Battery Cable Help

[Goose]

I've been having trouble keeping my battery charged in my '72 GMC. So, I read the threads on the electrical forum and did the recommended troubleshooting, so far with little success. With the ground battery cable disconnected I was getting a reading of nearly the full voltage of the charged battery. So I think I have found the no Duh! I've been living with, but would like your confirmation. My ground wire from the battery is grounded to the block as required, but there is also a pigtail coming from that cable, much like the positive cable pigtail that goes to the junction box, and it is grounded to the fender. The confirmation I need is there should be no pigtail from the ground cable or at least it shouldn't be attached to anything. Anyway, that is the way I'm reading the wiring schematics. What say you? Thanks.

[72supr]

There is a pigtail on the ground wire that grounds to the fender.

[franken]

Voltage is measured across something, and current is measures by placing an ammeter in series with the load.

[teamadams]

Testing for Parasitic Load

Testing a system for current drain

To check if something is draining your battery while your ign is turned off you need to test for current, not volts. To do so, do the following:

Digital Volt Meter # YDMM05Switch your Digial Multimeter to DC AMPs. Amps is usually indicated by an "A" on the Multimeter Switch. AC is usually shown as a "~" symbol and DC shown as a "-" symbol. You usually have to move the Multimeter positive lead to a separate socket on the Multimeter. Sometimes there are 2 sockets, a high range and a low range. Always test on the highest setting first. For example: high setting on your multimeter may be 10 Amp. Test on the 10 Amp setting first, then if the current drawn is less than your Multimeter Low setting, move to that setting and keep testing. In my example my Multimeter low setting is 0.3 Amps. Also indicated as 300mA (mA x 1000 = A).

WARNING! Once the multimeter is on Amps do not connect it directly across the battery and do not hit the starter button while testing for current Amps. This will cause the internal fuse in the multimeter to blow! A multimeter set on current is a very low resistance, almost a short circuit and will draw as much current as your battery will supply till something melts. Always plug the Multimeter leads back to volts when you have finished testing to avoid blowing the fuse next time you use your multimeter.

amperage ReadingTo test for battery drain: Switch everything off on the truck. Disconnect just one battery lead. For example disconnect the Positive Battery Lead. Set your Multimeter to Amps as described above. Connect the Positive Multimeter Lead to the Battery Positive terminal. Make sure the Positive Lead you removed from the battery does not touch anything grounded, like the truck frame etc…. Connect the Negative Lead from the Multimeter to the Positive Lead you removed from the Battery. You should now see current drain measured in Amps. Move to the lower Amp setting on your multimeter if the current is lower than the setting on the Multimeter Low setting. Start to unplug the wires from radio or oyher aftermarket accessorys & fuses around your truck and see if the current reading goes to zero. This will point you in the direction of the current thief.you should have around 5 milliamps draw there is a formula based on battery amp hour rating
and the pigtail from neg batt to fender is a body ground and should be there.









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[Goose]

Yikes! Good catch. I've been measuring volts not amps. Well I've got everything disconnected now so I can reconnect one by one to find the culprit using the proper parameter. Tough gettin' old. Thanks.

[franken]

Typically, meters have 2 current sockets, one for ~100mA and one for 10A. The 10A is unfused and more than 10A will cook things.
You can take a 12V light bulb and a few wires to make a test light to be put in series w/ the load.
Might also measure battery voltage before starting after its sat, and then again w/ the engine running--may want to rev it up a bit while measuring. A charged battery is 12.6V and charging is ~13.5V.

[Goose]

Thanks, all good information. I will hopefully find my problem. I appreciate the help.

[Goose]

I have partially run the tests for current flow, but before I go further thought I would ask a question. My initially reading with everything off is 0.069 amps. There was no change when I removed the alternator wires or the voltage regulator connector. The current flow increased to 0.920 amps when I disconnected the horn relay. I don't understand that result. If the relay was bad in someway shouldn't the amperage draw be reduced when it is disconnected? Thanks for any insight.