Ford LCM Issue?

[Falcon_LS]

More of an electrical issue than mechanical, but I'm facing a bit of a strange issue with the blinkers on my '01 Grand Marquis. There are zero issues with the turn signals when the lights are off, but if the lights are on, either automatically or manually, I have a hyper flashing issue. When you first turn on the blinker on either side, it'll flash normally for a second or two then start to hyper flash. No issue with the hazard flashers, none of the bulbs are out and I don't have LEDs or anything.

Not quite sure where to start with this one, and quite hesitant to dump crazy money on an LCM if it isn't the culprit. Any input will be appreciated, thank you!

 

[Colt45ws]

I suspect a ground issue. The headlamps and turn/park on the front all share a common ground along with a TON of almost everything else in the engine compartment, ABS, wiper motor, etc. Its G102, Right hand front fender, centerish.. I would check the voltage at the ground pin of the front turn signal bulb with headlights on/off compared to at the battery. If its significant, that is your issue.

Same thing at the back, all the bulbs share a ground, G400. Its at the rear of the trunk, center, right be low the latch. Youll need to check for voltage drop at the bulbs there as well.

 

[Falcon_LS]

Thanks, Colt!

For the front, is that the one behind the washer fluid reservoir?

 

[Colt45ws]

Negative, its by the battery. The battery has its own ground bolt on the fender, and right below it is the one we are talking about. Comes from the harness leading to the battery fuse box.

It looks like the engine fan also grounds there. I bet you run the a/c all the time and hence the fan is always running. You might test it with the a/c off and the fan motor off to see if that changes anything. If so, that would eliminate the rear one as being the problem.

 

[Falcon_LS]

Gotcha, I was thinking about the other side. I'll take a look at that and report back.

 

[Johnny2Bad]

Hyper flashing is built into flashers to tell you something is not right, usually a bad connection at an automotive connector or a burnt out bulb.

It could potentially be a ground wire, but usually all the lamps share the same ground, so if the side marker lamps at that corner are working (for example) the ground is good up to the lamp module or nearby connector. First thing to try is to remove the back of the offending lamp (usually pop-off plastic) and clean everything up with a suitable cleaner (I use home-made Windex*, but anything that doesn't leave a residue is fine).

* Home-Made Windex:
1 ounce household ammonia, two drops (no more, no less) of liquid dish soap, fill spray bottle with water. I add a drop of blue food colouring so I can easily identify it as a Windex substitute. If it really matters to you, you can add a drop or two of a liquid scent so that it doesn't smell like ammonia, but I don't.