I installed Depo L style lights in my 1999 f150. everything worked fine until couple months later. The high beams flash whenever the left or right turn signal is activated. Both dash turn indicators flash as well. If i turn the main light switch on the high beams are on steady, but when i move multi-function switch to high beam position, the headlights go out completely. And on top of that, when i push the button to activate the windshield washer, the high beams come on, and the washer pump has reduced power. Though it was the MFS for sure, but it does the same thing with brand new MFS. Anyone run across this before? Can the Depo lights cause problems?

 

Sounds like a wire or 2 are lose or broken off the MFS. It has to be in the steering colume somewhere. I have seen the headlight switch go bad to, but this has to be around the MFS.
Lariat#1

 

Try moving the steering wheel up and down then you are testing, to see if the problem goes away.

This is testing the connector in the steering wheel column, to see if it is pulling apart.

While this usually solves problems like no turn signals, or brake lamps, I would not want to rule it out that it can cause other problems.

The Depo lights should not be causing any problems, as long as they were a direct replacement for the factory lights ( used std bulb connectors, no splicing or change to the factory harness ).

 

The Depo projector lights came with a wiring harness that plugs right into the factory harness on the passengers side which is used as a "signal" to control relays. The relays and Depo lights have their own wiring direct from the battery. Some guy at the ford dealer thinks i may have fried some wires, but i cant see how using the factory harness to control the relays would overload the factory lighting circuit. when i originally replaced MFS i noticed the top connector had most of the terminal locking tabs broken, so i changed the connector.The other connector is fine. I have tested the main light switch, which is ok according to service manual. I have tested the MFS harness (which runs on top of column to just below) for opens and shorts. I dropped the fuse box, peeled off tape and inspected the wires going right to the Central Junction box, nothing appears burnt or chafed. It still does the same problem, with the MFS just plugged in and not bolted down. Any other suggestions guys? Thanks

 

considering you had 2 changes ( connector and wiring harness addition ), best to go back to stock,and make sure the connector change out was good.

remove the aftermarket light harness, and return the headlamps back to factory, and test again.

if the problem persists, you have a problem with the connecotr change out you did, if not, it is the aftermarket wiring,

 

i had had the DEPO lights in my 97 for a while. back when i bought them, they didnt have any wiring harness included. but since i bought another set of lights for my lightning (same as the ones on my 97), i saw the harness they included. personally i dont like it. i like the one that i had made. i dont like the idea of sharing the signal setween the two lights...which essentially is what the harness they include does. once it get's warm out im going to hack that harness up & install it just as i did the install on my 97. 2 years and no problems.

 

Thanks guys, for the suggestions. I unplugged the after market harness and plugged the stock lights back and noticed that the right light was dim, flashed with the turn signal, and the park lights in the front were dim. The front left light was fine, bright and unaffected by the turn signal. I went to ford and photocopied all the relevant pages out of the wiring manual. I discovered that the right headlight, front parklights, front turn signals and windshield washer pump all share the same ground, which is to the right side of the rad. I disconnected the ground, stripped all surfaces down to bare metal, reconnected the ground, and everything worked normally after, even the depo lights. Electricity will take the path of least resistance, it couldnt go thru the ground so it was backfeeding into multiple circuits, appearing as a short between circuits.

 

Thank you for posting the solution to your problem.

Too many times this does not happen, so some search topics are useless.

Glad everything is working well for you again

 

Excellent!