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View Full Version : Tail Lights, Instrument Lights, Parking Lights NOT working



MercuryZephyrZ7
01-26-2014, 12:33 PM
Hey all,

Im a fairly new member here, been lurking for a while learning a lot and bought my first MM back in November (Told my new bride I needed a bigger 4-door for the baby coming hah).

Anyways, Ive searched and saw a few threads with similar problems but none of them seem to offer much of a solution for me. SO...

When I bought the car one foglight was broken, and still is. They have never worked so yesterday when I was doing some fluid changed I decided I'd throw in a couple bulbs and see if they work. Well they did! And I was happy. So I went about the work and aftwerwards washed the car. Thats when things changed.

After the wash none of the above mentioned lights worked anymore. I still have brake lights, headlights/high beams, and turn signals. No tails, instrument, parking, or fogs anymore. The little light on the Headlight switch doesnt light up for the fogs anymore either. I Cheked the fuses and #21 was blown. I replaced it and it blew immediately again and again.

WHAT IVE DONE: Checked the wiring above the visor which was in good shape. I checked for a short in the tail light harnesses but found nothing. I switched my Foglight relay #207 with #209, then put in a new #21 fuse and it blew immediately again. So that didnt help.

My thoughts are as follows: Possibly after putting a good bulb in the broken foglight housing, then it getting wet may have done something...OR...I have a bad headlight switch. I dont suspect the LCM because my turn signals work. I ensured the plugs were seated on the back of the LCM as well.

Im skeptical it's the headlight switch too because the fuse keeps blowing, and if the switch was bad I would think the fuse wouldn't blow and just nothing would work.

The headlights come on at night in the Automatic position without tails, and they come on when I turn the switch all the way to the right, also without tails.

Im not sure what else to look at and Ive tried to include all of the info I can think of. Any help is appreciated, you all probably know a lot more about the electrical system on MM's than me at this point. Thanks!

fastblackmerc
01-26-2014, 02:27 PM
After you washed the car the foglights blew fuses..... you got water into the foglight system somewhere. LCM, switch, relay etc. have nothing to do with the problem. Did you make sure the bulbs were fully seating in the foglights? Where they locked in (1/4 twist counter clockwise). Are the two connectors at the bulbs and harness fully seated?

I would disconnect both foglight harnesses at the harness - not the bulb.

Install a new fuse.

Turn on the foglights (NOTE: the key must be in the RUN position)

Plug in one harness

If the fuse blows the problem is on that side

If the fuse doesn't blow, connect the other side.

If the fuse blows, obviously the problem is on that side

MercuryZephyrZ7
01-26-2014, 03:07 PM
Brilliant, I knew someone here would have something in mind I hadn't tried yet. The sockets are fully seated in the housings and the bulbs were fully seated in the sockets. I have since took the bulbs out so the sockets are just in the housings with no bulbs.

Ill get out there and try that now and post my results afterwards. Thanks.

MercuryZephyrZ7
01-26-2014, 03:31 PM
Well I guess it won't be that simple :/

I went out and unplugged each fog light at the plug near the edge of the bottom of the front bumper. With both unplugged I popped a new fuse in and turned the key to "On" with the headlight switch in "Automatic". The fuse blew right away again.

I then pulled the fog light fuse in attempts to bypass the whole system for the time being and tried it again but the #21 blew again.

MercuryZephyrZ7
01-26-2014, 06:35 PM
****FIXED****

So the solution to my issue actually ended up not having anything to do with the fog lights at all. After cleaning the fog light sockets and connectors the fuse still blew, so I didnt know what else to do but try to clean the rest of the sockets.

I pulled the tail lights out and cleaned the sockets and THAT ended up fixing the problem. I used CRC electrical cleaner (in the spray can) and it worked like a charm. Now all is well and everything is working just as it should. Thanks for the tip Fastblackmerc, I appreciate your knowledge and willingness to help.

fastblackmerc
01-27-2014, 12:56 PM
Glad you were able to find and fix the problem.... electrical problems usually are a B***H!