Topic: Very rapid battery discharge

[db22]

Yesterday I got my '75 550K project bike to turn over with the starter for the first time.  All well and good, until it became obvious that the battery was discharging so rapidly that just three or four one-second bursts of the starter used up everything the battery had. I have two relatively new conventional lead-acid batteries, topping one up on the maintainer while using the other in my rider (also a '75 550K). I should have checked the voltage loss, but did not. The wiring harness is only partially connected, since I still need to buy new turn signals.

The bike suffered an electrical "event" at some point in the past -- when I got it, the rectifier was melted and the ground wire to the frame at the coils was burned. I used a generic rectifier with a large built-in heat sink, and soldered in some wire to replace the burned ground. I still can't get the headlight or taillight to light up. The bike is the same weird mix of parts as my rider, but was quite a bit more run-down when I got it. The harness was mostly disconnected and very dirty, and I removed it when I tore the bike down for repainting. I am using my rider as a model to hook the wiring back up, but the rider is pretty jury-rigged and probably is not a good example. I have downloaded several helpful diagrams and articles from this forum, but I'm doing this for the first time, and feeling my way through the dark.

What might cause a good battery to die after just a few jolts of the starter?

[KRONUS0100]

loss that big that fast..........first guess would be the larger diameter wire...........like the batt to solenoid, or solenoid to starter wire  is shorted to ground. could also be the starter itself is shorted.  quite possibly could be a headlight bulb wire shorted to ground.   has to be something major to dump a battery that quick.  last but not least...........................................are all the cells in the battery good, it doesnt had a dead cell?
  good luck.

[db22]

If the starter itself was shorted, would it still turn over? With all those disconnected bullet connectors and dangling wires, there is always the possibility of a short somewhere. I did blow one main fuse, but that was due to an incorrect connection in the headlight bucket rat's nest. I associate short circuits with smoke and crackling noises, but I'm sure there's a lot more to it than that.

This bike originally had a headlight switch, but the entire right switch was missing and the replacement I found is from a later model wired for headlights always on. Should I try putting a jumper somewhere in the light circuit?

Thank you for your help!

[solo 2]

Put an amp meter on it and measure the electrical draw at the battery. Do not apply starter, just measure the drain. The fuses did not blow. If it's high remove circuits one at a time until you find the bad area.

+1

Here's a great video on how to do this, much simpler on a bike as there are only a couple of circuits. This will tell you at least where to start looking.

How To Perform a Parasitic Draw Test - EricTheCarGuy

Good luck.