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  • Green wire to fan switch load rating?

    Hello,

    I’m in the process of adding dual wideband O2 sensors and an AFR gauge to my TR6. The sensors are heated, and I’ve read that the typical load during warmup is about 5.5 A.

    For convenience, I’ve got the whole system wired to the fan switch hot side, so a dark green wire that is switched and fused. I chose it because it was close to where I mounted the gauge controller, behind the center dash support, and because it was normally used to feed a high-draw item.

    For now, I’ll make sure not to turn the fan on while the sensors are warming up, but I was wondering if anyone knew what the load rating of the green wire that supplies the fan motor is? The wire that feeds the AFR system is quite thin, Is it true that the heaters really draw 5.5 A? These are 2 standard Bosch wideband O2 sensors.

    My concern is that I might overheat the wire, particularly if I turn the fan on.

    Thanks, Tom

  • #2
    As I remember from when I refurbished my wiring harness, all of the green wires are British 14 strands wire that are capable of carrying 8 Amps. According to the Dan Masters Fuse Load document that I am attaching below, the heater fan draws 4 Amps.

    In my opinion, the green wire circuits are not the best design. As already noted, all of the wires are 14 strands and many of the wires are connected with a 5 or 6 wire splice built into the harness. Problem is, on the 69 - 72 models that splice if fed by a wire from the fuse box to the brake light switch then on to the splice. Those two wires are carrying all of the green fuse load other than the single wire going to the windscreen wiper park circuit. They should have been 28 strand wire, but from all the pictures I have, they sure look like 14 strands.

    On the 73 - 76 models, a single wire feeds the splice directly from the fuse box. I don't know if they upped it to 28 strands or kept it at 14.

    Click image for larger version

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    [ATTACH]n541501[/ATTACH]
    R3
    Jim Herter,͏͏͏͏͏͏͏͏͏Copperas Cove, TX
    Original Owner ֍ 1970 TR6 CC 50990 LO

    Comment


    • #3
      Thanks Jim, that is perfect. Leave it to Triumph to design the wiring harness using the same size with for a 4A heater as for a low-draw instrument. I’ll need to find a better way to wire the sensors.

      Comment


      • #4
        I assume you are referring to the heater fan switch. Personally I would run a separate 8 gauge wire to the fuse box, switched side and not risk it. You can always tape the extra wire to the existing loom as I have done in the past so it’s not seen.

        While we are on the fan switch, wrap a few layers of electrical tape to encapsulate all the outer tabs connected or not as most are hot at one tim or another. If that switch moves a bit in its mount and one of those tabs contacts the metal dash, smoke and melted loom will happen. Seen it too many times. Make sure it’s centered and tight.
        72 Pimento w/overdrive - Lilred
        67 4A Royal Blue - Lilblue

        Comment


        • #5
          Yeah, there's enough going on with the existing wires....just run a new circuit.
          There may be a vacant fuse connection in the fuse box...if so make a jumper from the white wire to the vacant spot, insert a fuse and create a new circuit.
          Driving a 1973 TR6
          Doing ZS carb repairs
          email kencorsaw"at"aol.com

          Comment


          • #6
            Thanks Gents,

            lfmTR4 I bought a TR250 25 years ago that had that same situation. The owner told me the "heater motor is bad" because it blew the green fuse as soon as you switched it on. I lived fanless until the first winter, and was preparing to tear the dash and console apart to remove the heater box when I was pleasantly surprised to find the fan switch shorted to the metal parts. I still remember it fondly because it was the rare LBC repair that turns out to be LESS than you thought it was going to be at the outset.

            Not sure about the 8 gauge though, seems like a lot.

            poolboy I was thinking of doing just that, and while I'm at it I'll make the new circuit feed the radiator fan relay as well, so my ammeter doesn't read backward with the fan running. I currently (see what I did there?) have it wired directly to the battery.

            Thanks for the help gents.
            Last edited by TR250Tom; 04-30-2021, 07:40 AM.

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            • #7
              Originally posted by TR250Tom View Post
              Thanks Gents,

              lfmTR4 Not sure about the 8 gauge though, seems like a lot.
              Yeah I shorted out there, 8 is what I ran when I upgraded the alternator. You should be fine with 14-16 a 4A.
              72 Pimento w/overdrive - Lilred
              67 4A Royal Blue - Lilblue

              Comment


              • #8
                So how does this look? Horror Show, DPO at work, OK?

                I haven't hooked the fan and O2 sensors to the output (fused) side yet, obviously. I need some 14 gauge wire, which seems to be the one I don't have in my wiring-stuff drawer.

                I'm starting with a 15A fuse, which is what the Spal fan had all by itself, on the theory that the cooling fan and the sensor peak heating will never be happening at the same time. If it blows, I'll replace it with a 20A.

                Click image for larger version

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                Comment


                • #9
                  It looks like you took some care doing it...it's neat and clean.
                  Driving a 1973 TR6
                  Doing ZS carb repairs
                  email kencorsaw"at"aol.com

                  Comment


                  • #10
                    Thanks Ken. After thinking about it, I'll run a new green wire for the AFR sensors, but I won't relocate the radiator fan because it seems to me I'd be pulling an additional 10A through the ignition switch on the white wires. That can't be good.

                    Comment


                    • #11
                      My e-fan has been running on the keyed circuit for over 10 years and it hasn’t ever been a problem. I wanted it to be off with the key so I wired the control relay through the key and fused power to the fan directly from the alternator since it was close. Of course it rarely comes on, only with prolonged idling or extended stop and go traffic.
                      72 Pimento w/overdrive - Lilred
                      67 4A Royal Blue - Lilblue

                      Comment


                      • #12
                        Mine is also "keyed" to a relay and fuse taking the load off the ignition switch,
                        Driving a 1973 TR6
                        Doing ZS carb repairs
                        email kencorsaw"at"aol.com

                        Comment


                        • #13
                          Hmmm...Thanks for that, perhaps I should reconsider. I have the relay actuated by the switch as well, I want to control the radiator fan operation with the key.

                          Ken, you have the power feed for the fan connected to the fuse box opposite a “white” switched power supply as well? Or somewhere else?

                          lfm, are you running a Lucas alternator? How did you connect the fan directly to the alternator?

                          Thanks. I would like to get my ammeter reading correctly, but I’m afraid of smoke-checking my wiring harness just as the snow is melting up here.

                          Comment


                          • #14
                            Kinda, Tom...I get power to the relay from the temperature sensor which is connected to White wire side of a fuse in the fuse box, BUT the fan motor is powered by the battery thru the relay..My relay and fuse for the fan circuit is in the engine bay on the passenger side firewall.
                            If you open this link and then click "DOWNLOAD INSTRUCTIONS" what I did is shown in "Diagram #2" I used the green wire for a temperature sensor override switch in the cockpit....It will turn the fan on without the sensor, but it can not turn off a fan that was turned on by the temperature sensor
                            https://derale.com/product-footer/el...t-11-32-detail
                            Last edited by poolboy; 05-01-2021, 03:34 PM.
                            Driving a 1973 TR6
                            Doing ZS carb repairs
                            email kencorsaw"at"aol.com

                            Comment


                            • #15
                              OK thanks Ken. That’s exactly how I have mine wired, override switch and all. The problem is, my 1971 car has an ammeter, not a voltmeter like your ‘73. When I wire loads directly to the battery, they give erroneous charge readings. If I turn my lights on with the engine not running, the ammeter shows a battery discharge. If I turn my fan on with the motor not running, it shows nothing, because the high load to the relay is bypassing the ammeter. If I turn the fan on with the motor idling, if shows a high charge (the ammeter sees the stepped up flow to the battery, but not the even greater load leaving the battery) when it should show a discharge. That’s what I was hoping to fix.
                              Last edited by TR250Tom; 05-01-2021, 06:58 PM.

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                              Green wire to fan switch load rating?

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