Hi guys I'm new here. Thanks for having me. I have a 1974 dt250. My issue is my battery is receiving ac voltage, I have changed the regulator rectifier and have the same result. Is there any other reason why my battery would be receiving ac voltage from the charging system if the regulator/rectifier is good?

That model came with a rectifier which is just a diode.  No regulator. 

How did you test the rectifier to make sure it's good and how did you determine battery is actually getting AC voltage? 

Greetings from Tennessee 

So I just changed the rectifier assuming it was bad because when disconnect my battery and test the leads going to the battery I am getting ac voltage... There is another red wire that is disconnected and if I go ground to that wire I am getting 18 volts but the voltage is DC.. so somebody must have been messing with stuff before me.. what would cause the voltage to be so high on the dc side?

It's a fixed output permanent magnet alternator.  Voltage is kept under control by balancing the output against the load on the AC headlight circuit...  The DC battery circuit uses the battery as a crude "regulator".

Without a good battery or suitable load connected DC volts can jump pretty high.  . 

Thank you. I'm trying to sort one thing at a time. I had the bike running and the tail lights were working both running and stop light. For no reason all of a sudden the tail light stopped working. When I test the voltage I'm getting nothing at the taillight.. also getting no voltage to the wires that should be connected to the turn signals.. basically no power to any DC powered lighting.. battery has juice. My instinct says something with the key switch but I'm kinda stumped as to why the dc circuit basically stoped working

 from near Salisbury, UK.

You shouldn't have any spare red wires. Attached is an image of under the seat on my own bike, where the fuse sits. Have you blown the fuse, blown the bulb(s)?

Do you have a meter that tests resistance? If you have then, on the X1 setting, resistance with your + wire to the + terminal on the rectifier, and therefore - to -, should be in the region of 5 to 9 ohms. With the wires reversed, there shouldn't be any reading.

DC you say is 1/4 bridge AC rectified.

Meter is seeing zero to +4-12 volts every other time.
It will read that as AC voltage ON AC MODE but reality is it's a pulsed DC waveform.
Battery will soften the pulses and bias to battery voltage.


cliff

Cliff - I'm not sure a meter will recognize the rectified "pulsing DC" incorrectly as AC voltage.  That's why I asked how it was being determined that the power was AC to the battery? 

(As often happens, my questions didn't get answered so who knows what the heck is going on. lol)

Since another red is now identified as 18v DC (assuming with engine running), my wild guess is maybe someone wired the battery to the AC headlight circuit because the red from rectifier is disconnected?  I'm also guessing the fuse holder is missing and that's what provided the "opportunity" for someone to re-wire the battery to AC.  Or the initial information given was just a complete mistake. 
If the battery is not connected to the correct "red", it can't power the DC circuits... 
And if some well-meaning person connected the battery to the AC circuit without a rectifier diode, the battery will drain itself through the mag coils...  hopefully not burning up the mag coil in the process....  so possible battery lights quit because battery is now dead? 

Way more questions and without pics and/or more information and answers, hard to say what's really going on. 

Recently been tracing problems on my ls3 100 & on opening the loom I can see much joining of wires where they flex at the steering head. Is a bike I got from an old workmates & we were often fixing that exact issue at work in the yamaha shop on customers bikes. Not so much on bigger trail bikes though. Just food for thought. I was referring to post #6 tail light stopped working.