Where does the little silver box mount on a 76dt400 and has the one wire coming out of it 

Someone wil be along soon. But my undertanding is it belongs in with the yellow so saves the magneto powered bulbs & stops overcharging of the battery too. So if you have it mounted in original place on the bike [if it came with one--or this one] there should be a yellow close by. Others will know that model far better than me, even though i assembled them new & serviced them. But of course they never gave any trouble when new. Now they're coming back to bite us haha. I'm in NZ by the way & wiring differs on our in some ways but probably not in regards to the regulator. Your's might have a battery powered tail light where ours is part of the headlight circuit. Welcome if you're new!!. I'm just assuming your in the US. Cheers.

Silver box is your voltage regulator , for your headlight .
Your 75 service manual was probably of no help , as 76 was first year they were fitted as OEM .
My parts book shows it mounting to the chassis in the steering head area ,
between the High Tension coil and the Horn . I can't be more specific ,
as there are only arrows pointing to the vicinity of mounting position .
There should be mounting lugs or threaded holes there , so I'm sure you'll sort it out .
 

Yeah there's a wire there it was hooked up I can hook it back up the problem was there was no airbox I put the airbox back in and now where they had it mounted is where the airbox mounts and I can't find any place there's a two bolt mount to match it in the book it shows it's up by the coil but that doesn't make any sense there's no amount

Is it mounted under the airbox itself with an earth wire to the regulator body as has to be earthed to work.

My guess is you bought a used airbox?  I'm 99.9% sure it was mounted on airbox like RT325 said. 

1975 airbox would be the same except for the regulator bracket.  1976 had the bracket. 

Update:  Just found a pic of a 76 airbox on ebay and bracket is there so RT325 is correct. 

 



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MarkT wrote: " Update:  Just found a pic of a 76 airbox on ebay and bracket is there so RT325 is correct. "

Thanks.  Now I know where mine goes when I get around to assembling my avatar!

Don't forget the earth wire if the filter box is plastic--well even if its not plastic considering possibilites for a bad earth mounted there.

I just replaced the 6v system on  my 400 with a 12 volt one - everyone is right about the position of the regulator being on that bracket on the air box.

One helpful tip, although there is an earth lead going to the unit, I recommend running another one from the engine - I used the decompressor bracket bolt to contact the engine to that earth point and then another to the ign coil.

Aparrently not having a earth lead to the engine causes a lot of electrical problems.

After I converted to 12 volts, the battery was being overcharged, fitting the engine earth lead as described fixed that - so guess if it affects the 12 volt conversion, it is worthwhile doing if you are still running 6 volts.

Just thought I would mention it.