I would like to hook up a under hood lamp to my Cadillac Escalade. A TSB (Technical Service Bulliten) from Cadillac says to never connect accessories to the vehicles wiring without using a diode to protect the vehicles electronic components. My question is which type of diode to buy, and how to connect it. I saw many types of diodes available on line but am lost. Please help. Thanks a bunch....
(NOTE: I have copied this answer from the comments above. They appear to be accurate and definitely answer the question. I didn't want the question to appear as unanswered.)
For passive resistive load, I do not think the diode is needed. But if you would use a diode, you would connect your positive source voltage to the anode and your receiving equipment on the cathode side. Current would then flow to the equipment but would not be allowed to flow back to the power source. The more important components is FUSE. The function of a fuse is to protect the circuit (wiring) that it is attached to. If the wire is not fused, and the main power shorts to ground, the wire (or the car in worst case) will be burned.
The type of the diode depends on the current needed by the load (current = power divided by voltage). You can use 1N4002 for load current <1A, 1N5400 for <3A, or 1N5825 for <5A.