Installing Fog Lamps
Record Breaker
Joined: Jun 2008
Posts: 1,970
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From: Clermont, Florida
YW. If you wanted to simplify this installation you could just tap into the ignition positive wire at the steering column. It should be dark blue, about 14 gauge but check with a volt meter anyway. It's located in the wire harness leading from the ignition switch under the steering column. You could use ignition voltage and put your toggle switch inline and wire the ignition positive power as the power input to the relay. But you would not get the automatic shut down of the Bosch lights when you hit the high beams. You would have to turn them on and off manually every time which is a pain.
Now if you wanted to use ignition voltage to power the new Bosch lights and still get them to turn off with the OE fog lights, that is easy to do. But you will need 2 Bosch 30 amp relays. Wire them this way:
Relay 1: Terminal 86 to the ignition 12 volts
Terminal 87 to battery positive post, fused same as the Bosch lights
Terminal 30 is output positive voltage to the new fog lights
No connection on 87a but insulate it to avoid shorts
Relay 2: Terminal 85 to good solid ground
Terminal 86 to the 12volt positive wire on one of the OEM fog lamps
Terminal 87 to good solid ground
Terminal 30 gets connected to terminal 85 on the first relay
No connection to terminal 87a on this relay. But insulate it to avoid shorts.
What this will do is let the first relay provide power to the Bosch fog lamps when you turn on the factory fog lamp switch on the dash. When relay #2 is at rest when you hit the high beams and the OEM fog lamps turn off, the ground to relay #1 is interrupted so the Bosch fog lamps turn off. The OEM fog lamps will turn off like they always have. You can still have the toggle switch in the dash for when you want to run only the OE fog lamps. You could even find the red/orange wire at the CTM or under the dash that provides 12 volts when the high beams are on and use that as the input voltage to the second relay on its terminal 86. It's a smaller gauge wire, maybe 16 gauge and you can find it a little easier at the CTM. Be sure to use a digital volt meter and not a test light. It will have 12 volts only when the high beams are on. It will rest at ground when the high beams are off. In that case just change the ground on terminal 87 to terminal 87a on that relay and have no connection on terminal 87.
With the relays you can use any source of positive voltage you want. I wired my own aftermarket fog lights with this two-relay configuration. The positive input I used was the one from the parking lamp bulb. Again I picked it up at the parking light bulb so as not to cause any problems with the CTM. My truck did not have fog lamps from the factory. With yours you need to use ignition voltage or the voltage from the OE fog lamps, because you are adding a second set of fog lamps.
Relays are like switches but they are controlled by the electromagnetic coil inside the relay, not by a physical action like flipping a toggle switch. They are just relaxed or energized by terminals 85 and 86, which can be understood as "power" and "ground" across the electromagnetic coil. When there is power on 86 and ground on 85 (or the other way around it doesn't matter which) the relay is energized and whatever voltage you have connected to terminal 87 will be output on terminal 30. At rest, when either 85 or 86 loses its power or ground, the connection changes to terminal 87a and is still output on terminal 30. When we think of relays this way, the possibilities are endless if you need to add circuits to your truck.
Radio shack sells a nice flush mount toggle switch for 5 or 6 bucks. It fit well just below the headlamp switch in my truck but takes a pretty good size hole to mount it. If you use it make sure you drill where there's enough clearance. There is additional plastic behind that area. It's a lot easier to do this when you put the relays out under the hood. Much less wires to run into the cab and easier to service if you have a problem with it. Just wrap the relay terminals up well with electrical tape to insulate them from the elements. If you look behind your battery on the inside of the driver's side fender well you will even see 2 holes in the fender well to mount the relays to without having to drill anything. Just need a couple of screws. Wiring the fog lamps and relays is not hard but you are right in doing it on a day when you have plenty of time for it. That and having the right tools and the patience for the job will make it a fairly easy and very worthwhile addition to your Dakota.
Jimmy
Now if you wanted to use ignition voltage to power the new Bosch lights and still get them to turn off with the OE fog lights, that is easy to do. But you will need 2 Bosch 30 amp relays. Wire them this way:
Relay 1: Terminal 86 to the ignition 12 volts
Terminal 87 to battery positive post, fused same as the Bosch lights
Terminal 30 is output positive voltage to the new fog lights
No connection on 87a but insulate it to avoid shorts
Relay 2: Terminal 85 to good solid ground
Terminal 86 to the 12volt positive wire on one of the OEM fog lamps
Terminal 87 to good solid ground
Terminal 30 gets connected to terminal 85 on the first relay
No connection to terminal 87a on this relay. But insulate it to avoid shorts.
What this will do is let the first relay provide power to the Bosch fog lamps when you turn on the factory fog lamp switch on the dash. When relay #2 is at rest when you hit the high beams and the OEM fog lamps turn off, the ground to relay #1 is interrupted so the Bosch fog lamps turn off. The OEM fog lamps will turn off like they always have. You can still have the toggle switch in the dash for when you want to run only the OE fog lamps. You could even find the red/orange wire at the CTM or under the dash that provides 12 volts when the high beams are on and use that as the input voltage to the second relay on its terminal 86. It's a smaller gauge wire, maybe 16 gauge and you can find it a little easier at the CTM. Be sure to use a digital volt meter and not a test light. It will have 12 volts only when the high beams are on. It will rest at ground when the high beams are off. In that case just change the ground on terminal 87 to terminal 87a on that relay and have no connection on terminal 87.
With the relays you can use any source of positive voltage you want. I wired my own aftermarket fog lights with this two-relay configuration. The positive input I used was the one from the parking lamp bulb. Again I picked it up at the parking light bulb so as not to cause any problems with the CTM. My truck did not have fog lamps from the factory. With yours you need to use ignition voltage or the voltage from the OE fog lamps, because you are adding a second set of fog lamps.
Relays are like switches but they are controlled by the electromagnetic coil inside the relay, not by a physical action like flipping a toggle switch. They are just relaxed or energized by terminals 85 and 86, which can be understood as "power" and "ground" across the electromagnetic coil. When there is power on 86 and ground on 85 (or the other way around it doesn't matter which) the relay is energized and whatever voltage you have connected to terminal 87 will be output on terminal 30. At rest, when either 85 or 86 loses its power or ground, the connection changes to terminal 87a and is still output on terminal 30. When we think of relays this way, the possibilities are endless if you need to add circuits to your truck.
Radio shack sells a nice flush mount toggle switch for 5 or 6 bucks. It fit well just below the headlamp switch in my truck but takes a pretty good size hole to mount it. If you use it make sure you drill where there's enough clearance. There is additional plastic behind that area. It's a lot easier to do this when you put the relays out under the hood. Much less wires to run into the cab and easier to service if you have a problem with it. Just wrap the relay terminals up well with electrical tape to insulate them from the elements. If you look behind your battery on the inside of the driver's side fender well you will even see 2 holes in the fender well to mount the relays to without having to drill anything. Just need a couple of screws. Wiring the fog lamps and relays is not hard but you are right in doing it on a day when you have plenty of time for it. That and having the right tools and the patience for the job will make it a fairly easy and very worthwhile addition to your Dakota.
Jimmy
Last edited by 01SilverCC; Sep 1, 2008 at 07:40 PM.