I been restoring my 75 DT250 for 2.5 years now and im having some issues with the electrical. I have a new rectifier, new voltage regulator installed as stated in the tech library, new flasher relay 3 prongs, new battery fully charged. I currently have everything working except my flashers are flashing too quickly and the taillight is flashing as well. I have been reading up on these issues but i just cant seem to figure it out. The taillight flasing doesnt turn on and off. With the running light on it goes dim then bright and repeats this.  So every time a flasher blinks thats when the taillight dims and it just keeps repeating that.
As far as the new flasher relay i read somewhere last night that you dont need a 3 prong that a 2 prong would work? not sure what the story there is? I should also note that 3 out of my 4 flasher bulbs are 6V17W and the 4th is a 6V8W bulb. I also been playing around with sanding areas for grounding with no luck. I feel like the best place to start is with the bulbs im just not sure what wattage i should be using?
Its not letting me post the link for the flasher relay i bought. This would probably be easier if i could send videos using FB messenger or get somebodies #

 

It is the bulb wattage. The more watts the slower faster they go.
(thanks automan, Its been a while since I sorted mine being too fast by getting new bulbs. Now I have checked I had 21W bulbs not 16W, that needed to also be 18W)

Google and the Yambits result thinks they should be 18W.

The flashing taillight. I think, is an earth issue.
I had dedicated cables run for my indicators to help with this.

I just tinkered with this thing for another hour and still no progress. Im going to get new bulbs that all match for starters. Ill double check into the wattage but as you said 6V18W. I have a spare taillight assembly that i plugged in to see if i would get a different result and i dont. At the time i was thinking maybe the ground wire isnt quite grounding inside the socket assembly. When i come home from work tonight i need to clean the black grounding wire that hooks to the coil under the gas tank. Bulbs and that ground wire are about all i can think of at this point. Whats bothering me is the flashers were flashing at a normal rate and all i did since then was plug in a new horn and fix my ground wire for the left rear flasher.

More wattage=faster flashing.

I checked 4 places today and nobody seems to be carrying 6V bulbs. I just ordered a 5 pack of 6v8w bulbs and a 4 pack of 6v18w bulbs. Just gotta wait for them to come in and see if 1 of the 2 combos solves my issue then its onto the blinking taillight.

Finally had time to work on the DT. Replaced all the blinker bulbs with 6v8w bulbs and that did the trick. Flashing at a normal rate. Taillight still dims a little whenever a blinker lights up. Im using a 6v18w bulb for that. Im thinking thats normal when the bike is off because of the blinker drawing power at the same time. If i just have the taillight on and hit the horn ill see the taillight go a little dimmer. Probably when the bike is running i wont see any of that.

Isn't the tail light something more like 5w, with the brake light 21w?

If I wasn't so lazy at this time in the morning then I'd look it up! 

In my parts book tailight bulb is listed as 5.3 w / 18 w

I gather ya not using the 18 for the tail light but for the brake light?, otherwise that alone could give the battery hell with the blinkers going if tail is wired that way. Probably just me reading wrong meaning into it.
Back years ago we got away with 10/3watt brake/tail to give the battery & blinkers a chance.
Std might've been 21/5.
Sorry Swoop--just read yours. You'd be right for sure.
Be good if we had regulators back in those days & could go lower wattage on everything AC & still have bright lights save from blowing & have plenty of ac volts left over to rectify to dc to keep the poor little battery up.
We even had a diode thingy that wired into the tail light circuit on say an mx bike converting to the road or enduro that used a simple system where a diode reduced the AC power to the tail light & when stepping on the brake it bypassed the diode & gave full voltage. Think that's how it worked, but ya would get past first base with something like that these days. Be illegal i'd say.

My mistake im actually using a 6v21w/5w for the taillight my bad. I ordered the bulbs by using the part number.