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SVT Shelby GT500
Multimeter Weirdness
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<blockquote data-quote="Race Red Boss" data-source="post: 16297901" data-attributes="member: 162573"><p>I just replaced the Motorcraft battery in mine. It's date code was Feb.2018, so not very old. It *appears* that its just a bad battery, BUT....I'm not totally convinced yet. I have a battery tester and the new battery is showing much better cranking amps/cold cranking amps so far....it's also maintaining a good voltage level.</p><p></p><p>According to the YouTube's I've seen on checking for parasitic draws, the car shouldn't drawn any more than 25 to 30 milli amps when turned off. Your's looks like it's within spec....</p><p></p><p>When you disconnect the battery, and then put your multimeter probes on the battery cable lead and the battery terminal (should always do negative side to be safe), it will "wake up" the ECM and you'll see a higher draw initially (make sure you have your meter measuring high enough amps....or you'll blow the fuse and/or damage it). The amperage should lower fairly quickly ...down to the 25-30 milli amp level.....not to zero (from what I've seen). There is always some draw on the battery from the car systems, i.e. security. Reading the meter I found can be confusing. You also have to be careful how long you keep the meter attached when measuring amperage....many of the cheaper meters will say no longer than 15 secs. at a time and to wait some period in between before re-measuring.</p><p></p><p>Also, rather then pulling fuses to see if your amperage reading drops (to determine which circuit is the culprit), you can use your multimeter to measure voltage drop (using milli volts setting), by putting the meter leads on the contact points on top of each fuse. If it reads voltage.....there is amperage being drawn on that fuse. Check your owners manual for what's on that circuit.</p><p></p><p>I'm considering buying an "Amp Clamp" type meter so I don't have to disconnect the battery (which is a hassle besides also resetting your radio, etc.) to see if there is a parasitic draw....or not.</p><p></p><p>How old is the battery? Also, do you have any aftermarket stuff on the car that requires wiring, i.e. stereo, security system, sequential tail lights, etc.? Improper wiring often is the source of trouble....</p></blockquote><p></p>
[QUOTE="Race Red Boss, post: 16297901, member: 162573"] I just replaced the Motorcraft battery in mine. It's date code was Feb.2018, so not very old. It *appears* that its just a bad battery, BUT....I'm not totally convinced yet. I have a battery tester and the new battery is showing much better cranking amps/cold cranking amps so far....it's also maintaining a good voltage level. According to the YouTube's I've seen on checking for parasitic draws, the car shouldn't drawn any more than 25 to 30 milli amps when turned off. Your's looks like it's within spec.... When you disconnect the battery, and then put your multimeter probes on the battery cable lead and the battery terminal (should always do negative side to be safe), it will "wake up" the ECM and you'll see a higher draw initially (make sure you have your meter measuring high enough amps....or you'll blow the fuse and/or damage it). The amperage should lower fairly quickly ...down to the 25-30 milli amp level.....not to zero (from what I've seen). There is always some draw on the battery from the car systems, i.e. security. Reading the meter I found can be confusing. You also have to be careful how long you keep the meter attached when measuring amperage....many of the cheaper meters will say no longer than 15 secs. at a time and to wait some period in between before re-measuring. Also, rather then pulling fuses to see if your amperage reading drops (to determine which circuit is the culprit), you can use your multimeter to measure voltage drop (using milli volts setting), by putting the meter leads on the contact points on top of each fuse. If it reads voltage.....there is amperage being drawn on that fuse. Check your owners manual for what's on that circuit. I'm considering buying an "Amp Clamp" type meter so I don't have to disconnect the battery (which is a hassle besides also resetting your radio, etc.) to see if there is a parasitic draw....or not. How old is the battery? Also, do you have any aftermarket stuff on the car that requires wiring, i.e. stereo, security system, sequential tail lights, etc.? Improper wiring often is the source of trouble.... [/QUOTE]
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