Page 1 of 2 12 LastLast
Results 1 to 15 of 16

Thread: for the electrical gurus: bridging wires from the ECU

  1. #1
    I definitely ain't a Chief Engine Builder wagonist's Avatar
    Join Date
    Jul 2005
    Location
    NSW
    Posts
    3,275

    Default for the electrical gurus: bridging wires from the ECU

    here's the scenario:
    • the car has 2 radiator fans: one for normal conditions and the other for the air con.
    • the air con has been removed.
    • each fan has a separate fused power supply direct from the battery and separate relays. ie battery - fuse - relay - fan - earth x2
    • each relay's trigger circuit gets it's +ve side from the EFI relay output ie goes to +12V when the EFI relay is triggered
    • the other side of each triggered circuit goes directly to different pins on the ECU (& I'm assuming gets pulled to ground when the fan is to be turned on)


    So basically there are 2 parallel circuits which individually trigger the fans from the ECU.
    The car is driven either fully flat stick or not at all, and as the aircon system has been removed, I'd like the fans to be both triggered simultaneously (as this is likely to be idling in the pits, or between racing stages).

    What I'd like to know is can I simply cut the aircon fan trigger wire and solder it onto the other trigger wire.
    ie can this overload the earthing of that circuit inside the ECU?

    These trigger wires are small gauge.

  2. #2
    Fear the Rapeodile Carport Converter blakeg's Avatar
    Join Date
    May 2006
    Location
    NSW
    Posts
    1,471

    Default Re: for the electrical gurus: bridging wires from the ECU

    i would personally just add a new circuit for both fans and have the original trigger wires running operating the new relay coil for simplicity.

  3. #3
    Junior Member Too Much Toyota
    Join Date
    Sep 2005
    Location
    Qld
    Posts
    5,590

    Default Re: for the electrical gurus: bridging wires from the ECU

    Quote Originally Posted by wagonist View Post
    cut the aircon fan trigger wire and solder it onto the other trigger wire.
    Do this if you are happy to have the ECU control the fan(s) - each relay pulls a few hundred mA at best so driving several thru a single pin won't hurt.

    Don't forget that with two fans powered up at the same time the batter/alt will have 20-40A load suddenly placed on it.

    You could bring the cut a/c fan trigger wire into the cabin and have it switched before heading back to the engine fan pin - allowing you to only have it power up both fans when you're not racing.

    Or use a 3-pole switch where you can earth the A/c/ trigger (in the 3rd switch position) in the cabin allowing you to turn the a/c fan without the ECU being powered up.

    And you should have a light on the switch indicating fan activity or switch position.
    ------------------------------
    ST185 road barge / MZ11 forest barge / RA65 garage barge

  4. #4
    I definitely ain't a Chief Engine Builder wagonist's Avatar
    Join Date
    Jul 2005
    Location
    NSW
    Posts
    3,275

    Default Re: for the electrical gurus: bridging wires from the ECU

    Thanks Chuckster.
    Personally, I'd rather the ECU take care of it, because then I'm sure not to forget
    And between rally stages, other things can tend to take your mind off.

    If I could've figured out which wire was required to give the ECU an aircon "on" signal, I would've done something like that instead.
    But the ECU even triggers the compressor to turn on & off.

    I may have to put some switches in the circuit at some point to turn the fans off for water crossings, but there's enough airflow that the fans don't run when on the move anyways.

    Not too fussed about the load on the alternator, apart from the engine, there's nothing else in the car to draw a load.

    oh wait, the dashboard clock...
    oh, and the tacho

    much easier do reduce weight when the car has manual everything to start with

  5. #5
    Junior Member Too Much Toyota
    Join Date
    Sep 2005
    Location
    Qld
    Posts
    5,590

    Default Re: for the electrical gurus: bridging wires from the ECU

    you'll be doing some night-time stages? if so, then allow for the light-pod and normal car lights for alternator load

    To fool the ecu about the presence (or lack thereof) of an a/c compressor, you'd have to find and fudge the sensor input from the internal thermo sensor, the over/under pressure switch and possibly a motion/pressure switch on the compressor - much easier to just bridge the two pins.

    and yes, any added lightness is a good thing. Have you taken to interior panel work with a holesaw yet
    ------------------------------
    ST185 road barge / MZ11 forest barge / RA65 garage barge

  6. #6
    Junior Member Conversion King timbosaurus's Avatar
    Join Date
    Feb 2006
    Location
    Melbourne
    Posts
    2,037

    Default Re: for the electrical gurus: bridging wires from the ECU

    Regardless of when/how you switch the fans, it'll be a decent load on an alternator.

    But your original alternator should be fine... as it's supposed to handle both fans plus a/c blower fan plus more. The only issue is you might see a momentary dip in voltage (lights flicker) and engine rev drop momentarily when they kick in.
    The simplest is ditch the ecu a/c fan output, and wire the cooling fan output to both relays. As chuckster said, a coupla hundred mA each at most... and most ecu outputs could sink twice that.
    Current rides...
    2) White RA25ST
    1) Red RA28LT (NOW WITH 1G )

  7. #7
    Its hard being a Backyard Mechanic RT40Corona4AGTE's Avatar
    Join Date
    Dec 2007
    Location
    QLD
    Posts
    458

    Default Re: for the electrical gurus: bridging wires from the ECU

    +1 for wiring both relays to the one ecu output, as others have said, we are talking mA's here and having two relays switched by one cpu pin is no big deal. It will be fine!
    1967 RT40 Corona Current Project - http://www.toymods.net/forums/showthread.php?t=46182

  8. #8
    Toymods Net Nazi Too Much Toyota river's Avatar
    Join Date
    Sep 2005
    Location
    NSW
    Posts
    7,061

    Default Re: for the electrical gurus: bridging wires from the ECU

    Hi,

    Why don't you ditch the air-con relay and just connect the air con fan off the power inputs to the existing fan. That way when the main fan kicks in, via the ECU, the air con fan is switched on also. I'm sure the relay can handle the load. Basically your main fan relay will control both fans.

    seeyuzz
    river
    The thinking man's clown and the drinking woman's sex symbol
    RA25GT - There is no substitute | 18R-G - Toyota's Dependable Masterpiece
    Toymods Car Club Treasurer, assistant Historic Plate Registrar & Forums Admin

  9. #9
    I definitely ain't a Chief Engine Builder wagonist's Avatar
    Join Date
    Jul 2005
    Location
    NSW
    Posts
    3,275

    Default Re: for the electrical gurus: bridging wires from the ECU

    Thanks for the assist, everybody. I've gone ahead and soldered the wire (& heatshrunk the joint) in the bottom of the engine bay fusebox.

    River, it is much easier this way because it was a case of only soldering one small wire onto another small wire, vs soldering a lot bigger wire.
    And considering the car may get rally use, being able to use the existing second circuit leaves a safety redundancy in the system. If one fuse or relay blows, I should still have half cooling use if needed.

    Now to find where the wire for the brake fluid/handbrake has broken away and shorted out (it's supposed to earth out when in use), so that the light on the dash goes out, instead of being half bright like it is now. It only runs from the cluster, down under the dash, then across the back of the firewall, splits to run down the left sill & under the passenger seat to the handbrake, also under the left side guard, into the engine bay behind the left headlight, then back along the sill to the brake fluid reservoir.
    And yes I've checked the switches both work.

    Following that trick, I need to find the high beam wire so I can get a trigger for the spotlights.

  10. #10
    Junior Member Backyard Mechanic
    Join Date
    Jan 2008
    Location
    queensland
    Posts
    242

    Default Re: for the electrical gurus: bridging wires from the ECU

    from the high beam headlight bulb use some light gauge twin core wire (even speaker wire if your tight) to a relay then to a switch in the cabin then back to the other side of the high beam bulb - then wire the other side of the relay as per normal for spotlights -battery to relay to lights to earth
    neil
    2009 aurion
    Purple 2000 Hilux - 1UZ

    assembly is just the opposite of disassembly - just you swear in different spots!

  11. #11
    I definitely ain't a Chief Engine Builder wagonist's Avatar
    Join Date
    Jul 2005
    Location
    NSW
    Posts
    3,275

    Default Re: for the electrical gurus: bridging wires from the ECU

    Why would I run a wire all the way from the headlight? And why do you think a relay is needed for the wire with the switch?

    But yes, you're right in getting a circuit that's universal independant on how the lights are switched.

  12. #12
    Toymods Net Nazi Too Much Toyota river's Avatar
    Join Date
    Sep 2005
    Location
    NSW
    Posts
    7,061

    Default Re: for the electrical gurus: bridging wires from the ECU

    Hi,

    When the hi beam is on your hi beam lights will get power. By connecting a relay to this power it will activate and switch on your spot lights. You need the spotties wired up to the battery and not to use the existing wiring harness or you can melt the wires. The idea of having a switch in series with the relay is so you can switch the spotties off (or on) manually, when the hi beams are active - unless you want the spotties to come on all the time when hi beam is selected..

    seeyuzz
    river
    The thinking man's clown and the drinking woman's sex symbol
    RA25GT - There is no substitute | 18R-G - Toyota's Dependable Masterpiece
    Toymods Car Club Treasurer, assistant Historic Plate Registrar & Forums Admin

  13. #13
    I definitely ain't a Chief Engine Builder wagonist's Avatar
    Join Date
    Jul 2005
    Location
    NSW
    Posts
    3,275

    Default Re: for the electrical gurus: bridging wires from the ECU

    Just re-read the post. I mistook it to be 2 relays for some reason. ie a relay for the switch & then another for the lights. Seemed like overkill.

    Problem is nowadays that the headlight switch and highbeam switch inside the car can be either power switched, or earth switched, or switch via a relay system so the go off with the ignition or some other input.
    Making sure the spotlights only work with the highbeam being on can be a bit tricky.
    Done it to pretty every car I've owned because I do a lot of rural driving.

  14. #14
    Junior Member Too Much Toyota
    Join Date
    Sep 2005
    Location
    Qld
    Posts
    5,590

    Default Re: for the electrical gurus: bridging wires from the ECU

    avoid tapping into the high-current side of the hi-beam relay. If the fuse in the supply to the factory highbeam goes, then you have no trigger for your spotlights.

    Find the trigger wire going to the high-beam relay and tap into that, run that wire to your cabin switch (for the spotlights), then from there to another relay (with it's own fused high-current supply) that powers the spots.
    ------------------------------
    ST185 road barge / MZ11 forest barge / RA65 garage barge

  15. #15
    Junior Member Backyard Mechanic
    Join Date
    Jan 2008
    Location
    queensland
    Posts
    242

    Default Re: for the electrical gurus: bridging wires from the ECU

    Quote Originally Posted by wagonist View Post
    Problem is nowadays that the headlight switch and highbeam switch inside the car can be either power switched, or earth switched, or switch via a relay system so the go off with the ignition or some other input.
    this is the reason forrunning wire to the headlights to switch the relay
    neil
    2009 aurion
    Purple 2000 Hilux - 1UZ

    assembly is just the opposite of disassembly - just you swear in different spots!

Similar Threads

  1. Replies: 16
    Last Post: 10-11-2007, 05:36 AM
  2. Electrical gurus: How can my charging system be doing this?
    By 1JZ-Rolla in forum Tech and Conversions
    Replies: 62
    Last Post: 02-09-2007, 01:33 PM
  3. Need help with bridging the neutral start switch
    By frk5how in forum Tech and Conversions
    Replies: 8
    Last Post: 28-11-2006, 11:45 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •