I prefer the positive side myself

 

You get the same results either way, but by using the Negative, you reduce the risk of touching the leads or the clips and grounding them out, with the associated sparks and instant welding. I learned this from this excellent YouTube video.

 

pos side gave me more accurate readings

 

How accurate do you want it to be? With the key off and all fuses in, it showed 0.00 Amps this morning. Sure you can get away with using the Positive in the Corvette battery box, because there's nothing metal there, but any other car, it would be an issue. So you can use the Positive without risk, but only on these cars and nowhere else., because there's plenty of metal in the engine compartment, where most batteries are mounted.

Finally, as a note to Mr. Dawson. If you're still getting a parasitic draw on the battery. then I'd recommend that with the key off, pull the fuses one by one and measure the amperage across each set of fuse terminals. That will show you the current going across that particular absent fuse and you can then narrow it down further.

 

I like the positive side simply because the negative side is usually a pain to locate, especially on the corvette, when Im getting down to locating the specific issue whether its a parasitic draw or any other type of electrical issue. If the ground is bad and it pulling though another system sometimes you can spot it

 

It doesnt matter positive or negitive for the reading. There is no intake exhaust relationship regards to this test. Current measurement is the same from the negative use or the positive. With electronic cars the old wives tale about causing airbag failures by using the positive cable first off last on holds no water either. The reason is saftey. I get it the C3 is a pain to hook up to but most every other car on the planet isn't. Forming bad habits may one day hurt you. I've seen wedding rings and wrenches cause some serious burns by going for the positive lead fist.

 

Everyone has their own methods of seeking things out. I'm only pointing out, that the Negative cable on the battery is right there and easy to use as a starting point. As far as bad grounds anywhere else on the car, that's why I have a Power Probe 3 to identify them, quickly and easily. For checking the current across the fuse box, no need to have the other lead hooked up the positive battery cable (and in fact, would be bad mojo). With each individual fuse removed, you simply put the leads across the fuse terminals to see if any current is flowing between the two fuse clips at all. That is how IMHO, you check for parasitic draw to the individual circuit. I just did this now with the Aux Fuse Panel that runs the various aftermarket options I've added. I used the A/F ratio gauge as I guessed it to be a low current draw. Just trying to help here. Former Electronics Technician and I do auto electrical on the side.

AEM A/F Ratio Gauge with fuse pulled and Ignition OFF. Multimeter set to 10 Amps. 0.00 Amps shown:




AEM A/F Ratio Gauge with fuse pulled and Ignition ON. Multimeter set to 10 Amps. 0.13 Amps shown:

 

I was taught to use the Negative leads for doing current measurements. I have two Fluke multi-meters and they are very accurate (and $$) one of them I get re-calibrated every three years. A current Shunt is my favorite way of measuring current accurately. The shunt is a calibrated piece of materiel between two posts. I use them with either digital or analog meters and they are very, very accurate. I was in the Photovoltaic Solar Business where we were dealing with lots of low current applications.

Remove the battery from the car and watch it for a week or two (don't expect many people driving their Corvettes this week) and measure the voltage every few days. A new AGM battery should have a very low self discharge. If the battery has an internal short or defect watching it on a bench would be the best way of catching it.

If you are going to measure each circuit then I would get the Harbor Freight Fuse device that shows the current being drawn through the circuit. They plug in to the fuse socket and have a small display that shows the current flowing through the circuit. They make them for 12 volt, 20 or 30 amp circuits and are not expensive.

 

You can use the mV selection on your meter and read across the fuses looking for a voltage drop which will point you in the right direction for the drain also. Test driving getting the car hot and leaving your meter hooked upped over night in the "Min-Avg-Max" setting will also save you a lot of time as well. Performing a thorough charging, drain and battery test should take about 15-30 minutes

 

Properly using your tools is not a bad habit. If you are working the battery you should have your ring off in the first place. Yes in 1985 there was a NAvy safety alert with a picture of a guy that welded his wedding ring to a open lug and lost the finger at the ring....You arent going to do that testing your radio. YOu will at the battery so you always remove the ground firs....that doesnt tell you to test the component from the ground side. So instead of being preachy, use the tool correctly with the proper shields on the probes and you wont get a booboo.

 

As was pointed out, the current doesn't care, as long as the circuit is complete. And in a C3, even though the battery location makes a positive-side reading safer than in almost any other cat, that still isn't best practice. And for those of us with a quick-release screw on the negative terminal, why complicate things, or develop testing habits that would be less safe in any other situation?

One additional tip, if you unbolt the driver-side seat, and lay with your back on the floor, and your feet under the back window, it may be a bit easier to test all of the fuse leads. While looking for a better way to do this in my car, I discovered this tool that works with modern fuses. Perfect for a 79+. Perhaps there's an equivalent for glass fuses, or you could make an adapter. Inside the part that plugs into the fuse panel must be a calibrated shunt, so only voltages are sent to the remote read head. Simple and safe!

 

If you are going to be doing anything with your hands, either don't wear a ring at all, or wear a silicone ring. One of my cars requires you to slam the frunk, so no scratches doing that, either.

 

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