My '99 F150 is experiencing an ongoing bunch of electrical issues that started with the left rear turn signal not working. Since then I have found several issues that have fixed that problem but now my right brake light and rear turn signal have quit.

During the course of all the problems that I had I found a loose wire in my multi function switch, the connector for the tail light harness was partially disconnected and several questionable splices done by previous owner.

But with all of that taken care of I now have the right rear brake light and turn signal not functioning. On top of that (and I don't think these are related) the compass and thermometer in my rear view have quit and my cruise control is dead. All of this worked prior to a week ago.

I have checked all of the grounds and have traced the wire (Or/Lt.Blu) for the brake light / turn signal and it has no power as far as I could follow it forward. I think it goes up into the power distribution box but I'm not certain.

There is a problem in the PDB at fuse #19 but that is for the trailer brake/ TS circuit. It shouldn't cause the problem I am having (or could it?) I did apply 12 volts to the PDL plug in #19 with fuse removed and the brake light and turn signal worked. Is that normal?

I hope that someone can steer me in the correct direction. My Haynes manual doesn't have a complete wiring circuit.

Thanks,
John

 

John,

The FIRST thing that you need to do is to buy the correct Ford factory service manual! At least buy the one for the electrical system. They can readily be found on E-bay and the price is reasonable. I've been taking care of all of my own vehicles for about 50 years and I NEVER seen a third party manual that was worth owning. Not even the Bentley Z3 manual that I paid about $100 for! Aftermarket manuals are even worse when it comes to electrical systems! I had one for a 1970 Dodge and the electrical diagrams in the manual clearly said that they were for a 1966 model!

"and several questionable splices done by previous owner."

It sounds like you're in for some work! If the PO couldn't even make decent splices, well there no telling what else he may have F'd up! I think that you're really going to need a GOOD electrical manual! Sorry but there's just no easy way to figure out what all may be wrong! Especially when an incompetent DIY'r has been into it! You're just going to have to grind through the problems one after another until you find and fix all of them. The only suggestion I can make is that if one problem is too hard to find, drop it and go work on the next one. I've found that often, I accidentally find the source of a difficult problem while trouble shooting an easy one. So try to work on the easy ones first, you may get lucky.

 

That wire goes to the MFS.

Yes, that's normal. Backfeeding F19 provides an alternate source of power to the Rt stoplamp/turn circuit.

Go back to the MFS and find that OR/LB wire. It and the LT Grn/OR wire (Lft stop/turn) should both go hot when the brake is applied or should pulse when the emergency flasher is operating.

 

My 2006 STX developed the same problem several months ago. I didn't investigate it because I'm lazy.
A few weeks ago, I started to look into it and I replaced the parking brake sensor. The P-light stayed on.
The local parts store wanted 40 bucks for the master cylinder sensor but I found out that you could tap
the dash and the P-light would go out and would eventually come back on. This morning, I followed this
thread's instructions but I used a 1" x 2" rubber foam in between the plug and the gauge housing and the
P-light went out. Put everything back together and drove around and the P-light was out.
Thanks to all of you F-150 owners.

 

The popping started a couple of days ago Which I don't understand I have new lower And upper joint And lower ball. joint , Wheel bearing hubs acti Is actuator , CV axles and new sway bar links so I have no Idea what's going on?

 

1. You posted this in Electrical Systems in someone else's thread. Start a new thread in the correct forum.
2. Please provide full truck details, we can't see it through the Internet. Describe the problem with more detail.

 

did you ever end up figuring out what the left harness does?