Hi I was wondering if anyone has a wiring diagram for a honda b75 outboard engine. I have a black wire from the valve pulley, a black wire from the wiring harness below the crank pulley, a white wire

SOURCE: gear box oil leak

Here is a website where a manual for you outboard may be purchased.  Outboard Marine went out of buisness in 2000 and thus no parts of origial manufacture are support is available . Therir are secondary markets .    THe Lower case splits in half and their is a seal around the prop shiftm which is pressed in. The seal between the cases are cut o-rings which are placed and glued into place with gasket seal.
The water pump is located where the case splits a little bit higher. You must open the little port on the side and take out one of the screws to the connecting shift linkage to split the case. After splitting the case the drive shaft and water pickup tube(s) wil come out of the powwer head or the tubs may stick into the power head which is ok. Place the lower skag into a vice and remove the 4 or 5 screws to the water pump housing. Remove and replace impellor and impellor plate if available. If part(pieces) of the rubber impellor is missing flush out the tubes and the power head to remove them.   When reinstalling the lower unit use a flash light to make sure that the tubes return  to the proper place in the power head and the shift lever is resecured. If you need more assistance, just write back. I was an Outboard motor mechanic for five years about the time of your motor.  

SOURCE: turn the switch off motor keeps running

It sounds like there is a short in the alternator or wiring for alternator. You are continuing running with the battery cut off. But the outboard generates its own power and its finding the way to the ignition. As for grounding, you may be idling too high for a quick shut off.

SOURCE: Looking for a starter solenoid wiring diagram

save yourself some money and go get a lawn mower solenoid and find a way to mount it yourself. I have done a johnson outboard and a tigershark jet ski this way with no problems.

SOURCE: MERCURY OUTBOARD 50HP 1974 NO SPARK

Clean or replace and set points to .020. Also replace your condenser.

SOURCE: iam looking for a wiring diagram for a 1964 40

Here is a link to the diagram you need.
http://www.maxrules.com/graphics/omc_pics/wiring/61_66_40HP.jpg