May 17th, 2004 : Wiring Dome Light via Door Switches
I ordered a new chrome dome light from Chevy Duty -- 1-800-741-1678 Part #26-021C -- but I wanted it to operate via the door switches I installed, and there was a problem about doing that. The door switches connect and disconnect the ground for my interior lights, and the dome light has a constant ground provided by the dome body itself ... it operates by connecting and disconnecting the power wire at the dome light switch. So how could I make it turn on when I opened my doors, activating the ground from my door switches? No problem! As explained on page 20, in the manual that comes with Mad Electrical's relay kit, you can get positive output from a ground output using a relay!
If this is your first time installing relays, the kit above is the way to go - the booklet that comes with the kit explains all the different applications for relays and is a great resource to have ... but once you have all the supplies and experience, you can buy Bosch relays for about $3.50 each (like I'm now doing) via Parts Express. I just phone my orders in:
1-800-338-0531 but if you'd rather, you can order from the web site:
So, here's the deal:
Note: Instead of disconnecting my battery, as I always do whenever working with anything electrical on the truck, I just pulled the fuse for interior lights (the power wire I'd be working with) and the circuit is safe to play with.
1 - Using a power wire from my fuse box (designated for the interior lights), I wired the dome light in the usual way; sending power to the dome light at the contact before the switch. At this point, the dome light works by turning it's switch on ... the switch connects power to the bulb; the dome light body is grounded by the truck body and the light comes on.
2 - Next, using the same power wire from my fuse box (designated for the interior lights), I connected to the #86 and #30 posts on the relay (see schematic below). The #87 wire from the relay goes the bulb-side of the dome switch connection -- at the contact after the switch, and the #85 wire from the relay goes to the door switches. Now, when I open either door on my truck, the door switches turn the relay on, the relay sends power to the dome light and the light comes on.
P.S. -- You may also be interested in checking these other electrical projects out:
Mad Electrical Improvements -- [Click Here]
Wiring An Electric Fan With Two Relays -- [Click Here]
Headlight Relays -- [Click Here]
Understanding Relays -- [Click Here]
About Fusible Links -- [Click Here]