Installing a Relay in the Tail/Running Lamp Circuit
10-27-2009, 12:08 PM
#1
DTR's Night Watchman & Poet Laureate
Thread Starter
Installing a Relay in the Tail/Running Lamp Circuit
OK, we’re gonna install a relay in the wiring for the running lights and marker lights to take the load off the headlight switch and hopefully prevent it from melting! This will also place your trailer lights on the relayed circuit if they are wired into the running lights as most are.
Ok to start we disconnect the positive battery cable to keep from accidentally shorting anything out. I also pulled the fuse for the running lights and would highly recommend this, once you attach power to the relay, the wiring will be “hot” otherwise.
Next we remove the dash face, this is covered in a couple other write ups, so wont go into it here. After the dash front is off, you’ll see a second face-plate covering the headlight switch. To remove it you must first remove the pull-handle for the headlights. To do this,
Reach up under the dash and find the headlight switch. A little trick to give you more room for this is to depress the parking brake pedal all the way and reach up between the sidewall and hood release latch.
On the bottom of the switch is a small button that has a spring under it, this must be pushed in to release the headlight pull handle. Once the handle is out, remove the 3 screws holding the cover plate on and remove it.
Once this is off, you’ll see a round opening where the handle used to be, this is actually a stud that holds the switch in place, you can unscrew it by placing a Phillips head screwdriver into it.
Once it is out, the headlight switch assembly can be pulled out down by the parking brake pedal.
It will look somewhat like this,depending on how badly melted it is! You can see that the plug is completely melted out around the wires below my fingers. I fixed this by attaching female disconnects to the wires, passing them through the melted plug to keep them organized and in place and connecting them to the switch’s blades.
The wire resting on my finger in the photo is L7, black with a yellow trace, 18 gauge. This is the wire that feeds the running lamps and marker lamps and is the one we will splice into.
By carefully removing any sheathing over the wire bundle, you should be able to pull enough wire down to be able to work without laying on your back!
OK, go a few inches above the wiring plug and cut the wire, install a weather-tite crimp-on female disconnect onto both ends.
Since the circuit is a 30 amp circuit, I chose a 4 pole 40 amp relay sold at O’Reilly’s for aux lamps and fog lights. Instructions for which blade to attach the wires to is on the relay packaging. This photo shows the relay installed in the L7 circuit.
Next I used 12 gauge wire, about 10 foot if it and ran it through the firewall and to the positive terminal of the battery. On the inside end, I attached another female disconnect and attached it to the power supply blade on the relay.
ON EDIT: I failed to point out the importance of placing an inline fuse in this power supply!!! Thank you ppiggppenn for seeing that!
I made a short pigtail with a disconnect on one end and a ring connector on the other for a ground wire, about 8 inches long and attached it to the remaining blade of the relay. I grounded the relay to the support that holds the brake release and hood release handles at the base of the dash after reinstalling the switch.
I then taped the wiring bundle back together, taping the relays “hanger” to the wiring bundle and shoved it all back up under the dash, ensuring that the wires were clear of the parking brake.
This shows the completed wire bundle with relay:
Temporarily replace the headlight switch handle and test the install.. then remove the handle and replace the switch, cover-plate, and dash face…Viola’ we done!
It made huge difference in the light output of the side marker and clearance lights!
This also placed my trailer lights on the relayed circuit since I have the trailer lights fed off the tail lamp harness. Larger pictures can be viewed at :
http://s320.photobucket.com/albums/n...lay%20install/
HOPE THIS HELPS!!
Chris
Ok to start we disconnect the positive battery cable to keep from accidentally shorting anything out. I also pulled the fuse for the running lights and would highly recommend this, once you attach power to the relay, the wiring will be “hot” otherwise.
Next we remove the dash face, this is covered in a couple other write ups, so wont go into it here. After the dash front is off, you’ll see a second face-plate covering the headlight switch. To remove it you must first remove the pull-handle for the headlights. To do this,
Reach up under the dash and find the headlight switch. A little trick to give you more room for this is to depress the parking brake pedal all the way and reach up between the sidewall and hood release latch.
On the bottom of the switch is a small button that has a spring under it, this must be pushed in to release the headlight pull handle. Once the handle is out, remove the 3 screws holding the cover plate on and remove it.
Once this is off, you’ll see a round opening where the handle used to be, this is actually a stud that holds the switch in place, you can unscrew it by placing a Phillips head screwdriver into it.
Once it is out, the headlight switch assembly can be pulled out down by the parking brake pedal.
It will look somewhat like this,depending on how badly melted it is! You can see that the plug is completely melted out around the wires below my fingers. I fixed this by attaching female disconnects to the wires, passing them through the melted plug to keep them organized and in place and connecting them to the switch’s blades.
The wire resting on my finger in the photo is L7, black with a yellow trace, 18 gauge. This is the wire that feeds the running lamps and marker lamps and is the one we will splice into.
By carefully removing any sheathing over the wire bundle, you should be able to pull enough wire down to be able to work without laying on your back!
OK, go a few inches above the wiring plug and cut the wire, install a weather-tite crimp-on female disconnect onto both ends.
Since the circuit is a 30 amp circuit, I chose a 4 pole 40 amp relay sold at O’Reilly’s for aux lamps and fog lights. Instructions for which blade to attach the wires to is on the relay packaging. This photo shows the relay installed in the L7 circuit.
Next I used 12 gauge wire, about 10 foot if it and ran it through the firewall and to the positive terminal of the battery. On the inside end, I attached another female disconnect and attached it to the power supply blade on the relay.
ON EDIT: I failed to point out the importance of placing an inline fuse in this power supply!!! Thank you ppiggppenn for seeing that!
I made a short pigtail with a disconnect on one end and a ring connector on the other for a ground wire, about 8 inches long and attached it to the remaining blade of the relay. I grounded the relay to the support that holds the brake release and hood release handles at the base of the dash after reinstalling the switch.
I then taped the wiring bundle back together, taping the relays “hanger” to the wiring bundle and shoved it all back up under the dash, ensuring that the wires were clear of the parking brake.
This shows the completed wire bundle with relay:
Temporarily replace the headlight switch handle and test the install.. then remove the handle and replace the switch, cover-plate, and dash face…Viola’ we done!
It made huge difference in the light output of the side marker and clearance lights!
This also placed my trailer lights on the relayed circuit since I have the trailer lights fed off the tail lamp harness. Larger pictures can be viewed at :
http://s320.photobucket.com/albums/n...lay%20install/
HOPE THIS HELPS!!
Chris
10-27-2009, 08:14 PM
#3
Administrator
OK, we’re gonna install a relay in the wiring for the running lights and marker lights to take the load off the headlight switch and hopefully prevent it from melting! This will also place your trailer lights on the relayed circuit if they are wired into the running lights as most are.
Ok to start we disconnect the positive battery cable to keep from accidentally shorting anything out. I also pulled the fuse for the running lights and would highly recommend this, once you attach power to the relay, the wiring will be “hot” otherwise.
Next we remove the dash face, this is covered in a couple other write ups, so wont go into it here. After the dash front is off, you’ll see a second face-plate covering the headlight switch. To remove it you must first remove the pull-handle for the headlights. To do this,
Reach up under the dash and find the headlight switch. A little trick to give you more room for this is to depress the parking brake pedal all the way and reach up between the sidewall and hood release latch.
On the bottom of the switch is a small button that has a spring under it, this must be pushed in to release the headlight pull handle. Once the handle is out, remove the 3 screws holding the cover plate on and remove it.
Once this is off, you’ll see a round opening where the handle used to be, this is actually a stud that holds the switch in place, you can unscrew it by placing a Phillips head screwdriver into it.
Once it is out, the headlight switch assembly can be pulled out down by the parking brake pedal.
It will look somewhat like this,depending on how badly melted it is! You can see that the plug is completely melted out around the wires below my fingers. I fixed this by attaching female disconnects to the wires, passing them through the melted plug to keep them organized and in place and connecting them to the switch’s blades.
The wire resting on my finger in the photo is L7, black with a yellow trace, 18 gauge. This is the wire that feeds the running lamps and marker lamps and is the one we will splice into.
By carefully removing any sheathing over the wire bundle, you should be able to pull enough wire down to be able to work without laying on your back!
OK, go a few inches above the wiring plug and cut the wire, install a weather-tite crimp-on female disconnect onto both ends.
Since the circuit is a 30 amp circuit, I chose a 4 pole 40 amp relay sold at O’Reilly’s for aux lamps and fog lights. Instructions for which blade to attach the wires to is on the relay packaging. This photo shows the relay installed in the L7 circuit.
Next I used 12 gauge wire, about 10 foot if it and ran it through the firewall and to the positive terminal of the battery. On the inside end, I attached another female disconnect and attached it to the power supply blade on the relay. I made a short pigtail with a disconnect on one end and a ring connector on the other for a ground wire, about 8 inches long and attached it to the remaining blade of the relay. I grounded the relay to the support that holds the brake release and hood release handles at the base of the dash after reinstalling the switch.
I then taped the wiring bundle back together, taping the relays “hanger” to the wiring bundle and shoved it all back up under the dash, ensuring that the wires were clear of the parking brake.
This shows the completed wire bundle with relay:
Temporarily replace the headlight switch handle and test the install.. then remove the handle and replace the switch, cover-plate, and dash face…Viola’ we done!
It made huge difference in the light output of the side marker and clearance lights!
This also placed my trailer lights on the relayed circuit since I have the trailer lights fed off the tail lamp harness. Larger pictures can be viewed at :
http://s320.photobucket.com/albums/n...lay%20install/
HOPE THIS HELPS!!
Chris
Ok to start we disconnect the positive battery cable to keep from accidentally shorting anything out. I also pulled the fuse for the running lights and would highly recommend this, once you attach power to the relay, the wiring will be “hot” otherwise.
Next we remove the dash face, this is covered in a couple other write ups, so wont go into it here. After the dash front is off, you’ll see a second face-plate covering the headlight switch. To remove it you must first remove the pull-handle for the headlights. To do this,
Reach up under the dash and find the headlight switch. A little trick to give you more room for this is to depress the parking brake pedal all the way and reach up between the sidewall and hood release latch.
On the bottom of the switch is a small button that has a spring under it, this must be pushed in to release the headlight pull handle. Once the handle is out, remove the 3 screws holding the cover plate on and remove it.
Once this is off, you’ll see a round opening where the handle used to be, this is actually a stud that holds the switch in place, you can unscrew it by placing a Phillips head screwdriver into it.
Once it is out, the headlight switch assembly can be pulled out down by the parking brake pedal.
It will look somewhat like this,depending on how badly melted it is! You can see that the plug is completely melted out around the wires below my fingers. I fixed this by attaching female disconnects to the wires, passing them through the melted plug to keep them organized and in place and connecting them to the switch’s blades.
The wire resting on my finger in the photo is L7, black with a yellow trace, 18 gauge. This is the wire that feeds the running lamps and marker lamps and is the one we will splice into.
By carefully removing any sheathing over the wire bundle, you should be able to pull enough wire down to be able to work without laying on your back!
OK, go a few inches above the wiring plug and cut the wire, install a weather-tite crimp-on female disconnect onto both ends.
Since the circuit is a 30 amp circuit, I chose a 4 pole 40 amp relay sold at O’Reilly’s for aux lamps and fog lights. Instructions for which blade to attach the wires to is on the relay packaging. This photo shows the relay installed in the L7 circuit.
Next I used 12 gauge wire, about 10 foot if it and ran it through the firewall and to the positive terminal of the battery. On the inside end, I attached another female disconnect and attached it to the power supply blade on the relay. I made a short pigtail with a disconnect on one end and a ring connector on the other for a ground wire, about 8 inches long and attached it to the remaining blade of the relay. I grounded the relay to the support that holds the brake release and hood release handles at the base of the dash after reinstalling the switch.
I then taped the wiring bundle back together, taping the relays “hanger” to the wiring bundle and shoved it all back up under the dash, ensuring that the wires were clear of the parking brake.
This shows the completed wire bundle with relay:
Temporarily replace the headlight switch handle and test the install.. then remove the handle and replace the switch, cover-plate, and dash face…Viola’ we done!
It made huge difference in the light output of the side marker and clearance lights!
This also placed my trailer lights on the relayed circuit since I have the trailer lights fed off the tail lamp harness. Larger pictures can be viewed at :
http://s320.photobucket.com/albums/n...lay%20install/
HOPE THIS HELPS!!
Chris
A little addition that I incorporated into mine is which ever relay coil terminal you used for ground either #85 or #86 connect it in series through a spring loaded Normally-Closed toggle switch and then to ground and mount the toggle high up on the left side between your dash and the door so when you press down it breaks the circuit.
This now gives you half of an "ICC FLASH" which enables you to flash all of your marker and trailer lights as required by all big rigs.
I am using a spring loaded center off SPDT so an upwards pull will flash my headlamps.
Again looks good.
Jim
10-27-2009, 08:37 PM
#5
Registered User
Ditto ofcmarc on the "todo" list. I didn't see where you protected the "12 gauge wire, about 10 foot if it and ran it through the firewall and to the positive terminal of the battery" power wire with a fuse. Did I miss it? I like your idea of running the wires thru the melted block terminal to keep track of where they go on the switch side. That's the part that's held me back this long (about four years
). Is this a sticky yet? 
). Is this a sticky yet?
10-27-2009, 10:53 PM
#6
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Chrisreyn - For some time I have been planning putting all my headlights as well as my trailer lights on a relay, but this has me rethinking it.
I currently have a pair of relay/power distribution boxes out of some mid nineties Crown Vic police cruisers. I have doing an internal debate with myself on if I should take the signal from the switch or elsewhere. I think I will take my signal from the switch for the headlights and running lights.
Jim, thanks for the suggestion on the switch to flash the running lights. that will be a nice addition to what I plan.
Thanks - I think this helped polish the plan off. I will post my version when complete sometime in the next few weeks.
I currently have a pair of relay/power distribution boxes out of some mid nineties Crown Vic police cruisers. I have doing an internal debate with myself on if I should take the signal from the switch or elsewhere. I think I will take my signal from the switch for the headlights and running lights.
Jim, thanks for the suggestion on the switch to flash the running lights. that will be a nice addition to what I plan.
Thanks - I think this helped polish the plan off. I will post my version when complete sometime in the next few weeks.
10-28-2009, 07:55 AM
#7
DTR's Night Watchman & Poet Laureate
Thread Starter
Jim, I like that idea!! I hadn't thought of that, but it would be easy enough to add into this, guess I got my next rainy day project...
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10-28-2009, 10:02 AM
#8
Registered User
Always Always Always put a protection device on any wire coming from your battery, if it shorts out it has full battery power to melt and create hate and discontent. Very cheap insurance not to burn your rig down. As close to the battery as possible.
Mike
Mike
10-28-2009, 10:29 AM
#9
Registered User
I looked at this again, and if you powered your relay as: "Next I used 12 gauge wire, about 10 foot if it and ran it through the firewall and to the positive terminal of the battery. On the inside end, I attached another female disconnect and attached it to the power supply blade on the relay" , ... then the 12 gauge 10' wire is powering the circuit, leaving the relay signal wire fused by the oem fuse. In any case I'd be cautious of a wire coming off the battery without a fuse near the bty+ post (don't ask me how I learned that).
10-29-2009, 06:55 AM
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I burnt my plug and switch up the other day. After scrounging the wrecking yards I have found none that are good. They have either ben robbed or they are burnt. Is there any place to get a new headlight switch factory plug with pigtails? Being a royal pain to pull out of a wrecked vehicle then finding they are burnt too is enough to make you say bad words. Help please if there is such a place to get them.
10-29-2009, 08:08 AM
#11
DTR's Night Watchman & Poet Laureate
Thread Starter
I couldnt find one RCS, thats why I didnt replace mine but just put disconnects on the wires and plugged them to the switches blades. 
10-29-2009, 08:10 AM
#12
DTR's Night Watchman & Poet Laureate
Thread Starter
I looked at this again, and if you powered your relay as: "Next I used 12 gauge wire, about 10 foot if it and ran it through the firewall and to the positive terminal of the battery. On the inside end, I attached another female disconnect and attached it to the power supply blade on the relay" , ... then the 12 gauge 10' wire is powering the circuit, leaving the relay signal wire fused by the oem fuse. In any case I'd be cautious of a wire coming off the battery without a fuse near the bty+ post (don't ask me how I learned that).
-my original post edited to include this!
10-29-2009, 10:22 AM
#13
Registered User
Now if I could just get off my butt and go find my new H/L switch, .... glad you mentioned the possibility of pulling enough harness down to work with me right-side up. Looking up the rear of a dusty old dashboard isn't my idea of fun.
10-29-2009, 01:33 PM
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If I remember right the O.E. part was $25, one jobber was $30, and the local Napa was $55...... it happens every now and then.