I have a late '99 Navigator, with the 32V engine. I am having problems with my high beams blowing the fuse. I have had a shop do the work on it so far, but they seem to not be able to locate the problem after three or four tries.

For them, it always comes down to the MFS being shorted out, or terminals melted away, but this is only a high beam problem. They have found the contacts on the MFS melted, and say it is just not up to the task, but it did fine for about 150k before this problem started. they can replace the MFS switch, and all will seem to be fine. i can run the high beams for hours. I may be able to use them several times for short times too. but sooner or later, I am going to switch them on and "nothing happens"- no high beam headlights. Blown fuse.

I am using Sylvania Silverstar lamps, but I believe this problem started earlier. I not they are marked with the same wattage as the OEM lamps.

As for front end damage, yes, it was in a slight crash that did not cause anything but the bumper and bumper cover and one fog light to be replaced. None of the wiring was even compromised.

My thinking is there is a short where the wiring harness goes through a bulkhead, like the firewall or the core support, or something like that. I had that problem on an old '89 F-150 where all the dash gauges went nuts due to the wires being cut on the sharp edge of the firewall where they went through.

Either way, I am wondering if any of you have had this problem?

 

Which fuse?

Which Silverstar and what wattage are they rated at?

DRL equipped?

Autolamp equipped?

Need data to identify proper diagrams.

When they fail, does the "flash-to-pass" feature still work?

Steve

 

OK, here are the answers:

 

try hooking up an ampmeter and see how much power the lights draw; try turning them on and off several times, jigle some wires, etc. take note of the power draw. could be a loose wire causing a periodic short. a nick in a wiring harness can be hard to find... on high beams you should be getting 9-13 amps for both lights at once...

the older model fords (80's) didn't even have fuses on the headlights for safety reasons...

keep some spare fuses handy!

 

Joe's pretty much covered what I would have come up with.

Calculated high beam current should be around 9.0 - 9.5 A with engine running, well within the cpapbility of a 20A protected circuit.

I'd also suspect a nicked or chafed wire. If you can't induce the fault reliably, you're left with either inspecting every bit of wiring or to inserting inline fuses to isolate the portion of the circui that is shorting to ground.

Keep in mind that the high beam circuit also goes to the cluster for the indicator, so that will also have to be kept in mind.

Here's the electrical diagram if you need it: 1999 Navi Autolamp.pdf

Good luck, you'll likely need it along with some persistence and hard work.

Steve

 

Thanks for the help guys. That is about what I had figured as to how to locate the short.

I had only hoped this might be a somewhat common problem, since the F-150, Expedition and Navigator share so many parts and general chassis design, and someone could tell me to look there first, if there was a known problem area.

My 89 F-150 was known to eat through the wiring harness at the pass through in the firewall, which it did. Pretty easy fix once I knew where to look.

This one... I know both me and the shop are frustrated by it.

As for the amps, are you saying "X amps" for both headlamps? Or for each lamp?