I have purchased a cat 247b. Previous owner warned me of a battery draw and he always just disconnected the battery cable after turning off the machine. I have been able to find a 4 amp draw with multimeter after turning off the key. I traced it to the d+ wire on the alternator. It is only there after you cycle the key switch. If I unhook battery cable for a few seconds then reinstall the draw isn't there until you cycle the key on-off again. I have pulled fuses and relays one by one but none of them killed the draw. I tested key switch and it's fine, also took alternator off and repair shop tested it as ok. Any advice on how to find what is causing the d+ wire to remain hot after key is switched off?
Some machines have a diode in the fuse panel to prevent back feeding of alternator. If you can get your hands on a schematic, you might be able to locate it.
I have the wiring diagram and only see 2 diodes. One near the hour meter and one back closer to the alternator connection. Both diodes test good.
I have had 3 alternators that a repair shop said were good, turned out were no good. Mounted in a brand new one and end of problem. I stopped doing work for customers who get alternators or starters from that place. Might not be your situation, might be. Something down stream from your alternator is sucking power. Wondering how power could get past diode unless it goes a different route. Simon C
4 amps is quite the draw, I would think disconnecting fuses or some of the main power supplies would locate it. Cycling your key, wakes up all your computer systems, and they need time to power down, sometimes as long as 10 minutes. Are you sure your reading 4 amps and not 400 milli amps. No disrespect to your abilities.
Below is the draw I am recording with the key in off position and meter hooked in series of the battery cable and battery. I ended up unhooking the battery cable on the alternator, which is the only thing I can find find that eliminates the battery draw with the key off. The excited wire (d+) reads 12 volts with key on and zero now with key off. I have ordered a new alternator as this has to be the problem, because the battery draw isn't there with the alternator disconnected. I'll report back if this doesn't solve my issue.
I’d say your on the right path.
There are diodes inside the alternator. I would suspect the alternator being bad, IF it wasn't for the "only there after I cycle the on-off switch" thing. This problem acts as if a relay is energizing itself (output looped back to the power terminals) and feeding something that is causing the excessive draw. It may be something that a previous owner did and is not on the schematic. If the new alternator doesn't fix the problem, look for errant wires coming directly off the battery B+. That circuit will power something with a moderate to high current draw, like an A/C compressor.
HeavyEquipmentForums . Here’s a previous post, a bit long, but there are relays and power points, mentioned. Check post 15 for relay and other info.
If the moment you pull the wires off the alternator, the load drops out,my guess is that you found it. Hope your problem is what I stated in post#4 above. Keep us posted. Simon C