battery draining down

[dirk]

Morning from the uk.

i have rebuilt my 1200 3cv and put a simple wiring system on it. not the first time ive done it and all was good.
from some reason i did not connect in the second thinner brown wire from the alternator.
i have now spliced this into the bigger red wire as on the wiring loom they end up on the same line anyway and soon as i do it drains the battery.
any ideas whats going on here.  cheers