I have a 1990 F150 and recently ran into an electrical problem. The ignition switch ( the one mounted on the steering column) fell apart. The bracket part was still mounted on the column, while the ceramic connecter was still plugged into the harness. I changed the switch,and anything that is key activated, is still completly without power. Headlights,tailights,and hazzard flasher all work, but the instrument cluster,turn signals, radio, and heater won't. I've checked all the fuses,which are good. I've traced all wires from the solonoid through the firewall and up under the dash, and found everything ok, and all the fuseable links I came across look good. And when I first discovered this problem originally, I had no power at the key.( At first I thought someone stole the battery, then discovered the bad switch)) So far I've changed the ignition switch, the key lock cylinder, the EEC, and believe it or not the seat belt buzzer. ( which also doesn't work) There is a black wire w/ a pink stripe that leads from the contact at the key lock cylinder to the seat belt buzzer, I thought that maybe it was the problem, but I thought wrong. Is it possible that when the switch fell apart, the contacts shorted something out? Anyone with an idea as to what my problem may be, or what else I may need to check, any answer would be greatly appreciated. This is driving me nuts!!

 

Do the Yellow wires at the Ignition Switch have power?

Why did you change the EEC?

 

I changed the EEC because of a buddy of mine's ill advised suggestion. I just checked on the yellow wires ( there's two of them coming off the switch) and no, neither one has power.

 

The Yellow wires feed the Ignition Switch power.
You have an open Fuse Link in one and possibly two places.
One is the Fuse Link(s) feeding the Yellow wires (sometimes black with an orange stripe) at the Starter Solenoid on the hot battery cable side.
Also maybe there is a Fuse Link in the wiring harness about a foot or so from the firewall in the engine compartment.

I do not have an exact wiring diagram for a 1990 so I am not 100% sure on the colors and if you have the second fuse link or not, I know the 89 E-series does.

 

I'll check it out and keep you posted. Thanks!