So i have been sorting through problems on the old truck 92 f150 5.0 e4od. 2wd. Hook up to bad trailer months ago. Have no blinker or brake on right side. Will light up but never flash and rarely light up i should mention. Hook to same trailer (since been fixed) and now, have a fast left blinker as if a bulb is out. And have right blinker flashing again. Only with trailer though. Newer problem is that when i had my lights off all was ok. Was cruising at about 70 and turned on my marker lights, rpm skyrocket about 400 rpm. Shut off lights and they drop back down. Left blinker does the same. Right does not. I am puzzled. Where could my issue truly lie? I have not messed with this in a while now. But not understanding how this is happening on and off.

 

I'm gonna go out on a limb here and guess you have LED taillight and front marker bulbs in the the truck and maybe the trailer, too. These don't present enough load to the system, making the PCM think a taillight is out. When the brakellight element segment is supposed to be on, the PCM unlocks the torque converter, causing the revs to go up. You need load resistors in the brake light sircuit to counteract this issue. Also, no flashing on the right may be a fried combination (turn signal) switch, scorched by that bad trailer wiring.

And, if you didn't have LEDs, nevermind my rambling.

 

there are no led in the tail lights. That does sound like what its doing though, unlocking the converter. So maybe a fried bulb and turn signal switch. I will look into that this week when my door cable and window motor cone in

 

So, you're cruising at 70, turn on the lights, rpms go up by 400 rpm. That sounds like the TC unlocked on you. Same with the turn signal action with the left turn signal.

These trucks will unlock the converter if it senses no or not enough load on the brake light circuit. Not sure how the running lights would affect the TC, though.

Fast flashing is caused by too much load on the conventional style non-mechanical or non-solid state flasher. So, left side flashes fast with trailer, I can see that. light duty flasher can't handle the load of three bulbs (trailer, brake light, front marker light). No flash right side w/o trailer, flashes somewhat normal with trailer on the right seems to say burned out brake light or front marker on the right side of the truck.

To help us diagnose this, what was wrong with the trailer that started all of this?

Also, have you checked all fuses and lamps?

 

all fuses were good, i have no brake on right side. Trailer was damaged from my dad, had some damaged wiring and a broken lamp on r side.