I wanted a power feed that was only active when the engine was actually running, so the batteries wouldn't get drained by accident. In my case, I wish to recharge my trailer battery while driving, without having to worry about killing the batteries.
For this purpose, the red wire on the rear 7way plug and in the 5th wheel harness are the 12v battery wires. These wires are connected together and get their feed from "stud 1" in the under hood fuse box. This wire is protected by a 40A fuse in the box. You have to remove the fuse box cover to access this stud, then it will be at the upper left corner. It is referenced in the diagram attached to the underside of the fuse box lid. There may be other wires attached to the stud, if so, make sure you select the proper one. I cut this wire, and extended it so both ends were long enough to reach the relay mounting area I chose. The power wire from the stud attached to terminal #30 and #86 on the relay, the other half of the wire from the harness attaches to terminal #87.
This setup could be used for many other applications, like air compressors, inverters, etc. You can also use the output from terminal 87 to control one or more other relays, which also have switches that go to ground to activate. This way you can use a second relay to control, say, an air compressor. The air compressor pressure switch can be attached to terminal 87 on the 2nd relay, the other end of the switch would go to ground. When the air pressure gets low enough, the compressor would turn on IF the engine were also running, otherwise the relay would not have control power and would not energize.
The switch I used was a GM/Delco part D1811 or 10002798. I believe it was used to control a fuel pump originally. Cole Hersee also makes suitable switches. The key is, the switch should be OFF normally, and turn ON with rising pressure.
The relay I used was a Bosch unit, part number 0 332 014 157. This relay is normally OPEN, and closes when current is applied to the control coil.
Some similar relays have both NO and NC contacts, these will work fine also, just choose the NO contacts for this setup.
The normal place to attach this switch would be to T into the oil pressure sender. However, the sender is in a tight area, and you would probably have to space out the two switches quite a bit to install a nipple and T fitting. I didn't like this idea, with the vibration of the diesel, it is possible for the pipe nipple to snap off over time. So I attached the new switch to the engine oil filter adapter/cooler housing. See photos for the switch location, as there are several different plugs. I think some of them control a bypass function, and I didn't want to mess with them.
The one I used has some sort of metal down inside the port, but it didn't come out, and didn't see to be affected by the plug I took out. At any rate, it works. The plug I removed had a recessed allen bore, and was 1/4 NPT (pipe thread). The oil pressure switch is 1/8 NPT.
So you need to pick up a 1/8 female by 1/4 male adapter from the auto parts store. I had a brass 1/4 NPT hex plug handy, so I drilled it and tapped it for the 1/8 NPT so the switch would fit. There are reducer bushings that you can buy that are almost exactly what I used.
At any rate, remove the plug from the oil filter adapter as shown. Then install the adapter Use plenty of teflon tape to seal the adapter, but make sure not to get any into the hole.
Next, install the oil pressure switch. The one I used had pre-applied sealant, so I just cranked it into the adapter. Make sure both pieces are tight, but don't get medieval.
The switch has two terminals that close when the switch senses pressure. One terminal should be grounded with a wire. You can attach this wire to the chassis or body, as long as it has a good connection. The other wire will be routed to your relay location and attach to terminal #85.
I located my relay right next to the underhood fuse box, so that's where I ran the wire to. I would suggest sleeving the wire with plastic loom cover, and secure it with zip ties.
Notice that the power feed supplies two terminals, #30 which is the power feed for the relay, and #86, which provides a very small amount of power for the relay coil. Although the relay has power to the coil all the time, the relay will not operate until the terminal #85 becomes a ground.
Hope this info is helpful.
Thanks,
Bryan
For this purpose, the red wire on the rear 7way plug and in the 5th wheel harness are the 12v battery wires. These wires are connected together and get their feed from "stud 1" in the under hood fuse box. This wire is protected by a 40A fuse in the box. You have to remove the fuse box cover to access this stud, then it will be at the upper left corner. It is referenced in the diagram attached to the underside of the fuse box lid. There may be other wires attached to the stud, if so, make sure you select the proper one. I cut this wire, and extended it so both ends were long enough to reach the relay mounting area I chose. The power wire from the stud attached to terminal #30 and #86 on the relay, the other half of the wire from the harness attaches to terminal #87.
This setup could be used for many other applications, like air compressors, inverters, etc. You can also use the output from terminal 87 to control one or more other relays, which also have switches that go to ground to activate. This way you can use a second relay to control, say, an air compressor. The air compressor pressure switch can be attached to terminal 87 on the 2nd relay, the other end of the switch would go to ground. When the air pressure gets low enough, the compressor would turn on IF the engine were also running, otherwise the relay would not have control power and would not energize.
The switch I used was a GM/Delco part D1811 or 10002798. I believe it was used to control a fuel pump originally. Cole Hersee also makes suitable switches. The key is, the switch should be OFF normally, and turn ON with rising pressure.
The relay I used was a Bosch unit, part number 0 332 014 157. This relay is normally OPEN, and closes when current is applied to the control coil.
Some similar relays have both NO and NC contacts, these will work fine also, just choose the NO contacts for this setup.
The normal place to attach this switch would be to T into the oil pressure sender. However, the sender is in a tight area, and you would probably have to space out the two switches quite a bit to install a nipple and T fitting. I didn't like this idea, with the vibration of the diesel, it is possible for the pipe nipple to snap off over time. So I attached the new switch to the engine oil filter adapter/cooler housing. See photos for the switch location, as there are several different plugs. I think some of them control a bypass function, and I didn't want to mess with them.
The one I used has some sort of metal down inside the port, but it didn't come out, and didn't see to be affected by the plug I took out. At any rate, it works. The plug I removed had a recessed allen bore, and was 1/4 NPT (pipe thread). The oil pressure switch is 1/8 NPT.
So you need to pick up a 1/8 female by 1/4 male adapter from the auto parts store. I had a brass 1/4 NPT hex plug handy, so I drilled it and tapped it for the 1/8 NPT so the switch would fit. There are reducer bushings that you can buy that are almost exactly what I used.
At any rate, remove the plug from the oil filter adapter as shown. Then install the adapter Use plenty of teflon tape to seal the adapter, but make sure not to get any into the hole.
Next, install the oil pressure switch. The one I used had pre-applied sealant, so I just cranked it into the adapter. Make sure both pieces are tight, but don't get medieval.
The switch has two terminals that close when the switch senses pressure. One terminal should be grounded with a wire. You can attach this wire to the chassis or body, as long as it has a good connection. The other wire will be routed to your relay location and attach to terminal #85.
I located my relay right next to the underhood fuse box, so that's where I ran the wire to. I would suggest sleeving the wire with plastic loom cover, and secure it with zip ties.
Notice that the power feed supplies two terminals, #30 which is the power feed for the relay, and #86, which provides a very small amount of power for the relay coil. Although the relay has power to the coil all the time, the relay will not operate until the terminal #85 becomes a ground.
Hope this info is helpful.
Thanks,
Bryan
