link on them. The links burn out, the gauge stops working, and a repairman often hooks them back up without replacing the link. The next time there is a fault, it's usually the printed circuit on the back of the cluster that burns....

If your gauge is reading backwards, the leads are reversed. You can reverse them at the bulkhead connector, or the IP connector.

HTH,
Dave

thanks dave i have switched the two wires and it reads 0,with the lights on it goes on the positive side ,reversed it falls to the neg side with the car off and lights on should it be reading + or - with a fully charged batt with the car running it goes to the neg side. it has agood alt and batt

With the engine not running, turn on a bunch of things (highbeams, heater on high, ect...), the gauge should show on the neg side. If it goes to the positive side you have it wired wrong. With the gauge wired correctly, anytime the gauge goes to the neg side the battery is being discharged.

Below is from one of my other posts (http://www.chevelles.com/forums/showthread.php?t=125224)

I don't think you understand how the factory amp gauge is supposed to work. The amp gauge only shows the battery's charge or discharge rate. Starting with a fully charged battery......In a amp gauge car, with the car not running start by turning on items in the car, high beams, fan blower on high, brake lights ect... the more thats turned on the farther the amp gauge will show discharge. With everything possible that was original to the car turned on, the gauge may be close to max discharge. Now turn everything off and start the car, the needle will move towards charge a little (not even to the first line) and may stay there for a min or 2, than settle close to the center mark, about a needles width on the charge side. While driving the car and everything working properly this is where the gauge will normally be. Now turn the car off, turn on the high beams and leave them on for 20-30 min or so to take some of the "charge" out of the battery, then turn them off and start the car. Now that the battery's charge is lower, the amp gauge will move farther towards the charge side. As the engine RPM varies, you might see the amp gauge vary the charge rate as alternator output changes with engine RPM (at idle it may be close to the center mark, at 2500 engine RPM, it may show a medium charge rate. As the battery becomes fully charged it will slowly settle close to the center mark, about a needles width on the charge side. Anytime you see the amp gauge on the discharge side with the engine running means either the charging system is not working or the cars current demand is greater than the alternators output, and you are just running off the battery. On factory high performance cars (Chevelle LS-6's, L-78's, Camaro Z-28's) these cars came with a larger deep grove alternator pulley. alternator output was lower than the the low perf cars at any given engine RPM, battery discharge at idle was sometimes a problem, especially if other accessories was turned on. .

you the man i can understand all that.this is my first muscle car and im learning alot thanks to everyone on this site. thank you all