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Technical 350 Runs couple seconds aftyer key turned off

Discussion in 'Traditional Hot Rods' started by Thomas Schaar, Jul 8, 2017.

  1. 24riverview
    Joined: Jan 13, 2008
    Posts: 793

    24riverview
    Member

    That would have to be a pretty big diode I would think considering the fan could draw 30-40 amps at start up.
    Changing to a constant source would fix the run on but the fan would continue running until the temp controller shut it down. Relay may be your best option.
     
    Last edited: Jul 10, 2017
  2. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    I put new switch in with accessory side when I did the new 12 v harness
     
  3. stubbsrodandcustom
    Joined: Dec 28, 2010
    Posts: 1,057

    stubbsrodandcustom
    Member
    from Spring tx

    sounds like alternator wiring to me.

    Basics are this. Your maintaining an electrical field to the car ignition circuit wiring keeping it excited till it bleeds voltage off. No cooling fan would do this. You could relay your ignition switch and still not fix due to the back feed comming in.

    Few things to try. Get a test light. Turn ignition on but don't start. Test your coil or Ignition box. Should be lit up. Have someone switch it off. If it turns off immediately then alternator is issue and you must isolate the sense wire by relay from your ignition wire. Make sure you have no taps from the charge output wire feeding anything other than battery. Hope this makes sense and helps.
     
  4. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    OK will look at relay. When I have the car out tomorrow and heated up so its doing the delay shut down I will try unplugging the fan and see if it shuts down right, then I will know it is the fan causing the problem. Thanks
     
  5. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    The ignition, and only the ignition should be connected to the ignition terminal on the ignition switch. Anything else should be on the accessory circuit either directly or using the accessory terminal to control relays. If nothing is connected to the ignition terminal, nothing can back feed power except a failed ignition switch.
     
  6. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    I have a HEI distributor , no coil
     
  7. Engine man
    Joined: Jan 30, 2011
    Posts: 3,476

    Engine man
    Member
    from Wisconsin

    A one wire alternator has one wire connected directly to the positive battery terminal. There is no sense wire. You're thinking of the days before the one wire when the internally regulated alternators were used with a sensing wire that was often connected to the ignition terminal when it should be connected to the accessory terminal so it doesn't back feed.
     
  8. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    What would the basic way be to incorporate a relay into the fan controller wiring. I see there Q/A"s on there site they said one could install a relay but doesn't have any information.
     
  9. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    Think I found a wiring diagram for the flex-a-lite controller and relay hook up
     
  10. raidmagic
    Joined: Dec 10, 2007
    Posts: 1,431

    raidmagic
    Member

    Of course you have a coil. It's the the cap. The large cap on top.
     
    waynos likes this.
  11. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    I was meaning no external coil
     
  12. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    This is the diagram of the [​IMG]Flex-a-lite/Relay hook up
     
    Montana1 likes this.
  13. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,145

    sunbeam
    Member

    Wire the fan to the accessory side of the switch that way the fan can't back feed the ignition.
     
  14. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    Wouldn't it be better to use a relay and not have all them amps under dash coming from the switch?
     
    Engine man likes this.
  15. crazy wheel
    Joined: Jul 31, 2011
    Posts: 64

    crazy wheel
    Member
    from Missouri

    I just went through this with my pickup after installing an electric fan.
    Yesterday I picked up a kit from the auto parts store. (Hayden 3651).
    It came with a relay, short wiring harness with fuse holders and fuses installed and an adjustable water temp sensor. It cured the issue
     
    Montana1 likes this.
  16. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,145

    sunbeam
    Member

    A lot of cars from the factory just had the temp switch hot all the time but the fan would run on after the engine was shut off until cool down.
     
  17. Yes, but you need to find the right amp blocking diode. I think it would be easier to put a relay in series.

    Kind of pricey ($79 for the kit) but I've used these on customers cars, since I don't really like the temp probe setups. Look at the sender and the 40amp relay.

    http://hotronicsproducts.com/index.php?cPath=7&osCsid=09ccf8c0f772bf1f50282783e9051daf
     
    Last edited: Jul 9, 2017
    Montana1 likes this.
  18. tom in nh
    Joined: Oct 16, 2011
    Posts: 61

    tom in nh
    Member

    Sweet Jeezus!
    This Painless wiring sounds PainFull !!!
     
    Stonebird and Montana1 like this.
  19. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    Thanks to all the positive feed back I know it's hard to diagnose a problem with out hands on. I'm going to get the car warmed up and get it doing the delayed shut down. When it does , I will try disconnecting the fan to isolate the problem if that's it I will try the relay on the fan.
     
    Montana1 likes this.
  20. ssrodder
    Joined: Jan 7, 2006
    Posts: 52

    ssrodder
    Member
    from NE PA

    If your engine stops running when you turn off the ignition when the car is still in gear means that your throttle blade is still open a slight amount. During the 70's this was common on stock vehicles. Gm installed a small cylinder type throttle stop that attached to the carburetor with an electric wire that ran to the ignition. When you turned off your car it allowed the throttle blade in the carburetor to completely close. I ran one on a 70's pickup for years. Worked great.
     
  21. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    Questions? Would this happen when engine is both cold or hot? and would any auto parts store have them or certain place?
    Thanks I will look into kit if I find out its the fan/power feeding back
     
    Corvette Fever likes this.
  22. 24riverview
    Joined: Jan 13, 2008
    Posts: 793

    24riverview
    Member

    Wiring the relay like this should be the simplest with your current setup. You should be able to find a 40 amp relay for around $10 or less.
    fan relay.jpg
     
  23. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    I might not be reading you diagram right but shouldn't one wire be coming from the battery like the diagram I posted above?
     
  24. 24riverview
    Joined: Jan 13, 2008
    Posts: 793

    24riverview
    Member

    Doesn't need to be, if it's working good now (other than the run on issue) and your 10 gauge feed wire is hooked to an adequate supply point. This way you can just add the relay near your controller without adding a bunch more wiring. 18 gauge is big enough for the jumper from #30 to #86 and the ground from #85. Keep the 10 gauge to supply #30 and #87 to controller.
     
  25. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    So I can use the 10 gauge coming from the fuse panel now, and use as the feeder for the ignition feed in your diagram splitting it to 30 and 86
     
    Last edited: Jul 10, 2017
  26. 24riverview
    Joined: Jan 13, 2008
    Posts: 793

    24riverview
    Member

    Yes, in theory key on your 10 gauge will supply power and turn on the relay. Key off, no power to relay breaking connection between the fans back feed and the rest of ignition system. Have you unhooked the fan to see if that's the issue yet?
     
  27. Blues4U
    Joined: Oct 1, 2015
    Posts: 3,654

    Blues4U
    Member
    from So Cal

    I don't like that diagram at all. The beauty of a relay is in not having to run such heavy current over long wire distance, or from the dash. It does not take much current at all to latch the relay, keep the wire to terminal 30 short it could come straight from the battery or from the battery post on the starter solenoid (though you may want to fuse it); and run a light wire from the keyed side of the fuse panel to terminal 86.
     
    Alonzo "Lon" Wilson likes this.
  28. As shown, that relay would turn on, then never go off. 86 is the relay coil, having it connected to the 30 terminal defeats the whole purpose of placing a relay in the line.

    Sent from my SAMSUNG-SM-G930A using The H.A.M.B. mobile app
     
  29. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    OK thanks. haven't tried unhooking yet to many irons in the fire, hopefully today or tomorrow.
     
  30. PeggySue
    Joined: Sep 5, 2016
    Posts: 241

    PeggySue
    Member

    Was away from home for couple weeks, Got time to do some testing on problem today, its the electric fan switch controller, as soon as the electric fan activates delay on engine shut down , unplug fan power, problem gone. Going to install relay to correct the problem, Thanks to all for the help!
     
    pat59 and Montana1 like this.

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