'88 7.3 F-350 w/automatic trans. Got the engine back in. Running good. Tag went out while I was working on it. Got to pass inspection to get it back on the road. In checking everything out I found a blinker problem that has me baffled. Turn the right blinker on and it works fine. Turn the left on and both left and right come on, fount and back. However the right is not as bright as the left and not as bright as when as when I have just the right turned on. Also the cab over lights flash on and off like as if I have my four ways on. Also I hear the flasher on the fuse box making and on and off thud sound. Sounds different then it does when the four ways are on. When I turn the right on I hear no noise. I've change out the little round flasher on the fuse box. No change. Check all my grounds. They are all polished up now. I polished a spot on the bed and the frame with a four inch grinder and put jumper cable to in the increase the ground. No change. Disconnected all lights including the cab one ones and tested each one at a time. Nothing. I've removed the steering wheel pulled out the blinker switch. I haven't disassemble or disconnected it yet. It's held together with a push nut. You can't remove them things without destroying it. Had to first make sure I had a replacement. I got one now. I can take it apart tomorrow and clean and polish it's inside connectors . I don't know if I'm on the right track. But that's all that's left I can think of. If it needs replaced I would like to figure out that is the problem before going and buying I new one. Thought I would check with you guys to see if anyone has any thoughts?

 

When you are checking t/s do you have tail lamps on?

 

That sounds pretty definite. I had read talk about the cam. But I didn't know what part that is. Looked it up. That's the white plastic part held on by the press nut I was talking about. Looks like it's $25. I had forgot, ever since I bought this trunk in 2009 I've had to jiggle the turn signal rod after turning on the turn signal to get it just in the right spot to work. So I'm just going to replace the whole switch which is $55. Might as well while I'm in there. Hopefully I won't have to go back in there again. Thanks for the help.

 

Might be low on Blinker Fluid.......LOL

Here is a YT Vid.


Charlie

 

Update. I replaced the turn signal switch. Hardest part about that was pushing the two plug ends back together. That was a bear. Sad part is it didn't fix the problem. While I had the dash apart I noticed that also the dash illumination lights were flashing too. If I turn on the parking lights or headlights all flashing stops. Course I'm still talking with the left turn signal on. I thought maybe it's a bad headlight switch. Got access to it and checked for voltage with the switch attached, Two poles were flashing the test light. Removed the switch and found the problem still exist. All blinkers and cab over lights flash with the left turn signal on and no head light switch attached. Checked the headlight plug with the switch removed. Found the only one flashing is the wire in the center. A brown wire that goes to the dimmer. Course there is no flashing when the right signal is on in any wire in the plug. Guess I need to find out where that brown wire goes. I don't have a wiring digram. Is there anybody that can tell me where it goes or what else the check? Is there a place where I can see a wiring digram?

 

Sounds like a ground issue even though you have looked at that. Have you pulled the bulbs and checked the fillaments? I have had a few over the years that when one breaks it will make contact with the other which then causes a backfeed issue and gives the results you are having.

 

I have found a wiring diagram on here for a 1990 F-250. Would mine be the same? It shows a 'Muti Function Switch'. Seems anything goes thru it. Do I have such a switch? If I do, where would I find it?

 

Yes, I have checked all the bulbs and grounds to the bulbs. All are OK. I have disconnected all the lights together that are coming on with the left signal and one at a time. With all the bulbs disconnected except for the right front, the right front still blinks when the left turn signal is turned on. Same for one at a time. I also have a Tommy Lift on it. It has only one wire, the Hot wire the size of a welding lead, going to it. It is grounded to the frame. It works fine. So the frame is well grounded. Well, it's actually on the bed. The bed gets its ground from the frame. So all is well grounded.

 

I have found none flash at all if I turn the tail lamps (parking lights) on. But still If I turn the right turn signal it works as it should with the tail lights on.

 

Multi-Function Switch is turn signal switch.
All the blinker and brake light filaments get power through it. When ot gets worn out, it'll cause all sorts of foolishness.
Reading through this thread, I feel Multi Function, bulb sockets, and grounds are messing with you.
Also, as a reminder to all, LED bulbs need load resistors connected in parallel to them. Especially brake lamps or RABS will set a waring light on the dash and become non-functional.
So start with fresh bulbs, clean up sockets, follow and clean up wiring, then check / replace Multi Function switch.
Don't overlook where the wiring runs into cab by steering column on engine compartment.

 

So what is this? This is what I found that makes the sound I mentioned earlier. It was mounted on the inside of the driver side fender. Has five legs in it. I removed it and no more sound. But no change in the flashers either. Maybe there is an open circuit in it that is supposed to close? All I know is it makes the sound (more of a thud sound) when the left flasher is on. No sound even when you put it to your ear when the right flasher is on. Removing it had no effect on my problem except no more sound. Sorry for the size. I haven't figured out a way to control that.

 

I find the sound to be more of a clicking noise now that it is not mounted to the truck. Guess the fender was kind of like amplifying it. There are no LED lights on my truck. The tail/stop lights are more like trailer lights since it is a custom bed. I have a new Mutifunction/signal switch. No change with it. So that rules that out. Also I've noticed with the left TS on the tail light the flashing is going thru the parking lights. Not the brakes. Same with the front, going thru the parking lights. Not the filament that should be the TS.

 

That's a relay for auxiliary lights.
It's an option to control extra running lights, trailer lights, etc, and it's activated by the basic non-option circuits.
I'd leave it out for now, go up and follow harnesses on drivers side frame rail up to cab.
There are at least 3 harnesses:
Fuel Tank (and tank valve if you have 2 tanks)

RABS valve (if you have Rear Antilock Brakes, valve is inline with rear brake line on frame) also a sensor wire(s) to the top of the rear differential.

Tail Lights

I bet somewhere you'll find the tail light harness messed up.
There should be:
Tail lights
L brake/stop
R brake/stop
Backup Lights

Thing is, if anything is miswired, stuff like that relay will be activating when it shouldn't
Put a real-world test light on each of those and test function and ID them
Also, if you have a trailer light socket, it'll do weird stuff if it's shorted

A DVM is too sensitive and doesn't present enough load to properly test the whole circuit.
I would actually use a Tail light bulb or at least an incandescent tester to do this.
Keep in mind that it takes the full load of a pair brake/turn signal filaments to make the flasher work properly and it won't flash at the proper rate if a front or rear bulb is disconnected or burnt out

 

This truck never had a standard bed on it. Ford shipped them down to North Carolina where custom beds were built and installed. At one time it had a strobe light, work lights and lights for inside the tool boxes that are under the bed. Those are probably the reason for the auxiliary relay. It's an 8' by 12' flat bed with tubing sides that come up 5'. The control ***** are still mounted in the cab. None of that stuff is hooked up anymore. Some of those wires could be the problem. We are looking at bad weather for the next few days or more. Once I can I guess I need to get under there and start chasing wires. I was hoping it would come to that. By the way, the truck was custom built as a fleet truck for Good Year. Tommy lift to pick up tires and high tubing walls to keep them in there. Perfect truck for hauling. Thanks for the help.

 

Up Date: I was finally able to mess with this truck some more today. Found the problem. The Left rear tail light was just wired wrong. I have had this truck since 2008. (Which by the way is around the time when I joined this page. Not 2022. Don't know why it's saying that) I remember messing with the wires back then when I fixed it up to pull a trailer. Guess the only question now is 'how did it work OK all this time?' Guess I'll never know the answer to that. Anyway, I appreciate everybody help on this one. Thanks