Wiring question for the 3rd gen gurus.

[Seanz0rz]

so, working on a couple of projects for the truck in the next couple of weeks. im trying to find a wire that is ONLY hot when the engine is running. it just needs to have enough power to kick on a relay.

off the bat i cant think of any that are hot when running that arent when the key is in the "on" position. any suggestions?

[corax]

one suggestion would be an MSD RPM switch with a rediculously low (500rpm) RPM turn on - but that way's not cheap

how about the fuel pump + wire -- it should only be on when the engine is running (maybe a few seconds when you first switch on the key to prime the fuel rail). easiest place to snag onto it would be right at or nearby the relay itself (engine compartment?)

[4runnerchevy]

I am not sure which one it is. But if you want only while running then there is a tap on the computer, as well as the fuel relay. I am sure your not looking for Acc, or Ign on. There is plenty on the circuit to fire a relay

[Seanz0rz]

this absolutely has to ONLY be on when the engine is running, never on acc or on. i might have found a compromise for me, ill have to look into it. this is my ideal solution.

[YotaFun]

here is a suggestion, how about one of the wires on the gauge cluster?
I don't know exactly what you are doing, but for instance, my driving lights I wanted to only come on when the high beams are on so what I did was taped the wire on the gauge cluster harness that lights up the high beam light on the cluster so the min that light comes on my driving lights come on.

my .02

[4runnerchevy]

Most stock fuel pumps have this for safety reasons. Only ON while running.

[4x4mike]

I think you'll be hard pressed to find something like you're looking for. What about using a switch from your ignition to power a relay. It'll only get power when it's been clicked on.

[YotaFun]

how about also sharing with us what exactly your doing :D

[Seanz0rz]

Doing this for a few reasons. Mostly to controll lighting, such as when my daytime running lights come on, when I can use my daylighters, etc

[YotaFun]

I will start looking at the wiring diagram for the 98 model and check out what you can use, I am getting good at it now lol!

[corax]

Doing this for a few reasons. Mostly to controll lighting, such as when my daytime running lights come on, when I can use my daylighters, etc


It's obviously not a 3rd gen, but what I did was grab 2 isolation posts from under the hoods of a Ford or Chevy at the junkyard - 1 for constant battery voltage, 1 for switched ignition voltage (fed by a relay) - best of all, everything fits behind the driver side kickpanel and any new wiring just requires a ring terminal and fuse holder
http://i280.photobucket.com/albums/kk171/batardsalamano/100_2718.jpg

[4runnerchevy]

post FSM diagram of the puter and electronic fuel system, and I will find your hot only while running.

[Seanz0rz]

i only have a wiring diagram for a 2002, which appears to be very different than my 98.

i think i might have found an alternative, going to experiment with it in my downtime next week.

[MTL_4runner]

Probe the wires coming off the connector on the back of the alternator for one that has power only with the engine running. I believe one of them is only hot when the alternator is charging and should give you what you're looking for.

[arjan]

I was thinking along the lines of Jamie also. Pick up voltage before the rectifier and it should work.

Another option might be the low oil pressure light. It comes on when the ignition is on, but the engine not running.
2 relays, 1 on by the ignition, the other not on (normally closed contact) parallel to the oil light and you should have it also.

[Seanz0rz]

thanks guys! thats really what i was looking for, i dont want to be drawing current away from some computer wire that i dont know what it does.

i, in looking for a different solution, thought of using a microswitch on the shifter to tell the (daytime running) lights to come on only when in drive, but that didnt solve my other need to have lights come on with the engine only.

[Seanz0rz]

so ive decided that for my daytime running lights ill put them on a microswitch that comes on when the shifter is in the drive position. should be wiring this up this weekend, ill post up what i come up with when i do it! thanks for the help!

[MTL_4runner]

so ive decided that for my daytime running lights ill put them on a microswitch that comes on when the shifter is in the drive position. should be wiring this up this weekend, ill post up what i come up with when i do it! thanks for the help!


Why not use the neutral safety switch to trigger a relay for the lights instead?

[corax]

so ive decided that for my daytime running lights ill put them on a microswitch that comes on when the shifter is in the drive position. should be wiring this up this weekend, ill post up what i come up with when i do it! thanks for the help!


Why not use the neutral safety switch to trigger a relay for the lights instead?


. . . or there may be a switch already on the shifter that you may be able to tap into instead of running your own micro switch - maybe tap off the "D" indicator circuit where it goes into the instrument cluster

also thought of another way you could trigger a relay that would only come on with the engine running -> most engine blocks have an extra oil galley plug somewhere, it'll look like a short bolt just going into the side of the block with a 10mm head (probably near the oil filter) - remove this and install an oil pressure switch (one wire type), give your relay coil power and when the engine has oil pressure the switch will provide a ground for the relay coil - those oil pressure switches are very common and all use the same pipe thread (size and pitch) - I've always used them to install oil pressure "idiot lights" as a back-up for my gauge

use this type, not the larger ones (which are variable resistance for use with a gauge)
http://www.made-in-china.com/image/2f1j00YvuEfBcPvUoMM/Oil-Pressure-Switch-TOYOTA-83530-10020-.jpg

[MTL_4runner]

also thought of another way you could trigger a relay that would only come on with the engine running -> most engine blocks have an extra oil galley plug somewhere, it'll look like a short bolt just going into the side of the block with a 10mm head (probably near the oil filter) - remove this and install an oil pressure switch (one wire type), give your relay coil power and when the engine has oil pressure the switch will provide a ground for the relay coil - those oil pressure switches are very common and all use the same pipe thread (size and pitch) - I've always used them to install oil pressure "idiot lights" as a back-up for my gauge


That's actually a pretty good way to do it provided it is an on/off type oil pressure sender and you can find a place to tap in.

[corax]

one last thought for you Sean . . . does your rear window defroster only work when the engine is running? Many modern vehicles are smart enough to only enable the rear defrost when the engine is running so the battery doesn't drain, but I'm not sure how they control it on your rig . . . does the defrost switch provide + and the Body Control Module (or some-such) provide a ground for the defrost relay when appropriate? The relay itself should only be turned on when the defrost is on (heater grid flowing current, obviously) but they may "enable" the relay on the control module side whenever the engine is running regardless of what you do to the switch -- get the drift? If it doesn't make sense, I could try explaining it better tomorrow. It's been a long day . . .

[Seanz0rz]

hrm, thanks for that keith! ill have to look into that when i get around to wiring it up. hopefully soon!