Wiring Issues 89 Gt

Electrical problems listed under the Tuning forum limits your chances for getting help. If you had put this post in 5.0 Tech, you would have had more input...

Having said that, here's what I can do to help you.
PM me your email address and I will send you a complete Ford Factory 89 Mustang electrical diagram set. The zip file is 2.5 MB and is too big to fit through Stangnet's email gateway.
89 Mustang wiring diagrams zip package–

They are in a zip file format to reduce the size of the package. If you don't have Windows 7 or Windows 8, you’ll need WinZip or other Windows archive tool to extract them from the zip file. See www.majorgeeks.com - Download Freeware and Shareware Computer Utilities for a free download.
The diagrams show the location area and the connectors are drawn to the same shape as those in the car.
You will need the Adobe Acrobat viewer which is also a free download – www.adobe.com/products/acrobat/readstep2.html - Adobe Reader download - All versions

SEE Mustang GT Fog Light Fix to fix the foglight problem. The stock wiring isn't up to the job and is overheating. The headlight switch & turn/multifunction switch are affected by Ford's wiring problem. Sometimes it overheats so badly that the plastic shells of the wiring connectors start to melt. This will show you how to add a relay to the fog lights to relieve the overload on the headlight wiring.

Be careful not to use bulbs rated at more than 55 watt each with the stock fog light wiring. Using oversize bulbs can result in overheating the wiring harness and electrical fires. Definitely do the fog light fix first.

I did mine differently, but I had to build my own wiring harness for the fog lights. This is more trouble than it is worth for most folks. I left all the wiring on the stock light switches in place and used the fog light wiring to power the relay coil. The other side of the relay coil is connected to ground. I have an inline fuse that picks up power from the battery side of the starter solenoid. It is connected to the relay contact. The other relay contact is connected to the new wiring harness I made for the fog lights.



The advantage of making your own foglight wiring harness is that you can run 100 watt fog light bulbs. The stock wiring harness will not use 100 watt bulbs without overloading and causing a fire.

Unless you are good at electrical wiring, have the skills and tools (crimp tool, soldering gun, heat gun for the heat shrink tubing, etc.) I recommend that you stick with the Corral method.

Technical explanation of why the wiring and switches overheat.
You asked for it...

I= Current
E= Voltage
R= Resistance
W= Watts

Two 55 watt fog lamps =110 watts. Find the current in the circuit
I= W/E
110 watts/14 volts = 7.85 amps for fog lights alone.
Since the lighting circuit supplies headlights, taillights, and parking lights, etc.

56 watts 2 each GE Part # L3156 corner light 28 watts each
90 watts 2 each GE Part # 9004 headlight 45/65 watts each (low beam)
63 watts 2 each GE Part # L194 parking light 31.5 watts each
56 watts 2 each GE Part # L3157 tail light 28 watts each
265 watts Total

Total other exterior lighting current
I=W/E
265 watts/14 volts = 18.92 amps
18.92 amps other exterior lighting current
+ 7.85 amps fog light current
26.77 amps with all exterior lights and fog lights on.

The 12 gauge power feed wire to the exterior lighting switch is rated at 20 amps
26.77
- 20.00
6.77 amps excess current

7.85 amps used by fog lights
-6.77 amps excess current
1.08 amps to run the fog lights left if you stay within the 20 amp limit of the wire.
With 1.08 amp of current, the fog lights probably won’t produce any useable light.

Added resistance required to reduce fog light current to permissible 20 amp limit
R=E/I
14 volts/6.77 amps = 2.06 ohms
Resistor wattage
W=EI
14 volts x 6.77 amps = 94.78 watts
You would need a 2 ohm, 100 watt resistor.

Light bulb ratings from http://www.roadparts.com/catalog/section30.pdf
Radio shack resistor catalog - no matches , and no combinations that could be used to make a 100 watt, 2 Ohm resistor.
See RadioShack.com

Ohm’s law – in case you have any questions about my formulas - Ohm's Law Calculators

Everything starts with the battery connection to the starter solenoid and branches off from there.
Starter solenoid wiring 86-91 model cars.

That's pretty awesome I was just wondering about the fusible links since I don't know much about them. I put in a new distributor and coil and then suddenly had no spark. So I put the old stuff back in (which worked perfectly the day before) and still had no spark. I had no problems before and did a simple (I thought) dist./coil swap and now the car won't start. I've done the no start checklist and about all that's left is a fusible link. Even though like I said car was fine immediately before dist./coil swap.

Don't hijack someone else's post, it's bad manners and makes for confusion on what answer is for what post.

You put your thread in a forum specifically for people who have tuning questions about things like injectors, MAFs and aftermarket tuners such as Tweecer, Moates or Anderson PMS. Therefore you post will not been seen by people who may have an answer but do not visit the Tuner forum. Convertible top problems have nothing to do with tuning an engine.

Make your post in 5.0 Tech and I will try to help you.

If previous post is directed to me I apologize. For days I was looking for any available info about fusible links and thought I would give appreciation to jrichker for posting the most detailed FL diagram I've seen. If I am looking for info, and find what I am looking for, in the future I guess I'm not supposed to show any appreciation, which is all I was doing regardless of what thread I was in.

Spaz said:

If previous post is directed to me I apologize. For days I was looking for any available info about fusible links and thought I would give appreciation to jrichker for posting the most detailed FL diagram I've seen. If I am looking for info, and find what I am looking for, in the future I guess I'm not supposed to show any appreciation, which is all I was doing regardless of what thread I was in.

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@Spaz,

In my garage is a set of three chest type tool boxes stacked one on top of the other: it stands about 5 foot high. It is all carefully arranged so that each tool has a place that it is parked and returned to that parking place when I am finished using it.If I wasn't so careful to return each tool to it's parking place, repairs would take forever. I could have a tool for everything on a 5.0 Fox Mustang but never find it when I needed it.

Stangnet is a lot like that set of tool boxes: if it isn't properly organized, it is almost impossible to get help to those who have asked for it. It is much more difficult to chase posts over three or four forums when posts are tacked on to each other with no respect to the name of the person that started the post. I have spent a lot of time here over the past 13+ years to help others fix and enjoy their 5.0 Fox Mustangs. I would hope that others would realize that a little effort to help keep this site orderly is in the best interest of all of us...

Joe R.

I agree, I will be more careful going forward. I do appreciate everything you do to help us. --Spaz

plork66 said:

Bout this 89 with a " professionally installed" alarm that I wasn't to concerned with just figured I would probably remove it eventually, but eventually is now. Had to replace the battery and the next day the new battery was drained. Had the battery checked and the battery was fine. So I started looking for a short beginning with the alarm. I traced every wire from the alarm module and 2 were soldered to the column to the ignition and for power I am assuming. 2 ran into the drivers kick panel and were spliced into 2 pink wires. The pink wires were attached to a plug so I matched the stripes on the pink wires and just hooked them back together. There were wires fished through the firewall 2 went to the alarm siren and a brown wire was spliced in the corrugated flex that appeared to run to the lights. Thought I had everything accounted for. Lastly a brown wire about 18 ga. Came from the passenger side and was spliced into the module, I just assumed the brown wire from the firewall was to be mated with the other brown wire. After reinstalling the battery fired it up I thought I had it, until I hit the headlight switch and the headlights came on and the hatch also released. I then cut the brown wire coming from the passenger side, and now have headlights but when I hit the hatch release nothing. Also my fog lights are not working and the fuse is not blown. HELP

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My experience with most aftermarket wiring has not been good. Anything where someone splices into the factory wiring.

If its done truly professional, then all the connections are soldered and there shouldn't be many issues... I usually find crimp connectors that hold a good connection for a few years, then fail intermittently.

I just went through soldering all my stereo wires. Next is alarm, and automatic window module. My alarm, on the remote entry, the passenger door unlocks and drivers doesn't. Sometimes the driver does, but not very often.

Your aftermarket alarm should be up in the dash behind or around the gauge cluster, or underneath by the steering column. There is probably an starter cut-off relay. Most of their tie-ins should be up around that area. Look for anything that doesn't look original.