Hey you guys mind telling me common locations for electrical problems on these trucks?

 

Anywhere Ford put an electrical connector!!!

 

Most common seems to be the grounds and there is a lot of them to hunt down!

 

Headlight switch and connector is real common, but there is a cheap cure that gives you better headlights, so there is really any reason for it to go bad.

Also this little connector on the passenger inner fender is famous for getting hot and loosing contact.

 

I agree pain in the asst!!!the locks keep breaking on me when i seperate the connectors in the engine area my tps connector is ziptied together!

 

Star, this connector ain't present on his truck, the '87-'91 actually has a rather nice and tidy harness there in place of the snake nest you have in that pic.

Generaltso64, I see that you have an E4OD transmission - water has been known to collect in the connectors where the harness plugs into the transmission, resulting in all sorts of goofy behavior - pull each connector apart and blow everything dry, then pack everything nice with dielectric grease to keep water of for years to come. Additionally what I experience with my truck is the wires for the valve body got damaged where they pass through the plastic retainer plate for the rubber seal in the back of the harness connector on the passenger side of the trans, vibrations and heat cause the plastic to rub through the wires insulation and bare them - some were touching, and one was about to fall apart, I fixed everything then insulated every wire with two layers of heat shrink and finally packed the whole back of the connector with JB weld to ensure no water gets in and no wires move at all. Then up by the firewall under the brake booster there are three connectors that look identical in shape but are different in color (black, white, and green IIRC), these are how the transmission harness connects to the main harness - again pull apart, clean, and grease them.

Now we can move to the headlights switch - Ford really effed up on that one, so install some relays for the headlights, you can make your own harness or you can buy one from LMC for like $30.

Onto the ignition switch - another weak point know to cause vehicular BBQs, replace at first sign of slop in the thing.

 

Thats what I was looking for, ty. Yall keep adding to this post, Im gonna keep fixing as yall post the symptoms im having.

How about the fuel sender grounds (for the gauge)? My back tank works but the needle jumps around...and the front tank Im not sure about because its overflowing full right now. and last but not least, the speed sensor in the rear end be the reason the e4od goes in and out of overdrive between 45-65mph?

 

L cam that pic is not mine. I borrowed it from someone,I suspect someone was having trouble and took the harness apart, there looking for a problem. lol
I see now he has an 89.

 

as far as major issues (think leave you straned or possible fire) LCAM nailed it, as far as major annoyances, all of the ground points, the fuel senders, and gauges.

In my personal opinion, I HATE ford wiring...being that the electrical in these things is so simple (and I have personally experienced these failures usually while traveling, first thing I do when I get one is start replacing wires and adding relays.

Another serious thing to look out for is previous owner wiring....you may find some very "interesting" stuff

 

They didnt start putting speed sensors in the rear ends till 92 I think. On that 89 model is should be in the tailshaft of the transmission unless it's 4x4 then it's in the transfer case.

 

So, can I ground the fuel senders to the frame in hopes that BOTH senders arent bad at the same time?

 

'87 is when the axle VSS came about, but till '92 it was only used for the RABS, the E4OD had its own VSS on the tailshaft like you said. In '92 the tailshaft VSS went away, and the one in the axle drives both the RABS and the E4OD thought the PSOM under the dash.

 

That's what I meant. I should of went a little further with my explanation. Thanks for clarifying that.

 

Even the 89's nice neat connector will have the same problems that the 86 and earlier connector in the picture had.

Given enough time, corrosion will get to all of them, then they overheat and fail.

The grey connector where the engine harness plugs into the chassis harness, the large orange wires on the bottom are the glow plug power wires.
A little corrosion in the connector and it melts.

89 has a connector just like that, with tan or yellow glow plug power wires, and they will melt the connector just like the ones on the 6.9 did.

Headlight wires are to small, relays are the best fix for them to make the lights brighter and the head light switch last longer.

All grounds do need to be serviced, 21 years of weather and corrosion takes it's toll on them.

 

Yeah, that was one of the first things I had to rewire was the glow plug power, along with the main power distribution on the starter relay..replaced the alternator, and cleaned the mlps, and the tps (going to replace them both.)

Does a faulty VSS cause the overdrive to fall out whenever it feels like it?