So I have the much disrespected cobra 75 wiring loom. I was told to put relays with diode protection built I. When I switch them out I now blow fuse 18 factory fuse. Why? I put the tycos back in and at least I can start the car. This fuse is got tons of stuff on it. Head lamp . Cigar lighter , speed sensor. And I can't do diagnostics without that circuit. What does the diode change? Mustang 5.0 from 1990
Well atleast you got it to start up.....I think you said you never got it to run so your heading in the right direction....
Heres the direction I went after getting contacted by a professional via pm about the errors my harness still had and it really opened my eyes as to how ford got the cleanest grounds to the ECU and why pins #37 & #57 also pins #40 and #60 are important for the way the ECU gauges its power to ground resistances............
I undid the whole harness again and separated all of the systems and wrapped each in protective copper foil tape then wrapped over the copper foil tape with harness wrap...........Found out that I had to also separate pins #40 and 60 plus the EEC relay ground wires....Like this...
My harness now has 6 seperate grounding wires....one of the wires is the two 02 sensor wires melded into 1
Fuse #18?...............I dont have anywhere in my instructions that says to hook a wire to fuse #18 or any fuse in the fuse panel ............
My "KEY ON" wire I tapped direct off the ignition switch wires on the switchplug going to pins # I1 and I2 labeled Run Output for Engine.
The purple TFI start wire I tapped off the ignition switch too on wire on pin labeled ST for Start Output..........
The fuelpump wire should be hooked to the fuelpump relay trigger wire coming off the fuelpump relay plug under the passenger seat....You cut the wire off the relay and hook the pink wire to it...I do away with the inertia switch provision on the pink wire by cutting off the plug and hooking the pink and fuelpump output wires together because the stock inertia switch is wired into the FP relay youre wiring into..
Cant do diagnostics without the circuit?.. What circuit?... Are you referring to the MIL Lamp power wire being hooked to fuse #18?
FYI:..........The MIL power wire Does NOT Hook UP to ANY Outside 12v POWER source with a FUSE....The red Mil Power wire already has 12v power to give the 12v power to power the Check engine light bulb so in essence you're temporarily creating 24volts to that circuit with the diode with an immediate short to ground for the temp overvolt condition until the fuse blows...
Its just two wires that makes the check engine bulb illuminate and you have to make a bulb work and fit inside your cluster...The wires are red and tan...It doesnt matter which one is negative or positive as the T-10 style bulb doesnt care...
I took a regular bayonette style bulb holder from an old oil pressure gauge with bayonette bulb and modified it to replace the stock check engine bulb holder and mounted it in my cluster...you can simply use one of these too...
You get 2 for $10.00 on ebay...
The harness is a stand alone system and uses the diagnostic plug with seperate wire to make the check engine light blink.........
This is how you do diagnostics.............
View: https://vimeo.com/766330560