Bounds and solution to electrical failure in a 2004 Grand Marquis

Question

What follows is a simple problem with hopefully a simple solution. While mechanically-oriented, vehicle repair is not my specialty, so forgive me for any lapses in problem description and terminology.

I currently own a 2004 Grand Marquis GS, inclusive of the factory and owner manual. My immediate family owns a second model year of the same, with a similar reproduction on this issue, so I know it isn't isolated to just my vehicle.

That issue is simple: at interval, the car's electronics will completely cut out during ignition. In these cases, sparse or no power will be available to other electrical components, and the ignition may be left spinning unless the vehicle brake is depressed.

I'm aware of the basics of how the system operates (that is, it's an electronic ignition, where and how my battery operates, how the Lighting Control Module (LCM) connects, et cetera), but I'm unsure of the current scope and correct fix to this problem.

Specifically, I need to know the following:

• Is it safe to operate my vehicle in this state? That is to say, is this isolated to and only to the ignition sequence?

• What steps should I take to troubleshoot or provide more information on this issue?

• What steps should I take to fix the issue? More concretely, if the answer is to replace fuses, the battery, or some specific subcomponent or module, I'm competent enough to be able to do that.

I've found this thread on LCM repair, but because this otherwise isn't my area of competence, I'm unable to make easy sense of the information provided. I can, however, make sense of the service and user documentation, and I should be competent enough to make small repairs. Anything larger than a few modules or that requires a dash teardown is going to a professional mechanic, however.

Thank you in advance for your time and thoughts on this. If I can provide any additional information to help here, feel free to ask away in the comments.

Answer 1

Simple problem, simple fix. Popped the trunk, discovered the cathode terminal on my battery was corroded over (which I wouldn't have taken as a warning sign before asking for help). It turned out that, even after flushing off the damage, my six-year-old battery had finally gone bad.

I verified this by watching the performance of other electrical components in the vehicle, noticing dimming and other warning signs of a failing battery. I also queried the symptoms to the peanut gallery on Twitter, and the overwhelming response was "bad terminal connection or bad battery."

After purchasing a fresh battery and lugging it a few blocks, dropping it in fixed the issue. I would speculate that the electrical components would have remained in a shoddy and inconsistent state had I not done so, and under those circumstances, the vehicle would indeed have been unsafe to drive.

I'll leave this here as a signpost for others running into the issue. Battery-bound, erratic electrical failure is a common enough failure case that others might benefit from reading about it here.