Yes, you test the diode by setting the meter to resistance.

The diodes have two pins on them. put one probe of the meter on each pin of the diode, see what the reading is. Then swap the position of the probes of the meter and see what the resistance is. One way should be alot lower than the other way.

When you take the diode out make sure that you pay attention to which way it was installed. If you install it the wrong way it will not allow the circuit to work properly. Unless the two pins of the diode are differnt so its impossible to put it in wrong. (Like how relays are they have one pin that is sideways compared to the others so there is no way it can go in wrong)

The diodes will probably cost somewhere between $2 and $3 each. I want to say that they are standardized like the fuses so they should be reasonably easy to find. If you do get new ones make sure you take the ones you are replacing with you to make sure that you get the right ones.

If you try the DO NOT TRY THIS way of testing the starter by shourting the pins I mentioned it won't matter if the clutch is pressed or not for it to work. Thats why its dangerous. If all the wiring is good The engine will crank wether the transmission is in gear or not and the clutch out or in. So when the engine turns the car can move and if it starts it will drive away without out you or if you're in front of it, it will drive over you. Thats why its dangerous.

If the small wire has a resistance under 1, then that means that either R6, the starter, the ignition diode, the starter diode or the big wire from the battery to the starter are bad.

To test the big wire, disconnect it from the starter and from the battery and check the resistance trough it. You should see 1ohm or less, even go as far as to push and twist the probe into the end of the wire that attaches to the battery so it digs in a little to be sure it gets a real good connection you're looking for 1ohm or less.

To test R6.
take it out. Connect (-) 12 volt power to pin 1, connect (+) 12 volt power to pin 2. Make sure you connect power to the pins of the relay by some means that can hold themselves on becasue you'll need your hands free to hold the probes of the meter. AS soon as you make that connection you should hear and or feel the relay click. Then use your resistance meter and test the resistance between pins 3 and 5. (it doesn't matter which probe of the meter you touch to the pins as long as one probe is on 3 and the other probe is on 5) the resistance should be low. If its high or infinity its bad. If you just want to replace it R6 will proably cost in the area of $6 to $10.

I feel sorry for the people who don't drink. When they wake up in the morning, thats the best they're going to feel all day - former President Lyndon B. Johnson