Blinkers work fine without head light switch on. With head lights on the left blinker blinks fast all bulbs are working, even both back up lights are in the mix. Where can I look or get a wiring diagram?

You obviously have a bad connection somewhere in the taillight. Some trucks it is a common problem and the taillight circuit board is the problem.

check the ground wires to the rear lights sometimes the head lights will provide backfeed ground when off but cannot when on this would explain the rapid flash

most blinkers uses relays, and when they flashes fast one light is out, but you replaced your burnt bulb might be a bad relay.

Check the switch

mporteous, It sounds like you have a light switch problem. I can't think of any other reason for the running lights and tail lights not working in this situation. Are your brake lights working when the headlights are off and how about when they are on? Do your four ways hazard lights work in these situations? Try all the lights under these conditions. The reason the left turn signal blinks very fast is because one of the bulbs are burned out. Try the left signal and one light (front or back) will stay on and the other will not come on at all. Replace the bulb that does nothing. Do this before you try all the lights in different situations. I think that you will have to replace the light switch. Good luck with this.

Bad ground, or check all your bulbs. Usually its a ground in the back of the truck under where the spare is. If its not the ground check the bulbs. Please rate Thank you

start by looking for a bad ground to one of the light sockets

Everything works, more or less, so you know that the switches and fuses are good. That means that you've got either bulb problems or power/ground problems. First, try swapping the bulbs around to see if the "bad" lights will work with the known "good" bulbs in them. If so, you just need to replace some bulbs. If not, check the sockets inside and out for corrosion, clean them (wire brush, steel wool, sandpaper, etc.) if necessary, and use a voltmeter or automotive tester to make sure that you have power and ground to each socket. The fast flash on the turn signal is just an indicator that a bulb is out.

Bill B

You have a bad bulb, ck for a burnt out bulb one the side of your head light assy. 

Usually a fast turn signal means that there is a light out. You should probably check all of your lights, including back-up lights, and turn signals. If there is one out then replacing the burnt out bulb should fix the problem.