I have a Whirlpool dishwasher in my shop, model number 7DU1100. The problem is that the normal light flashes continually and the user is unable to use the dishwasher.

I am not one to tell the customer that its simply the board and it needs to be replaced. I like to understand it and know for sure. I sold them the dishwasher 4 years ago and I can attest that they probably only used it less than a dozen times in that period.
Does anybody have any knowledge of these machines? Is there a way to get this to go into diagnostic mode? I tried pushing the Sani Rinse and alternating with the heated dry and this did not send it to diagnostics.

Thank you
jeep_man

The blinking normal light is the diagnostic mode and means the keypad/controller are defective. The simplest explanation is the best. It surely cannot achieve any other diagnostic function until this condition is remedied.

Many of these dishwashers were made with defective and/or weak capacitors made in Taiwan that have leaked, swelled up and shorted/opened. This is due to them using a stolen formula for Japanese capacitors filling fluids where they failed to steal the final step in the process. That is why many products made in the last 20-30 years since 1989 have failed. Here are some manuals: https://dl.dropboxusercontent.com/u/8010163/Whirlpool_Kenmore%20Dishwashers.zip
Look on YouTube to see which capacitors need replacing on your model. I fix TVs like Coby TVs which have power supplies that have failed from these bad capacitors, too. Make sure you use a polarized capacitor if the original is polarized. Use the same type, but you can use a higher voltage for more durability.

Excellent . Thank you very much!

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Make sure you use a polarized capacitor if the original is polarized. Use the same type, but you can use a higher voltage for more durability.
Don't go too much higher on the voltage, as electrolytic capacitors like to operate reasonably close to their rated voltage.
WallyH