Diode question for additional dome lamp

[cadfan64]

Here's a question for the electrical gurus. I will be installing a second dome/map lamp in the rear of my car while I recover the coach roof interior trim and have the back glass tinted. I will be making up a harness to be snaked under the headliner to the original lamp for the power and grounds for the dome lamp (circuit 53 EVTM) and the map lights (circuit 54). I am also going to install a switch in the rear passenger area to turn on the rear dome lamp only. I know I need to put a diode in the harness in circuit 53 between the new and original lamps, very much like is illustrated on page 72 of the EVTM for the wagon cargo light, to keep the power from back feeding to the other courtesy lights.

My question is, what "size" diode do I need. A part number /source would be very helpful. Is there an easy way to determine which way the diode needs to be installed?

In case you are wondering why I am using the extra switch when the map lights can be turned on separately? Because I WANT to :lol:

Thanks for any and all help!

[Danny_R]

You shouldn't need diodes for this. I have yet to look at the connections on the dome/map lights but if I were you I'd run 3 wires from the existing dome light to the rear dome/map light. One of the wires will come from the existing map lights which will be hot all the time and will run your map lights on the rear one, second wire will be from the existing dome lamp (middle bulb) to a single pole switch (wherever you decide to mount it) and then a wire from the switch to the dome lamp (middle bulb) in the rear. Your third wire will be a common ground. So, when the switch for the rear lights is in the ON position, the dome lamps will illuminate with the doors or the dome light override switch. Turn the switch to off and only the front dome will work. The map lights will function independently regardless of which position the switch is in.

If you need a diagram let me know.

Danny

[GoodSamaritan]

DIODES 101


If you put the side with the stripe toward ground, current will flow.
In other words, if you want the rear light to come on with the dome, but not the other way around, you'd put the side with the stripe toward the rear light.
Then put the power from the switch into the circuit between the diode and the rear light.

As for size? I'd go to radio shack and pick up a pack of "rectifier diodes" One of the big ones that's 1/4-5/16" of an inch in diameter should be fine. Or else get a pack of the smaller ones, turn them all so they are oriented the same way and hook them all up together in a bundle, (side by side, not end to end)


If you have any more questions let me know via pm, and I'll draw it out for you.