Datz350 Posted July 5, 2012 Author Share Posted July 5, 2012 My fault, it is a AMP gauge. So, what would cause my AMP gauge to go down when I press on the break? Turning on the headlights does this as well. Quote Link to comment Share on other sites More sharing options...
bjhines Posted July 5, 2012 Share Posted July 5, 2012 ohh the dreaded AMP gauge. The AMP gauge is misleading as hell. It should tell you if the battery or the alternator is producing current to run things in the car. If it is way negative then the battery is doing all the work, when you start the engine the gauge should swing positive once the alternator is spinning. That all assumes you have factory circuits in full working order. If you add circuits near the battery positive then the gauge readings will become even more confusing. Quote Link to comment Share on other sites More sharing options...
Miles Posted July 5, 2012 Share Posted July 5, 2012 My fault, it is a AMP gauge. So, what would cause my AMP gauge to go down when I press on the break? Turning on the headlights does this as well. That is normal. Next time you start the car watch the amp gauge and note which way the needle moves with no loads on the electrical system. With the engine running turn on the headlights etc. and note which way the needle moves. Quote Link to comment Share on other sites More sharing options...
Datz350 Posted July 5, 2012 Author Share Posted July 5, 2012 The AMP needle is always pointing towards the negative side, a little bit though. Every time the brakes are applied or the lights turn on the needle moves towards the center. It's never on the positive side. Quote Link to comment Share on other sites More sharing options...
Scarab73 Posted July 5, 2012 Share Posted July 5, 2012 The AMP needle is always pointing towards the negative side, a little bit though. Every time the brakes are applied or the lights turn on the needle moves towards the center. It's never on the positive side. HI, You can always visit your friendly auto parts supplier (AutoZone, Advance Auto etc) and have them check the alternator ckt. for proper output and the battery for shorted cells (load test). A proper operating AMP gauge might read slightly negative when cranking during start up, then, advance into the "+" side after the engine fires and is running. As a load is applied,(headlights, heater blower etc), the needle should swing more positive, thus, indicating a higher current draw. A corresponding voltmeter placed across the "+" and "-" battery terminals should greater than 12Vs with the engine running indicating a charging situation. If you turn the headlights on during this test, the Voltmeter should be seeing 14Vs, or more. This indicates there is more going inmto the battery than is being consumed, thus the ALT is operating as it should...charging the battery. If, as you say, its going "neg" when the brakes are applied, I suspect there is a short to ground in the taillights somewhere or an, otherwise, high resistance. Hope this helps. Quote Link to comment Share on other sites More sharing options...
Datz350 Posted July 5, 2012 Author Share Posted July 5, 2012 Great info!! I'm going to do the volt meter test tomorrow. The needle on the AMP gauge doesn't move towards the negative. When I step on the brakes the needle moves towards the positive. Same thing when I turn on the brakes. I noticed that when I apply the brakes my fuel pump skips for a bit then sounds like it slows down. Once I step on the gas the fuel pump sounds like normal. What's going on here? Quote Link to comment Share on other sites More sharing options...
Miles Posted July 7, 2012 Share Posted July 7, 2012 (edited) Great info!! I'm going to do the volt meter test tomorrow. The needle on the AMP gauge doesn't move towards the negative. When I step on the brakes the needle moves towards the positive. Same thing when I turn on the brakes. I noticed that when I apply the brakes my fuel pump skips for a bit then sounds like it slows down. Once I step on the gas the fuel pump sounds like normal. What's going on here? Remember amperage is current flow. The amp gauge measures current flow. What happens to current flow when you turn on a light or fuel pump? Fuel Pump Slows: Applying the brakes switches on the brake lights causing a voltage sag which reduces available voltage to the fuel pump. So the pump slows down. The voltage goes back up when you let off of the brakes making the pump sound normal. You may benefit by visiting your local hot rod shop and picking up a book on hod rod electrical systems. Hot rod books are helpful because they focus on electrical issues car builders have to deal with getting their projects on the road. Here is a book I found at a local rod shop (American Pastimes). You could order it from: http://www.watsons-streetworks.com/wiring_accessories.html Edited July 7, 2012 by Miles Quote Link to comment Share on other sites More sharing options...
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