86 Starter solenoid wire hook ups

Discussion in 'Fox 5.0 Mustang Tech' started by fordkid, Nov 21, 2009.

  1. Hey, I have searched since I figured this question has been asked before. the only thread I found had different wires then mine, so here I am.

    first off I am posting this question here because the engine, transmission computer and BOTH wiring harnesses are from an 86 5.0 it is in a 66 mustang now, trying to get power to the engine and no dice. whitch wires hook up to which side of the solenoid. check out my pics. I am using both wireing harnesses for two reasons, I am too cheap to spend the 600 bucks for the painless wire harness. and I also want to keep the cruse control. as well as upgrade the headlights on my 66 mustang. figured my problem had to be at the soleinoid since all the other wires are facotry plugs so even an idiot like me can't screw that up.

    is the little wire in my hand a ground wire?

    Ford Kid

    Attached Files:

  2. Starter solenoid wiring 86-91 5.0 Mustangs with standard starter


    Starter solenoid wiring 92-93 Model cars and earlier models with high torque mini starter.


    Grounds are important to any electrical system, and especially to
    computer controlled engines. In an automobile, the ground is
    the return path for power to get back to the alternator and battery.

    1.) The main power ground is from engine block to battery: it is
    the power ground for the starter & alternator.

    2.) The secondary power ground is between the back of the
    intake manifold and the driver's side firewall. It is often missing or
    loose. It supplies ground for the alternator, A/C compressor
    clutch and other electrical accessories such as the gauges.
    Any car that has a 3G or high output current alternator needs
    a 4 gauge ground wire running from the block to the chassis
    ground where the battery pigtail ground connects.

    The 3G has a 130 amp capacity, so you wire the power side
    with 4 gauge wire. It stands to reason that the ground side
    handles just a much current, so it needs to be 4 gauge too.

    The picture shows the common ground point for the battery & extra 3G
    alternator ground wire as described above in paragraph 2. A screwdriver
    points to the bolt that is the common ground point.
    The battery common ground is a 10 gauge pigtail with the computer ground
    attached to it.

    Picture courtesy timewarped1972

    Correct negative battery ground cable.

    3.) The computer has its own dedicated power ground that comes off the ground pigtail
    on the battery ground wire. Due to it's proximity to the battery, it may become
    corroded by acid fumes from the battery.
    In 86-90 model cars, it is a black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire.
    In 91-95 model cars it is a black cylinder about 2 1/2" long by 1" diameter with a black/white wire.
    You'll find it up next to the starter solenoid where the wire goes into the wiring harness.

    4.) All the sensors have a common separate ground. This
    includes the TPS, ACT, EGE, BAP, & VSS sensors.

    5.) The O2 sensor heaters have their own ground (HEGO ground)
    coming from the computer. This is different and separate from
    the O2 sensor ground. It is an orange wire with a ring terminal
    on it. It is located in the fuel injector wiring harness and comes out
    under the throttle body. It gets connected to a manifold or bolt on
    back of the cylinder head.

    6.) The TFI module has 2 grounds: one for the foil shield around
    the wires and another for the module itself. The TFI module
    ground terminates inside the computer.

    7.) The computer takes the shield ground for the TFI module and
    runs it from pin 20 to the chassis near the computer.

    8.) The computer's main power ground (the one that comes from
    the battery ground wire) uses pins 40 & 60 for all the things it
    controls internally.

    See Automotive Test Tools for help for help troubleshooting voltage drops across connections and components. .


    Extra grounds are like the reserve parachute for a sky diver.
    If the main one fails, there is always your reserve.

    The best plan is to have all the grounds meet at one central spot
    and connect together there. That eliminates any voltage drops
    from grounds connected at different places. A voltage drop
    between the computer ground and the alternator power ground will effectively
    reduce the voltage available to the computer by the amount of the drop.
  3. The wire in your hand should go on the right post so that it gets battery power all of the time.

    I'm not sure what power circuit it feeds.

    There's always only one wire one the left post - the one that goes to the stater. Some people that do a mini-starter upgrade will connect two wires to that post - that's VERY WRONG and is a great way to f***** up the flywheel because of the starter "hanging" after a start. See the Ford instructions on a mini-starter upgrade for more info.

    Good Luck!
  4. Holy crap I'm an idiot. Completely forgot about the ground wire comming from the engine block going to the firewall. I will also double check all the other grounds. and that's easy enough. always only one wire going to the left post.

    Thank you so much, your guys's help is greatly appreciated. will let you know when everything is done.

    Ford Kid
  5. Hey guys/gals

    Things are looking up. I am fairly sure I have a wire problem. before I spend hours looking for it thought I would check and see if anyone can narrow it down for me.

    I hooked up the ground wire I was forgetting about. and checked the rest. they look good. when I turn the key it clicks, not when I turn to the start position, it clicks when I turn the key ON, and then when I trun it to the start position nothing happens. I checked for the basic voltage drop problems, couldn't find anything. when I jump the two big terminals on across the solenoid it just sparks, the engine doesn't crank. when I jump the power side terminal to the little screw post the engine cranks, so I am thinking the solenoid is good and I have wires routed where they shouldn't be. since I did completely remove the harnesses from one car and put them in another car. I can get the lights to turn on too. I haven't deleted that part of the harness yet. probably won't since I want to put some modern brighter lights in the 66. any ideas where I should check,

    Ford Kid
  6. No Crank checklist for 5.0 Mustangs

    Revised 09-July-2009 to reorder stuck solenoid help.

    No crank and stuck starter solenoid problems have the same root causes – low battery voltage and poor connections. For that reason, they are grouped together.
    Use the same initial group of tests to find the root cause of both no crank and stuck solenoid problems.

    Since some of the tests will bypass the safety interlocks, make sure that the car is in neutral and the parking brake is set. Becoming a pancake isn’t part of the repair process…

    1.) Will the car start if it is jumped? Then clean battery terminals and check battery for low charge and dead cells. A good battery will measure 12-13 volts at full charge with the ignition switch in the Run position but without the engine running.
    A voltmeter placed across the battery terminals should show a minimum of 9.5-10 volts when the ignition switch is turned to the Start position and the starter engages or tries to engage. Less than this will result in a clicking solenoid, or slow cranking (if it cranks at all) or a starter solenoid that sticks and welds the contacts together.

    Most auto parts stores will check your battery for free. It does not have to be installed in the car to have it checked; you can carry it with you to the auto parts store.

    The battery posts and inside of the battery post terminals should be scraped clean with a knife or battery post cleaner tool. This little trick will fix a surprising number of no start problems.

    The clamp on with 2 bolts battery terminal ends are a know problem causer. Any place you see green on a copper wire is corrosion. Corrosion gets in the clamped joint and works its way up the wire under the insulation. Corroded connections do not conduct electricity well. Avoid them like the plague...

    If the starter solenoid welds the contacts, then the starter will attempt to run anytime there is power in the battery. The cables and solenoid will get very hot, and may even start smoking. The temporary fix for a welded starter solenoid is to disconnect the battery and smack the back of the solenoid housing a sharp blow with a hammer. This may cause the contacts to unstuck and work normally for a while.

    A voltmeter is handy if you are familiar with how to use it to find bad connections. Measure the voltage drop across a connection while trying to start the car: more than .5 volts across a connection indicates a problem.

    See Automotive Test Tools for help for help troubleshooting voltage drops across connections and components. .


    2.) Check the battery to engine block ground down near the oil filter, and the ground behind the engine to the firewall. All grounds should be clean and shiny. Use some sandpaper to clean them up.

    3.) Jump the big terminals on the starter solenoid next to the battery with a screwdriver - watch out for the sparks! If the engine cranks, the starter and power wiring is good. The starter relay is also known as a starter solenoid.

    The rest of the tech note only concerns no crank problems. If your problem was a stuck solenoid, go back to step 1.

    4.) Then pull the small push on connector (small red/blue wire) off the starter solenoid (Looks like it is stuck on a screw). Then jump between the screw and the terminal that is connected to the battery. If it cranks, the relay is good and your problem is in the rest of the circuit.

    5.) Remember to check the ignition switch, neutral safety switch on auto trans and the clutch safety switch on manual trans cars. If they are good, then you have wiring problems.

    Typical start circuit...
    Diagram courtesy of Tmoss & Stang&2birds

    6.) Pull the starter and take it to AutoZone or Pep Boys and have them test it. Starter fails test, then replace it. If you got this far, the starter is probably bad.

    Starter solenoid wiring for 86-91 Mustang

    Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.

    Electrical checks for the switches and starter solenoid

    Remove the small red/blue wire from the starter solenoid. Use a screwdriver to bridge the connection from the battery positive connection on the starter solenoid to the small screw where the red/blue wire was connected. The starter should crank the engine. If it does not, the starter solenoid is defective.

    If the starter does crank the engine, the problem is in the clutch safety circuit (5 speed) or Neutral Sense Switch (auto trans) or ignition switch.

    Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.

    Typical start circuit...
    Diagram courtesy of Tmoss & Stang&2birds

    You will need a voltmeter or test lamp for the rest of the checks. Connect one lead of the voltmeter or test lamp to ground. The other lead will connect to the item under test.
    Look for 12 volts on the white/pink wire when the ignition switch is turned to the Start position. Check the ignition switch first.
    No 12 volts, replace the ignition switch.

    The next step will require you to push the clutch pedal to the floor (5 speed) or put the transmission in neutral (auto trans) while the ignition switch is turned to the Start position.
    Good 12 volts, check the clutch safety switch (5 speed) or Neutral Sense Switch (auto trans) for good 12 volts on both sides of the switches. No 12 volts on both sides of the switch and the switches are defective or out of adjustment. Check the wiring for bad connections while you are at it.
  7. Hey,

    the little wire going to the little screw post on the starter relay only has 3 volts when the ignition is turned to the start position. since there is some voltage you think I should be looking for another bad ground. or is the switch bad. the switch wasn't bad when I took it out of the 86 but then again the car had been sitting for a while due to a bad fuel pump.

    Ford Kid
  8. The wire in the center of the relay "turn the relay on". So, when the "center wire" gets 12V, the relay connects the battery terminal "front" to the starter terminal "back".

    A remote starter button and a volt meter are good to have.

    You shouldn't have any voltage on the "center wire" unless the key is in the "Start" position. But, a DVM may read lower voltage that gets leaked through high resistance paths. So, if you read "3Volts" on the "center wire" with the key in the "ON" position (not start!), then I don't think that would be the problem now .

    If you can get the starter to crank with by jumping the center wire, but not with the key in the "Start" position, then you have a wire or ignition switch problem.

    Good Luck!
  9. Yea I am fairly certain it's a wire problem. I have no voltage on that wire when the key is ON, and only 3 volts when the key is turned to the START position.

    Ford Kid