#8 Fuse Sparks

Discussion in 'Fox 5.0 Mustang Tech' started by chitownstang1, Jul 30, 2011.

  1. #8 Fuse, Sparks (Gremlin)

    I've been having a problem/gremlin/short i've been trying to track down and while pulling fuses went to replace the #8 Fuse and it arced. Well, I wouldn't have known it would arc if I wasn't able to hear it first with background music playing; not the cars stereo. And for those trying to help, I was not replacing a bad fuse just pullin'm. Now this fuse runs the "radio, courtesy lights, etc" and I did have the hood open so maybe there was power at the time? Closed the hood and while trying it again and still arcing out of the corner of my eye I see the stereo trying to turn on???
    My interior lights don't seem to want to turn off either that again run through this same fuse.
    Is there a door button or trunk switch that is known for going bad?

    EDIT: The more this goes on the direction continues to change OR i'm just finding more and more things that are bad, would be my luck, but plz read on to see additional findings. ANY input or similar experiences are greatly appreciated.

  2. Any circuit that has a load on it, will arc when you pull or install a fuse.

    What exactly is your original problem?
  3. I just had a problem with Fuse #9 which was welded into the fuse block and the inside was all dark brown where the surrounding plastic had melted in the fuse block ... which is the heater motor fan fuse. Put another fuse in and also put a tap on it for electric fan ... then fuse melted like taffy. Decided to solder into the back side wires and stop using that fuse holder and install a new inline fuse holder with wire. I thought it would be an easy installation just cut and solder 2 new wires. But, what I found was that Fuse #9 shares the same ground with Fuse #5 or #10 ... it could be the same power wire but I doubt it. But, they are at least sharing the same ground terminal. From what I was able to ascertain, the fan motor draws high amperage and these terminals are really too close in the fuse block. Then, add in the fact that it shares the same ground with Fuse #5 or #10 which handles another circuit then one can see that possibly the ground circuit was getting overloaded. Thus, now that the blower fan has a new fuse holder, it appears to have helped.

    So, what I am saying, if you have Fuse 8 or another fuse tapped nearby in addition to their own circuits, realize that all of it could be sharing the same ground circuit which could be being overloaded by either Fuse 8 or another surrounding fuse that shares the same ground as Fuse #8. I only know this because the back of the fuse block shows the crossover of the circuits where they share the same metal tab on the back. I am also assuming that this applies to other circuits because I believe I saw other crossovers on the back of separate fuses. This may be helpful to others also if they have circuit problems.
  4. Stock 91 Mustang

    This is in a nutshell and may not relate to one another..........

    Had a friend install a stereo. Includes 2 amps in the hatch.

    Not much later the alternator catches fire. Learned 19 years too late that there was a recall on the harness and apparently the extra juice from the stereo was the last straw.

    3g alt installed incorrectly but correct now.

    Had a fairly new MSD TFI module go bad.

    Courtesy lights stay on.* see below

    Car runs well after the eec's been reset til it slips back into almost a limp mode, it feels like anyway.

    Seems to be related to the wiring that is inline with whatever lights up the "check oil" light?

    I'll try to check in and re-explain this later. My mind is fried right now just thinking about it.

    What's the little black plastic box screwed to the chassis near the left tail/brake light? Not sure if hatch vs. trunk will matter the way it's tucked back but my car's a hatch.

    *In the mean time the "Courtesy lights" meaning the dome and trunk that wouldn't turn off as previously mentioned now work again??? I pushed both door buttons in pretty hard and jiggled and the passengers seems off or overly restrictive and the trunk the button housing is popped in place tight but the plunger itself seems to wiggle more than it should; to me anyway but it could be fine.

    And my door chime is as close to non existent as it can be but still technically does chime. (Same fuse #8)

    Thanks again for any help.
  5. So the interior lights are good now? That's usually the plungers at one of the doors or hatch.

    Msd tfi's are garbage, so just assume that issue was it's own case. FORD replacements only, anything else will fail again.

    The oil indicator light is set off by the low oil sensor in the pan, if i remember correctly it's connected to nothing important other than the light.

    When the car is in what you call limp mode, run the codes, it's probably a sensor that has gone bad.
  6. Hang on, your information bucket is about to overflow...

    What's the little black plastic box screwed to the chassis near the left tail/brake light? Not sure if hatch vs. trunk will matter the way it's tucked back but my car's a hatch.
    It is the inertia switch that shuts off the fuel pump in case of an accident.

    Car runs well after the eec's been reset til it slips back into almost a limp mode, it feels like anyway.

    Dumping the computer diagnostic codes on 86-95 Mustangs

    Revised 26-July-2011. Added need to make sure the clutch is pressed when dumping codes.

    Here's the way to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.

    Post the codes you get and I will post 86-93 model 5.0 Mustang specific code definitions and fixes. I do not have a complete listing for 94-95 model 5.0 Mustangs at this time.

    Be sure to turn off the A/C, and put the transmission in neutral when dumping the codes. On a manual transmission car, be sure to press the clutch to the floor.
    Fail to do this and you will generate a code 67 and not be able to dump the Engine Running codes.



    If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.


    The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

    89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.


    The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.

    WARNING!!! There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.

    What to expect:
    You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems. This is crucial: the same wire that provides the ground to dump the codes provides signal ground for the TPS, EGR, ACT and Map/Baro sensors. If it fails, you will have poor performance, economy and driveablity problems

    Some codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.

    Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.

    Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.

    Alternate methods:
    For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.

    Or for a nicer scanner see Equus - Digital Ford Code Reader (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
    Or for a nicer scanner see http://www.midwayautosupply.com/p-7208-equus-digital-ford-code-reader-3145.aspx– It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.

    3g alt installed incorrectly but correct now.
    Stangnet 3G install sticky http://www.stangnet.com/mustang-forums/646825-3g-alternator-install-how.html#post6673702

    Facts not present in 3G installation documents
    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 as much current, so it needs to be 4 gauge too.

    The picture shows the common ground point for the battery , computer, & 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 its 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 http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .

    Wiring diagrams and troubleshooting aids
    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

    Ignition switch wiring

    Fuel, alternator, A/C and ignition wiring

    Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs

    Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs

    Vacuum diagram 89-93 Mustangs

    HVAC vacuum diagram

    TFI module differences & pinout

    Fuse box layout

    Attached Files:

  7. I fully agree on MSD TFI modules being crap, I had mine on a MSD Pro Billet Distributor last less that a month, not even 200 Miles! Replaced it with a Motorcraft and all is well!
  8. On a side note til I can get to running codes how about "Accel" TFI Modules? I'm not trying to save a buck, but when the MSD went out I replaced it with an Accel out of convenience; long story but I inherited 2.
    I'm starting to think I should order a true Ford TFI. It's not going to solve the problem but i'll feel better I think.

    2000xp8, The oil indicator light is set off by the low oil sensor in the pan, if i remember correctly it's connected to nothing important other than the light. Can the wiring by the sensor and or the sensor itself cause a short?
    I'll check the doors and hatch. May need to be cleaned or replaced all together.

    Thanks again for the info Joe. I had a code reader from Sears and one of the 3 pins pushed back inside the reader. Til I have a chance to fix or replace it i'll try the test light method. I do have a book that gives you the source of the code. Or at least a place to begin. I'll have the codes up soon.
  9. I guess any wire could cause a short, if you think that's possible, just disconnect it.

    The accel tfi is crap too, literally they all are.
    Ford builds their parts to higher standards and because of the location of the tfi on foxes they get hot and deteriorate quickly.
  10. EDIT: I re-ran the codes below after discovering the manual trans was in gear and now DO NOT get the error code 67*.

    *67- "Neutral drive switch circuit failure, circuit open, or A/C input high." "Clutch Switch Circuit Failure." (Just had a new clutch put in???)

    85- "Canister Purge Solenoid circuit failure." "Adaptive fuel limit reached-lean." "Shift Solenoid 3/4-4/3."


    33- "EGR Valve not opening."

    Not sure if 85 and 33 are related but the smog equipment has been removed.

    The A/C was also removed and am not sure how the wiring was taking care of. I already know when the upgrade to a 3g alt. went down the wires were done wrong and since corrected which leads me to wonder what may have possibly gone wrong with this? For example, I found the original power wire to the old alternator cut and tucked under the air box, exposed! You could see tiny copper wire threads sticking out the top which theoretically were touching the body/frame of the car; by the time I discovered it I had already moved it so i'm not positive the wire was in contact but when I laid it back down to simulate where it might have been it very well could've been in contact. Could the A/C have been disconnected the same manner leaving me with a short?

    Here's a side question. I tested the voltage from the connector that leads to the engine bay light, near the test connector location for the eec and got 12 volts. I closed the hood and got the same reading. Kinda reminds me as a kid if the refrigerator light turns off or not, lol? But I just can't see that bulb being lite all the time you're driving regardless of need.

    Thx again!
  11. There is no vaild code 10. That's the scanner displaying a single flash before dumping the codes.

    Code 33 - Insufficient EGR flow detected.
    Look for vacuum leaks, cracked vacuum lines, failed EGR vacuum regulator. Check to see if you have 10” of vacuum at the EGR vacuum connection coming from the intake manifold. Look for electrical signal at the vacuum regulator solenoid valves located on the rear of the passenger side wheel well. Using a test light across the electrical connector, it should flicker as the electrical signal flickers. Remember that the computer does not source any power, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.
    Check for resistance between the brown/lt green wire on the EGR sensor and pin 27 on the computer: you should have less than 1.5 ohm.

    See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host)



    EGR test procedure courtesy of cjones

    to check the EGR valve:
    bring the engine to normal temp.

    connect a vacuum pump to the EGR Valve or see the EGR test jig drawing below. Connnect the test jig or to directly to manifold vacuum.

    Do not connect the EGR test jig to the EVR (Electronic Vacuum Regulator).

    apply 5in vacuum to the valve. Using the test jig, use your finger to vary the vacuum

    if engine stumbled or died then EGR Valve and passage(there is a passageway through the heads and intake) are good.

    if engine did NOT stumble or die then either the EGR Valve is bad and/or the passage is blocked.

    if engine stumbled, connect EGR test jig to the hose coming off of the EGR Valve.
    Use your finger to cap the open port on the vacuum tee.
    snap throttle to 2500 RPM (remember snap the throttle don't hold it there).
    did the vacuum gauge show about 2-5 in vacuum?
    if not the EVR has failed

    EGR test jig

    The operation of the EGR vacuum regulator can be checked by using a test light applied across the wiring connector. Jumper the computer into self test mode and turn the key on but do not start the engine. You will hear all the actuators (including the EVR vacuum regulator) cycle. Watch for the light to flicker: that means the computer has signaled the EGR vacuum regulator successfully.

    Code 67 - clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position when codes where dumped. Possible neutral safety switch or wiring problem. This code may prevent you from running the Key On Engine On tests. You can generally ignore this code, since it has no effect on engine performance.

    The computer wants to make sure the A/C is off due to the added load on the engine for the engine running tests. It also checks to see that the transmission is in Neutral and the clutch depressed (T5, T56, Tremec 3550 & TKO)). This prevents the diagnostics from being run when the car is driven. Key On Engine Running test mode takes the throttle control away from the driver for several tests. This could prove hazardous if the computer was jumpered into test mode and then driven.

    The NSS code 67 can be bypassed for testing. You will need to temporarily ground computer pin 30 to the chassis. Computer pin 30 uses a Lt blue/yellow wire. Remove the passenger side kick panel and then remove the plastic cover from the computer wiring connector. Use a safety pin to probe the connector from the rear. Jumper the safety pin to the ground near the computer.
    Be sure to remove the jumper BEFORE attempting to drive the car!!!

    Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check vacuum lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation. Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
    The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any time the ignition switch is in the run position.

    Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose. Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel. The canister is normally mounted on the passenger side frame rail near the smog pump pulley.


    It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook it up & use it?

    The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the carbon canister.

    Purge valve solenoid:

    The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
    Carbon Canister:
  12. Long story short, i'm back and can properly dedicate time to this.

    All the EGR/smog gear has been removed. It was not done for performance purposes but much was damaged after a fire I had in 2009. I can't recall the name of it but there's an item you plug into your that tells your computer all is well with the EGR and also turns off the check engine light.

    I'll check for leaks but I just blew smoke through it a few weeks ago and all looked good.

    I'll check the EGR wiring per your post and see what we get. Curious about the A/C power feed too. Where it comes from and if it was removed correctly. The same guy that incorrectly tucked away the org. main power wire during an alternator upgrade is the same guy that removed the a/c and smog gear. I've learned he talks better than he delivers. But that's why i'm here, talk to the ones that walk the walk vs. talk the talk.
    Thanks again! I'll post updates soon.
  13. Dont suppose you'll be visiting the Chicago area anytime soon? lol. I'm good for at least the air fair!