Please help this newby! My 70 F100 is pulling 2.5 amps from the battery with nothing on. I pulled all the fuses and the current still drains. I recently had a new alternator put on and suspect either the alt or voltage reg may be the culprit. Is there a way to isolate these two to determine where the short is? I don't have a wiring diagram. (Anyone know where to get one?) Any other suggestions on how to track down where the current is going?

Thanks

 

Keep in mind about any radio clock or simular that draws constantly during the test. Start by unplugging the regulator and retest. If no draw or less draw,something is wrong with the regulator. If you had less draw but still a good amount,you will want to leave the regulator unplugged and head for the alternator. Unhook the battery each time you take one wire off the alternator to prevent an arc when your wrench/hand touch anything metal. Remove one wire at a time and retest as you go until you find something different. If you end up not finding the draw problem after every wire is unhooked from the alternator and regulator is unplugged,there should be a couple wires that are fused together within the harnesses for the regulator and alternator. Cut the harness open and inspect.Keep us posted.
Phillip

 

Phillip - Thanks! I forgot to mention that I did unplug the voltage reg and the current draw stopped. However, I figured that a short "downstream" would draw current through the voltage reg so my test didn't necessarily point to the voltage reg. Was my logic flawed (again)?

 

sounds like a bad regulator to me

Trail Rider

 

Just had the same problem with My 72 f250.First take the negative battery cable off,then hook up a circuit tester inline with the negative post and the disconnected negative battery cable.If the light comes on with the key off you have a dead short in the harness on the battery side of the ignition.If the tester light comes on only with the key on ,the short is in the keyed side of the harness.You can localize the problem by removing one fuse at a time,if you pull a fuse and the light goes out then the short is in that part of the harness.Dont forget to check the headlight harness as it will not show a short until the headlights are turned on,as well as the marker lights etc.If you leave the test light hooked up while you check the harness as I did ,I saw the light flicker and knew I had found the short in my headlight wiring harness.Remember to wear eye and hand protection when working around batteries and electricity.Good Luck Wojo. also ,I once had a radio that had an internal short and drew the battery down,so if you have your radio or any other electrical component hooked up direct drive as I do, dont forget to check them one at a time also,adios amigo!

 

I to had this problem with my 79 F-350. I found that a bad voltage regultor would drain the battery in about 12 hours. To check if this is your problem un screw it from the inner fender to ungrund it. Then check if it is still drawing current.