My name is Gran, I have an 08 Ranger 3.0L Recentky I went out to start my truck and it was running real rough and the brake lights were on but dim. I revved the engine for a while and it went away for a few days. After a few days I went back out after work and it started again. I noticed that when the key is on the blinkers work fine but when the engine is running the blinkers flash fast, the brake lights stay on dim until I turn on the parking or headlights then the tail lights don't light at all and the engine runs rougher. I replaced the fuel pump, crank sensor, cam sensor, both upstream O2 sensors and I have checked every ground on the truck. I have even swapped out the battery and checked the alternator. Getting ready to swap the ECU. I am stumped!! Any suggestions other than buying a new truck?

 

Welcome to the forum.

Not alot to go on but weak lights and slow blinker with engine off means battery voltage is too low, that could be the battery itself or the connections from battery to vehicle(battery cables).
People often check positive battery cable but not negative, both need to be clean connections for system to work properly

Car battery voltage should be 12.3 to 13 volts engine off.

Engine running, alternator working, should show battery voltage at 13.5 to 15 volts

Under 12 volts with engine running means alternator system is not working and engine can run rough because spark voltage is too low.

Turning on head lights drops voltage even lower and engine runs rougher.

So it reads like you have a charging system problem.

You don't mention the Battery Light in the dash?
Is it on with key on, so you know bulb is good?
And is it off after engine starts?

Check fuses #9(5amp) and #10(10amp) in cab fuse box, these "turn on" the alternator


Ford started using "smart charging" which means battery used should be silver calcium type, not standard lead acid type.

Test battery voltage with engine off and then with engine running
If they are close to the same then, unplug the 2 or 3 wire connector on alternator, smaller wires not the big wire
Check battery voltage again
If voltage is higher now then shut off engine, not good to run it this way.
Trace the 2 or 3 wires back to ECU they are probably damaged
Not an uncommon issue

Video of damaged control wires here: www.youtube.com/watch?v=lucj_ALV5M8

 

Good luck with your ride!

 

Something similar happened to me but not on a ranger. I had developed a small exhaust leak which had melted a cluster of wires together. Check all the way from your exhaust manifolds back and see if anything has been fried. If the motor starts without jumping it there is nothing wrong with the battery or charging system. The ECU is not the problem save your money.

Check the ground strap between the chassis and the motor I don't have your exact truck so I don't know where they put it on yours. I do know there is one more between the bed and the frame that will affect tail lights mine was busted.

 

Wanted to thank you for the replies. I checked everything on this truck. Voltage was good,alternator, all grounds etc.. It even had my mechanic baffled. When the truck was running the blinkers flashed fast like there was a bulb burnt out, when you stepped on the brake it would flash normal. After running it with the blinker on I found a bad connection in a harness that came through the firewall and connected under the steering wheel. What a load off my mind!!!

 

Good work finding that

Thanks for the fix info