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Rear indicator,hazard and brake light not working, but front are


jorg01
09-11-2014, 12:20 PM
My Fords left rear indicator, hazard and brake lights stopped working 3 weeks ago, front ones are fine and blinker blinking faster. Now my right rear indicator, hazard and brake lights too stopped, front ones fine. Bulbs are fine , connections seem fine, this is a strange one, want to avoid expensive trip for diagnostics. Any ideas or anyone with same issue? Thanks for the help.

shorod
09-11-2014, 01:27 PM
Does your Explorer have aftermarket trailer wiring installed that was spliced in? I've seen on several occasions aftermarket trailer wiring that was not sealed properly from the elements and caused taillights to stop working. The fix often requires replacing several inches of wiring per line and using adhesive lined shrink sleeving or F4 self fusing silicone tape to properly insulate the connections and splices. The Explorer should have a trailer wiring connector in the rear and not require splicing. The harness costs a bit more at the time of purchase than a universal one, but will generally save money later in repairs....

If there is no evidence of modifications to the wiring in the rear then you might find a problem with the multi-function switch (MFS) or related connectors/wiring.

If you have a test light or multimeter handy, check in the area of the left rear taillight, from underneath the vehicle, for a circular connector with a rubber cover. Pull the cover, turn on the hazard lights, ground the test light/meter, then probe the contacts checking for a wire that flashes at the same rate as the front indicators. If you find such a signal, chances are pretty good the problem is not with your MFS but rather with the wiring. If you don't find one that flashes, the problem could be the MFS. I'll have to check the wiring diagram to confirm the front indicators are on a separate circuit through the MFS from the rears.

What year is your Explorer, and what model is it (Sport, Sport Trac, or standard)?

-Rod

jorg01
09-11-2014, 03:29 PM
it is a ford explorer standard 2003, ford told me the multifunction switch controls both front and rear together, so i am not too sure. but am willing to go get one anyhow.

shorod
09-11-2014, 11:41 PM
According to the Ford factory service manual for the 2003 Explorer, what the dealer told you is not correct. The MFS has a separate set of contacts for the front left and right and the rear left and right. The rear left and right are spliced in to the trailer tow relays in the battery junction box.

If you want to diagnose the MFS rather than shot gun it out, open up the battery junction box and see if the left and right trailer tow relays are installed, or if the terminals are at least populated. If so, turn on the hazard lights and probe terminal 1 of the relay socket for a pulsing voltage which would correspond to the flash rate of the hazard lights. If you get voltage here, the MFS is NOT the problem. However, if you do not have flashing here for the rear yet the fronts are flashing, there's a good chance the issue is the MFS.

-Rod

jorg01
09-12-2014, 05:54 AM
Thanks, will try it this weekend, would the mf switch be the problem if first rear left and then 3 weeks later rear right stop working?

shorod
09-12-2014, 07:49 AM
The left and right are two separate sets of contact in the MFS, and similarly 2 separate sets of wires going to the rear taillights. So the timing could be coincidence or the issue could still be in the wiring.

If you have an aftermarket trailer wiring plug that's spliced in to the taillight wires instead of taking advantage of the pigtail connector Ford provided, there's still a high likelihood that's the issue instead of the MFS. And if that's the case and you can confirm you have hazard/signal pulse to the relays, then it becomes the more likely scenario. The test at the battery junction box is a test to help you determine which direction to start looking - between the relays and the turn signal stalk (including MFS) or between the relays and the taillights.

-Rod

jorg01
09-14-2014, 06:06 AM
Thanks, we will try tonight after work.

jorg01
09-14-2014, 08:35 PM
hi, surprizingly no luck. It was not the switch, the wiring at the trailer attachment is working an there is power at the wiring of the bulbs at rear. Any other suggestions before I nee to take the car in to be serviced?

shorod
09-14-2014, 10:40 PM
Did you plug a trailer in to confirm under load they work fine? When testing at the rear bulbs did you use a multimeter or a test light? At the bulbs did you confirm the bulb ground is good to vehicle chassis ground?

If you didn't have a load on the trailer wiring or bulb sockets you could have a high resistance path in the supply but once you load the circuit, insufficient current can pass to light the bulbs. Since a multimeter has a very high input impedance, it's not good for testing lighting issues other than for measuring continuity. An old school test light with a bulb (versus new LED lights) will usually provide a sufficient load to really determine if enough current can pass.

-Rod

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