Rockfrog Posted January 16, 2016 Share Posted January 16, 2016 Has anyone ever tried using a relay to reroute power to the blower motor? As in before that damn brown wire lights things on fire? I can see I'm walking a fine line as is right now and thought it might work. Link to comment Share on other sites More sharing options...
cruiser54 Posted January 16, 2016 Share Posted January 16, 2016 It should work. Link to comment Share on other sites More sharing options...
HOrnbrod Posted January 16, 2016 Share Posted January 16, 2016 Sure it will work - good idea too. A standard 30A relay will work just fine. EDIT: It looks like Chrysler started using a blower motor relay on the 1994 XJs and up. 93 and below had no relay. The relay coil is triggered by ignition-switched 12V and the load contacts are tied to the blower hot lead. I'm going to do this......... Link to comment Share on other sites More sharing options...
Marine1Texas Posted January 16, 2016 Share Posted January 16, 2016 Relays are awesome thing you can use to lighten load on electric system. I use two relays for my head lights that connect direct to battery then the switch from head light turn trips the relay on. I do use one for the fan blower, 12 volt utility connection and one that will allow me to turn electric fan on by switch with out a/c clutch engaging. Link to comment Share on other sites More sharing options...
NorthWoods Posted January 17, 2016 Share Posted January 17, 2016 I wish the previous owner of my truck was a little bit brighter and atleast kept all of the factory relays in place instead of hard wiring 6 circuits directly to the battery. I am in the process of rewiring the entire truck and will be adding relays for the blower motor as well as one for the electric fan I will be running. I am a huge believer in lightning the load of your electrical system. Link to comment Share on other sites More sharing options...
Eagle Posted January 17, 2016 Share Posted January 17, 2016 I wish the previous owner of my truck was a little bit brighter and atleast kept all of the factory relays in place instead of hard wiring 6 circuits directly to the battery. I am in the process of rewiring the entire truck and will be adding relays for the blower motor as well as one for the electric fan I will be running. I am a huge believer in lightning the load of your electrical system. Relays don't lighten the load on the electrical system. Ultimately, whatever component you're switching uses however much current and power as it needs. What relays do is reduce the current through the switch(es), and if properly located they also reduce voltage drop. Link to comment Share on other sites More sharing options...
Marine1Texas Posted January 17, 2016 Share Posted January 17, 2016 Agreed the battery and the alternator still have to support the power requirement. However with Relay's you can lighten the load to the switch's and the under engineered electrical system like with my 2 renix jeeps. The Grounding system is not great at all. I also notice extreme loads on positive wires and undersize wires as well. Keeping things simple with a relay setup is also required, because as you try to lessen the load thru a bad designed electrical system, you increase the amount of remembering where everything go's to. As Eagle stated Voltage drop! With volt drop you will then require higher amps to keep up, this puts strain on the light weight wiring. So with high amps items like, fans, blowers, headlights, 12 volt accessories plug, and even a high output radio, relays are key.... Link to comment Share on other sites More sharing options...
NorthWoods Posted January 17, 2016 Share Posted January 17, 2016 I don't know that I worded my response correctly but reducing current through your switches is what I would consider lightening your load. I understand that you are still going to draw the same amount of volts no matter what, as long as your system is able to produce it. I guess its better not to confuse people with my way of thinking. Link to comment Share on other sites More sharing options...
relyt120 Posted February 6, 2016 Share Posted February 6, 2016 Any further details on how to re-wire this? My switch has been scorched and my connector has been melted. When I replace them I will want to do this so it doesn't happen again. Edit: I guess my question is what to do with the brown wire and where to wire in the relay. From the diagram it looks like: 30- Const 12v 86- Switched 12v 87- To blower motor(brown wire?) 85- Ground I'm not experienced with these diagrams but this is what I could glean. Does it look right? Sure it will work - good idea too. A standard 30A relay will work just fine. EDIT: It looks like Chrysler started using a blower motor relay on the 1994 XJs and up. 93 and below had no relay. The relay coil is triggered by ignition-switched 12V and the load contacts are tied to the blower hot lead. I'm going to do this......... Link to comment Share on other sites More sharing options...
Eagle Posted February 6, 2016 Share Posted February 6, 2016 If you want to use relays, you will need four relays. In essence, there are four circuits feeding the blower motor. They go through a multi-position switch, but each position represents a separate circuit. Three of the four go through resistors, the high-speed position skips the resistors and delivers the full system voltage to the blower motor. To wire it with relays, you will need four relays, each with a fused lead to a 12-volt power source that's fed through the ignition switch. The output from each relay will then go to one of the four circuits feeding the blower motor -- three to the resistor inputs, and one directly to the blower motor. The outputs from the four positions on the dash switch will be wired to the control side of each relay. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 6, 2016 Share Posted February 6, 2016 Your wire colors won't be the same as the diagram. The blower motor relay should be wired like any load relay, and you will need a wiring diagram specific to your year/model to ID the wires. The relay coil contacts, pins 85 and 86, should be wired in series with an IGNITION SWITCHED source. Then the blower "hot" wire should be cut and wired in series with the relay load contacts, pins 30 and 87. EDIT: Just read Eagle's post. If the relay load contacts are wired in series with the motor hot input wire (Pin A in the diagram), the resistor pack outputs will still be protected by the relay since all they do is insert resistance in the ground path to vary the blower motor speed. Link to comment Share on other sites More sharing options...
relyt120 Posted February 6, 2016 Share Posted February 6, 2016 I'll have to find a diagram in my manuals. Guess it won't be as easy as wiring in one quick and neat relay. Also upon checking the scorching and melted connector are around the white with blk tracer wire on my 89. Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 6, 2016 Share Posted February 6, 2016 I'll have to find a diagram in my manuals. Guess it won't be as easy as wiring in one quick and neat relay. Also upon checking the scorching and melted connector are around the white with blk tracer wire on my 89. All you need is one relay, just like the diagram. Link to comment Share on other sites More sharing options...
Rockfrog Posted February 6, 2016 Author Share Posted February 6, 2016 Just try to minic the later (94+) pattern ... Adding a relay to the mains in should work fine the way I see it, 4 is overkill and more than ever came from the factory. I've never had the issue with me 00 XJ and it only has the one relay. The reason I originally asked was I wanted to move some load off that cursed brown wire. Link to comment Share on other sites More sharing options...
Gene Posted February 6, 2016 Share Posted February 6, 2016 Hi everyone, I may be totally wrong on this, but when I look at the wiring diagram to the MJ, it looks like you have hot from the ignition switch coming into the blower switch, to resistors, to blower motor, then to ground. So the switch and resistors are on the hot side. The XJ wiring diagram above appears to show hot, going to the relay, going to blower motor, then the switch and resistors are on the ground side. If that is right, anything done on an MJ would not be exactly mimicking an XJ. However, the principle is still the same. You still could use one relay on an MJ, going from battery to new fuse to new relay, then from relay over to connection A on the wiring diagram. The relay would be triggered by "ignition on" lead. Sound right? Gene Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 6, 2016 Share Posted February 6, 2016 ^^ Yep, you are correct. I never looked at my 91 wiring diagram, just ASSumed the motor and it's associated speed control circuitry was wired the same as the above drawing. It's not. Good catch Gene. :cheers: Link to comment Share on other sites More sharing options...
Rockfrog Posted February 6, 2016 Author Share Posted February 6, 2016 My plan is to cut the brown lead prior to the switch and wire the relay in there. So the brown wire becomes the signal only as far as the blower is concerned, then a new fused wire from battery to blower switch, with a heavier Guage. Should help some as there should be less resistance in the new wire and not having all the other circuits on the same lead. I see the old wiring and multiple heavy draw circuits as the root of all evil here. Link to comment Share on other sites More sharing options...
Gene Posted February 6, 2016 Share Posted February 6, 2016 Hi Rockfrog, Sounds like a plan! Where will you be bringing the new wire through the firewall? Are you using 10 gauge wire? Thanks. Gene. Link to comment Share on other sites More sharing options...
Eagle Posted February 7, 2016 Share Posted February 7, 2016 What year MJ are we discussing? The wiring diagrams above are for the 1997-2001 XJ. The older XJs and MJs didn't put the resistor pack in the ground leg, downstream of the blower motor. It was upstream, on the supply side, and the blower motor connected directly to ground. I suppose you could put a single relay between the resistor pack and the blower motor input, but then the heater switch would still be carrying the load of the resistor pack. Putting multiple relays upstream of the resistor pack takes all significant load off the blower switch -- all it would be carrying is the load of a single relay control side. Link to comment Share on other sites More sharing options...
cruiser54 Posted February 8, 2016 Share Posted February 8, 2016 Don't forget to do this along the way. http://cruiser54.com/?p=211 Link to comment Share on other sites More sharing options...
Rockfrog Posted February 8, 2016 Author Share Posted February 8, 2016 To go back, yeah, was thinking a 10ga supply lead through the firewall. As for the relay, I see it as the switch is getting the short end of the stick, as all the other high draw circuits leave little voltage available for the blower ... Thus the draw goes up due to increases resistance. By adding the relay ahead of the switch, I cut all those out and the blower will see full voltage again. And as a result of lower existence in the circuit ... The switch should see longer lifespans. Even with a new alternator in the mix (100A). I am still seeing the usual draw down to nearly 9V when driving at night with the heat on and the wipers going. Pretty standard stuff for a Renix. Cruiser - did that one last week. And have a 1990 harness to swap out one day to Eliminate my C101 (the last tip that needs doing). Love my Renix, she runs like a top, and gives me few issues, even with a warped exhaust manifold and worn rings. Gotta fix that eventually too. But she just keeps going. Link to comment Share on other sites More sharing options...
Eagle Posted February 8, 2016 Share Posted February 8, 2016 How will adding a relay ahead of the switch reduce the current flowing through the switch? Link to comment Share on other sites More sharing options...
Rockfrog Posted February 8, 2016 Author Share Posted February 8, 2016 By increasing the available voltage, to a full 12V instead of the 10V remaining after all the excess draw due to multiple circuits drawing from one lead. And instead of having the supply feed take to long drawn out route I can wire it direct (read - shorter run on wire). More available Voltage means less Amperage draw no? Link to comment Share on other sites More sharing options...
HOrnbrod Posted February 8, 2016 Share Posted February 8, 2016 Yep. Ohm's law says so. The load (watts) will remain constant. A load of 100W with a 12V supply will draw 8.3 amps. The same load with a 10V supply will require 10.0 amps. Larger wire cross sectional size and a shorter run will decrease resistance and drop the required amps even more. :smart: Link to comment Share on other sites More sharing options...
Eagle Posted February 8, 2016 Share Posted February 8, 2016 So what's going to control the relay? Wouldn't it be easier to accomplish the same thing just by running a larger wire to the input side of the switch? Link to comment Share on other sites More sharing options...
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