Look carefully at your bridge rectifier - the AC input & DC outputs are
almost always clearly marked.
The DC polarity will be marked, but if you can't be sure the longest output
pin is by comvention DC +
Remember AC is sometimes labelled by a "wiggly line".

The transformer is best examined IMHO using a "multmeter" (test meter) set
to AC in the voltage range 0-20 or whatever is most suitable to measure
around 12 VAC on your meter.
I would expect you can confirm the two terminals most distant apart (IE
excluding the centre tap terminal) will show you the higher voltage you
seek.
I can't quite recall if the AC RMS voltage will read 12 or about 14.5 but
after rectification & some smoothing you should see 12VDC.
Pete


Check the output terminals first
"dwbauer" wrote in message
. ..
I am attempting to replace a bad transformer in a 12v battery charger. I
went to Radioshack and purchased a 12v transformer and a 4 amp full wave
bridge, but I don't know how to connect it. The transformer is center
tapped
Primary is 120v Secondary is - 6.3 - 0 - 6.3, 3a the bridge is marked +
AC - with four leads (|=leads)
e.g. | + | | AC | - |
I have three leads from the transformer, two yellow and a black center.
What do I do with the transformer three and four on the bridge?
Thanks for any help to a dummy; Don