Mustang MonthlyHow To Tech Qa
Late Model-Corral October 2013 - ’79-’13 Questions
They Call Him Blinky
I own a '88 GT convertible that I have been restoring for several years. I have a minor problem with the fog lamps. When I push the switch, they work for a few seconds, then the lights start flickering. If I don't shut them off quickly, most of my lights go out completely. I checked online and found that the fog lamps and headlamps are on the same circuit and that a bad relay might be the problem. Will you consider a feature on common Mustang electrical problems and how to fix them?
The problem you are experiencing is a long-known issue for the '87 and up Fox Mustang. The issue revolves around a wiring circuit between the headlight switch and the multi-function switch (turn signal switch) with too small a wire gauge to sustain the amperage of the circuit. As the amperage exceeds the wire's capacity, the wire gets hot. As the wire heats up, it loses its ability to carry said amperage and creates more heat, which becomes a vicious circle of more heat and less load capability for the wire. Usually, this only becomes a problem when the OE fog lights are used. Ford admitted there was an issue when they released a Technical Service Bulletin advising the repair of the circuit by running a new, larger gauge wire and taping it to the existing wire bundle. The TSB, 89-17-11, also stated to replace the headlight and multi-function switches and their wiring hard shell connectors if any heat damage is evident.
In the case of your '88 GT, it sounds to us like your issue has become so bad the lights are affected almost immediately. The solution is to inspect the headlight and multi-function switches and their wiring connectors for heat damage and replace them as necessary. A kit, such as the one shown from www.latemodelrestoration.com, makes it easy. Once you have new switches and wiring connectors, your secondary repair needs to either be replacing the undersized wire or bypassing the factory fog light wiring and running them through an aftermarket relay. If you chose to upgrade the wiring, it is the red/yellow striped wire between the headlight switch and the multi-function switch. Ensure your replacement wire is at least 12-gauge and splice it as close to the connector/terminal as possible (or buy new terminals for each connector). It's a little more work, but we recommend rewiring the fog light circuit to take its power through a high-current relay to protect the existing wiring and switches in your dash. All that being said, revisiting these issues with some How-To technical edit is not a bad idea since the Fox Mustang is seeing a resurgence of interest.
Attached is a scan of the buildsheet I found taped on top of the rear bumper absorber foam of my Mustang. The Mustang is a '96 Cobra model with Mystic paint (paint code LF). From under the car, I could only see one of the corners of the buildsheet and it took a while to work it loose without damaging it. The VIN is partially obscured due to the buildsheet getting wet. So, using my buildsheet as an example, buildsheets can be found in '94-'04 Mustangs.
Via the Internet
When Editor Farr forwarded me your email in reference to the July Late-Model Corral letter about S197 buildsheets, I had delusional thoughts of our late-model readers tearing into their cars with wild abandon looking for their "Holy Grail" of a buildsheet (hold the Monty Python jokes folks). At the time of this writing, most subscribers have only had their July issues a few days, so you're our first respondent to our reader query as to whether the '94-'04 Mustangs were shipped with buildsheets intact, either in or on the car. We won't go out on a limb just yet and say they all were, as your Mustang being a limited build Mystic paint Cobra might be a special circumstance. We'll need a larger pool of data to determine if the SN95 and New Edge cars had buildsheets in them when they left Dearborn. That said, we do appreciate you sharing your findings with us and it does offer hope for other '94-'04 owners looking for that tidbit of Ford data.
Let us hear from you. Send your late-model Mustang questions or comments to: Late-Model Corral, c/o Mustang Monthly, 9036 Brittany Way, Tampa, FL 33619, or email us at firstname.lastname@example.org.