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Thread: Which Circuits Have 12v ON & START?

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    Member sluggish91's Avatar
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    Default Which Circuits Have 12v ON & START?

    The car I'm working on is my dad's 91 Marquis.
    The question I am seeking help on is as follows:
    Which circuit has 12v with the key in the ON and the START postions, but NOT have power when the ignition is OFF?
    I discovered the radio circuit fit two of these criteria (12v ON, no power OFF), but failed to check if it had 12v in the START position.
    It would be a great help if someone already knows whether or not the radio circuit fits all three of these criteria.
    If it does not, can someone help me determine which circuit does, or how I can find it?
    I am working on installing an aftermarket engine management system on this vehicle and need to find a circuit as such.
    Thank you to everyone for your all help.
    1985 2-Door
    CFI, K&N Filter, Edelbrock Performer 289 Intake, E7 Heads, BBK Shorty Headers, Summit H-pipe, Hooker Max Flow Mufflers, E-Fan, 3G Alternator, Race Crank Pulley, Bilstein Rear Shocks, KYB Front Shocks, Front Lowering Springs, FTI 2400 Stall Converter, PA Performance Valve Body, Motive 4.30 Gear, Eaton LSD Differential - I own quite possibly the fastest CFI powered box to the 1/8th mile: 9.95@68.89mph

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    all the CFI are belong to me
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    How much of the rest of the car is getting deleted? I would just use the factory ECM power relay, since that meets your needs if it will still be in the car. On a 91, that lives in the compartment attached to the black plastic vacuum reservoir on the driver side fender.

    That relay is activated when the switch is in Run or Start. The wire colours are Red/Light Green coming from the ignition switch for Run, and Brown/Pink coming from the ignition switch for Start. They combine at a splice and continue to the relay as Red/Light Green. You should not use that wire as your power supply, you should only use it to switch a relay and use the relay to power your new stuff.

    Current driver: 85 Ranger
    Panthers, Parked: 83 GM 2dr POTM 10/2019 | 84 TC POTM 1/2017 & 4/2019 | 85 CS | 86 GM | 88 TC | 91 GM POTM 12/2017
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    Which system are you going with? I toyed with the idea of a megasquirt plug and play for a fox but for me it probably wouldn’t be worth it.


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    Lost and driftin' Arquemann's Avatar
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    I don' know if SEFI is the same as CFI with the ECM and fuel pump relays.
    Atleast on EEC-IV CFI, the fuel pump relay gets the signal from the ECM, so hopefully your engine management does the same, if it uses the factory ecm connector.

    I will be doing a carb conversion, and I'll be routing the power side of the ECM relay to the fuel pump.
    ECM relay is always hot from the battery, and gets the signal from the ign switch.
    1985 Mercury Grand Marquis LS, "Maisa"
    2008 BMW 530d Touring, "Femma"

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    I'm an air-conditioned gypsy gadget73's Avatar
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    almost nothing still has power in start except the ECM feed. The ignition doesn't even have start-on power, there is a secondary feed to take over when cranking.

    If you're doing involved wiring work, you really need the EVTM.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

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    Donating Member massacre's Avatar
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    Quote Originally Posted by gadget73 View Post
    almost nothing still has power in start except the ECM feed. The ignition doesn't even have start-on power, there is a secondary feed to take over when cranking.

    If you're doing involved wiring work, you really need the EVTM.
    Agreed.

    Trying to do it without one is kind of flying blind.
    ..

  7. #7
    all the CFI are belong to me
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    FWIW, my information above is from the 91 EVTM.

    I echo the sentiment that anyone doing this type of work really needs a copy of that book.

    Current driver: 85 Ranger
    Panthers, Parked: 83 GM 2dr POTM 10/2019 | 84 TC POTM 1/2017 & 4/2019 | 85 CS | 86 GM | 88 TC | 91 GM POTM 12/2017
    Not Panthers, Parked: Ranger trailer | 05 Focus | 04 Focus
    RIP: 97 CV | 83 TC
    Junkyards

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    Member sluggish91's Avatar
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    Quote Originally Posted by kishy View Post
    How much of the rest of the car is getting deleted? I would just use the factory ECM power relay, since that meets your needs if it will still be in the car. On a 91, that lives in the compartment attached to the black plastic vacuum reservoir on the driver side fender.

    That relay is activated when the switch is in Run or Start. The wire colours are Red/Light Green coming from the ignition switch for Run, and Brown/Pink coming from the ignition switch for Start. They combine at a splice and continue to the relay as Red/Light Green. You should not use that wire as your power supply, you should only use it to switch a relay and use the relay to power your new stuff.
    I greatly appreciate this information. This was what I was looking for. I am removing the engine harness & factory ECM and installing an aftermarket EFI system.

    Quote Originally Posted by 87GrandMarq View Post
    Which system are you going with? I toyed with the idea of a megasquirt plug and play for a fox but for me it probably wouldn’t be worth it.

    Sent from my iPhone using Tapatalk
    I convinced my Dad to go with the Pro-M EFI system. It's been a 3-4 year project overall but I started the Pro-M installation this year. The system is really top notch and I recommend it to anyone, although the installation has been quite involved on this 91. It's only my second time installing an aftermarket engine management system.
    1985 2-Door
    CFI, K&N Filter, Edelbrock Performer 289 Intake, E7 Heads, BBK Shorty Headers, Summit H-pipe, Hooker Max Flow Mufflers, E-Fan, 3G Alternator, Race Crank Pulley, Bilstein Rear Shocks, KYB Front Shocks, Front Lowering Springs, FTI 2400 Stall Converter, PA Performance Valve Body, Motive 4.30 Gear, Eaton LSD Differential - I own quite possibly the fastest CFI powered box to the 1/8th mile: 9.95@68.89mph

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    Member sluggish91's Avatar
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    Would there be anywhere else aside from the factory ECM power relay I could tap into?

    We pretty much got rid of the entire factory engine harness/ECM harness and that included the factory ECM power relay kishy was talking about.

    This is the direct quote from the Pro-M manual:
    "
    Connect the Orange wire marked “KEYED RUN” to the keyed ignition switch. This
    wire must have +12 volts with the key in RUN and START positions. In other words,
    it must have 12V when the key is “on” AND when the engine is cranking. It must
    NOT have power when the ignition is “OFF”.
    "

    Thanks everyone for their help and input.
    1985 2-Door
    CFI, K&N Filter, Edelbrock Performer 289 Intake, E7 Heads, BBK Shorty Headers, Summit H-pipe, Hooker Max Flow Mufflers, E-Fan, 3G Alternator, Race Crank Pulley, Bilstein Rear Shocks, KYB Front Shocks, Front Lowering Springs, FTI 2400 Stall Converter, PA Performance Valve Body, Motive 4.30 Gear, Eaton LSD Differential - I own quite possibly the fastest CFI powered box to the 1/8th mile: 9.95@68.89mph

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    Donating Member massacre's Avatar
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    I recently went through this on my fox, i used a test light to find a wire at the ignition switch that was hot in both start and run. On my car it ended up being a white/light blue wire that went from ignition switch to the ignition control module. Confirmed by checking the EVTM.
    I am no longer using the ignition module so that works for me. Your car is probably different, my donor harness and ignition switch are probably more like yours, with the previously mentioned brown/pink and red/green wires.

    Not sure if you could splice those 2 wires together into 1 wire to get you sorted?
    ..

  11. #11
    all the CFI are belong to me
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    The wire to turn on that relay comes through the firewall. It is somewhere available to you, you just need to find it. Then use it to power a relay, not as a power source itself.

    Current driver: 85 Ranger
    Panthers, Parked: 83 GM 2dr POTM 10/2019 | 84 TC POTM 1/2017 & 4/2019 | 85 CS | 86 GM | 88 TC | 91 GM POTM 12/2017
    Not Panthers, Parked: Ranger trailer | 05 Focus | 04 Focus
    RIP: 97 CV | 83 TC
    Junkyards

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    Donating Member massacre's Avatar
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    Quote Originally Posted by kishy View Post
    The wire to turn on that relay comes through the firewall. It is somewhere available to you, you just need to find it. Then use it to power a relay, not as a power source itself.
    Agreed. That is what i am doing. I'm taking it a step further by using a relay to power a 6 circuit fuse panel for other additional switched circuits.
    Lots of fuses everywhere, don't want to burn up wires/start a fire lol
    ..

  13. #13
    I'm an air-conditioned gypsy gadget73's Avatar
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    using relays to unload the ignition switch is generally a good idea on these. Too much current runs through that thing and its a known weak point. Its the crossing point of modern cars with lots of electronics and old design that didn't believe in adding extra parts to the circuits. Its that whole "it can't fail if its not there" philosophy.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  14. #14
    Donating Member massacre's Avatar
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    Quote Originally Posted by gadget73 View Post
    using relays to unload the ignition switch is generally a good idea on these. Too much current runs through that thing and its a known weak point. Its the crossing point of modern cars with lots of electronics and old design that didn't believe in adding extra parts to the circuits. Its that whole "it can't fail if its not there" philosophy.
    Totally agree.
    My eec pulls 30 amps, and fuel pump is 20 amps. Stock Fox fuse box has cylindrical glass fuses, and the biggest one is 20 amps.
    Sending 50 amps through the stock ignition switch sounds like a fire waiting to happen.

    So going to use a relay. I was able to find a relay that has a built in 30a fuse, which is nice and saves hassle and space.

    ..

  15. #15
    Member sluggish91's Avatar
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    Thanks again everyone for the help, I am thinking of getting a 70 amp relay.
    Would that be overkill, or is this a situation where overkill is a good thing?
    I'm still a bit fresh to the electrical theory but I am learning as I go.
    I have a book about custom auto wiring and electrical I am reading, so that is helping my confidence with all this stuff.
    Massacre, that is a nifty relay there with the fuse connected right to it.
    I tried finding one like that on Summit but my search came up empty.
    1985 2-Door
    CFI, K&N Filter, Edelbrock Performer 289 Intake, E7 Heads, BBK Shorty Headers, Summit H-pipe, Hooker Max Flow Mufflers, E-Fan, 3G Alternator, Race Crank Pulley, Bilstein Rear Shocks, KYB Front Shocks, Front Lowering Springs, FTI 2400 Stall Converter, PA Performance Valve Body, Motive 4.30 Gear, Eaton LSD Differential - I own quite possibly the fastest CFI powered box to the 1/8th mile: 9.95@68.89mph

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    Donating Member massacre's Avatar
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    https://www.walmart.com/ip/Mgaxyff-C...erId=101006085

    70 sounds kinda high, maybe ask the manufacturer of your system what they like to see for fuses? Fuses protect the wiring, so for 70 amps i would think you'd need some pretty large wire.

    Click image for larger version. 

Name:	a6448405-101-wire_chart.gif 
Views:	4 
Size:	87.1 KB 
ID:	57169

    There are charts like this available on the internet, not saying this one is particularly good or accurate.
    Last edited by massacre; 10-28-2021 at 08:24 AM.
    ..

  17. #17
    I'm an air-conditioned gypsy gadget73's Avatar
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    the typical Bosch relays are 30 or 40 amp. Should be enough for most things honestly. The connectors on those things tend to be the weak point. The cheap relay + socket packages you can find everywhere have thin garbage wire in fat insulation. Gets awful warm at the crimp with heavy load and then you have problems. I have some of those but won't run them more than about half their rated load and I don't use them for anything important. The key-on cig lighter for my phone charger can fail and it doesn't matter. Not going to trust an ECM to that.
    Last edited by gadget73; 10-31-2021 at 08:36 PM.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

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    Donating Member massacre's Avatar
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    I'm using the relay but not a socket. Good looking out on the relay sockets. I looked into sockets but decided against it.
    ..

  19. #19
    I'm an air-conditioned gypsy gadget73's Avatar
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    single biggest reason I like the sockets is if I have to change the relay I don't have to pay attention to where the wires go.

    86 Lincoln Town Car (Galactica).
    5.0 HO, CompCams XE258,Scorpion 1.72 roller rockers, 3.55 K code rear, tow package, BHPerformance ported E7 heads, Tmoss Explorer intake, 65mm throttle body, Hedman 1 5/8" headers, 2.5" dual exhaust, ASP underdrive pulley

    91 Lincoln Mark VII LSC SE, triple black (Timewarp) - poly front bushings, KYB struts and shocks, Holley SystemMax1 lower intake, SilverFox AOD valve body,

    1984 Lincoln Continental TurboDiesel - rolls coal

    Quote Originally Posted by phayzer5 View Post
    I drive a Lincoln. I can't be bothered to shift like the peasants and rabble rousers

  20. #20
    Donating Member massacre's Avatar
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    Quote Originally Posted by gadget73 View Post
    single biggest reason I like the sockets is if I have to change the relay I don't have to pay attention to where the wires go.
    Good point
    ..

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