diode math, please help

does anyone know what happens when you put 2 diodes in series or parallel? Does the amperage change? Does the voltage change? Does the capacitance change? The answer is more than likely a yes. So how is the change calculated? Is it same as resistors or differently calculated? Any electronic engineer, genius or guru out there? please help.

Just wondering. I put 2 diodes (1N4003's) in parallel for my door trigger via domelight sense -ve. Normally they put 1 diode. My alarm does not trigger at all. Are you sure 2 diodes in parallel will result in no more voltage drop than a single diode and allow only double the current passage??

actually if the polarities were reversed, since they are in parallel, they would have no effect other than a shorted/straight wire. The reason why I used 2 was just in case one failed (cut off) the other would still let the voltage pass back through the workign one so the sensor gets its -ve sense. I have not tried with one. the weather was so cold that all my fingers and toes and myself were turning numb. Hopefully next weekend if the weather is bearable, I will check and investigate for reals with my DMM. Till then I just have to wonder. Most probably I won't even use the dome light, but the actual door triggers even thought it is going to be a pain in the but.