The following describes how to bypass the 1995 to current Lighting Control Module (LCM) internal flasher relay on Crown Victoria, Grand Marquis, Marauder and Lincoln Town Car using a standard 2 prong automotive electronic flasher. This is done to eliminate the fast turn signal flash condition experienced when using low current draw LED replacement bulbs in the turn / hazard / and stop lamps.
The LCM purposely flashes the turn signal at a higher rate if the current draw/resistance is below the expected value to alert the driver a lamp is out.
LED's provide extended service life, better vibration tolerance, cooler running temperature, reduced current draw and near instant turn on (beneficial for brake lamps, alerting driver's behind faster)
Even with current technology they are NOT, however, brighter than the stock incandescent lamps in our stock lamp housings, which are designed for the broad light dispersion of an incandescent bulb. So keep that in mind before you decide to switch.
I never cared about having LED lamps so I didn't bother researching a solution for the fast flash condition everyone will experience using them.
After reading a fellow CVN member's solution, which does completely work, I thought there must be a better way that is easy to do.
Some mentioned having the LCM reprogrammed but this is not a realistic possibility, and can't be done even with dealer-level equipment.
It sparked my interest enough to spend a minute looking at the diagram and I found there is a better solution that is even easier, anyone can do, and requires no extra bulbs, pigtails, etc.
I'll start with a diagram of the turn/stop/hazard lamps. This one is for '95-'97 but other than the fuse locations the wiring is the same for what I will be explaining;
Disregard the number and bulbs and such, focus on the multi-function switch. (I have the diagrams for other years in that folder if you want to see your's)
It has 2 power inputs, one switched and one constant. The constant is used for the BOO and to feed the MFS to power the hazards w/ car off. The switched input goes through the MFS, and to the LCM. This is the W/R wire (wire color for the MFS->LCM same '95 to current) and it supplies power for the LCM flasher.
Note the description on the LCM for this wire, flasher INPUT.
Note the adjacent description and wire, flasher OUTPUT.
This is the light blue (color correct for all '95 to current) (flashing) output from the LCM to feed the MFS for turn signal functions.
This supplies ALL the flashing/turn lamps for turn signal and hazard functions.
Now, if you're thinking like me - can the fix really be this simple?
I'll elaborate for those who didn't catch it already.
It's the two wires. Flasher in, flasher out, at the LCM.
One can easily just snip these two wires near the LCM connector, cap them, and wire a 2 prong [b]electronic[/b] flasher (must be electronic, can't be standard thermal. Available at all autoparts stores) right there with two spade terminals on the existing wires. Load side to the flasher OUT wire (LB), power to the flasher IN wire (W/R)
The flashers are still be powered by the same circuit, and will still switch to the constant hot circuit w/ hazards. But, this eliminates the LCM involvement.
Rather than having the LCM pulse the power to work as the flasher, you're just using a standard automotive flasher with the existing wiring and bypassing the LCM.
Here's a quick diagram to show:
I cropped out the rest but what you see in this diagram is applicable for all 1995 to current models (the wiring colors / functions)
Use this diagram for your LCM pinouts to make sure you snip the correct wires:
(05+ LCM pinouts are a little different but the wiring colors remained the same for these two functions)
So, no fast flash when using low current draw LED bulbs. Likewise, there won't be a fast flash warning when any bulbs actually do go out so check them once in a while :tongue:
The important note is to use an electronic flasher. If you use a thermal flasher with the low current it will be an extremely weak flash, if at all. The electronic flasher solves this, and is all of $6 last I bought one. Look for one that says "LED compatible" if possible (some say it)
Does it work?
Well, I got a chance to wire it up and test it. Works great! No adverse effects noted. ;)
So now all you LED nuts have a much cleaner fix for the fast flash :tongue:
Wire it in just like the diagram and use a 2 prong electronic flasher.
I took a picture while I was testing it so you can see the connector and the two wires you need to cut:
As mentioned in that picture, you need to cut the wiring before the LCM connector for your installation. The wiring/flasher setup in that picture was temporary for testing purposes only.
You could use an actual flasher base if you want, but two spade terminals will suffice. Secure the flasher to the wiring harness so it doesn't smack around (just tape it)
Again, refer here for the pinouts for your year:
If you have a '95-'00 you can do a REALLY trick, clean install - our years have a provision for a can-style flasher in the factory dash fuse block. You could extend these wires, pop in the terminals and have a totally OEM-like flasher installation ;)
Email me at dRock96Marquis@crownvic.net
Page last updated: 12-06-2008