Unbelievable Turn Signal Issues

[atvjoey]

Hello,

This is my first post so bare with me if its in the wrong spot. I just bought a 1987 gmc r15 and I knew it had problems but these turn signals have me stumped. Someone before me replaced the turn signals with some kind of motorcycle light I think or maybe trailer lights and when I engage the left turn signal the front turn signals both flash and both rear sides flash (just like turning on hazards). Now for the crazy part, if I turn on the right side turn signal, none of the lights blink but the flasher engages and the fuel pump on the driver side fuel tank turns on. Its not a priming its as long as the turn signal is on the fuel pump runs. Does anyone know where to start looking? I have been doing simple things like flasher can, fuses, replacing bulbs for the light problem but I do not know where to start with the fuel pump problem. Any help would be much appreciated.

-Joe

 

[dsteelejr]

Not sure what you mean by motorcycle light or trailer light. Any pics?

Start by getting yourself a wiring diagram for your truck if you don’t already have one. You can download one from the reference library on this forum.

https://www.gmsquarebody.com/threads/1973-1991-wiring-manuals.14498/

 

[Bextreme04]

I've seen missing grounds cause some cray stuff like this. Internal shorts inside the headlight switch can also cause some crazy stuff like this.

 

[atvjoey]

I can get some pics later tonight up close I don't have any on hand. They are basically very small led lights about the size of my finger. I have been trying to trace relays and such so far with no luck. Under the dash, the wiring looks ok except for a slightly melted hazard flasher can slot so I am thinking its got to be somewhere in the engine bay or underneath the truck.

 

[atvjoey]

I've seen missing grounds cause some cray stuff like this. Internal shorts inside the headlight switch can also cause some crazy stuff like this.

Any grounds in particular that people either don't know about or are easily broken/corroded?

 

[SirRobyn0]

Pictures of the non-factory lights might help.

Looking at diagrams might help. There is a lot of stuff we can help you with on the forums, but some electrical issues, especially such an extreme odd issue such as this one somebody almost has to be there to see it to know what's going on but I've got an idea.

Take a picture of the non-factory lights and up load it to this thread.

What happens when the truck is running? Will it run off of both tanks? When you switch it to the driver side tank does signal start to flash? Does it stop running?

Does the fuel pump run continuously when the signal lever is engaged or does it pulsate?

Ideas I have off the top of my head. Possibly so kind of odd ground issue.

Can you disconnect those aftermarket lights and see if the fronts will operate and / or see if the pump stops coming on with the turn signal lever?

No offence I have no idea what your experience level is, are you sure that the pump is actuating because the turn signal lever is on?

Also if you could take video demonstrating this it would be the next best thing to actually being there.

 

[SirRobyn0]

I can get some pics later tonight up close I don't have any on hand. They are basically very small led lights about the size of my finger. I have been trying to trace relays and such so far with no luck. Under the dash, the wiring looks ok except for a slightly melted hazard flasher can slot so I am thinking its got to be somewhere in the engine bay or underneath the truck.

Start by disconnecting those LED lights. You have no idea how many times I've seen cheap or damaged aftermarket LED lights cause issues. No one exactly like yours, but still would be a good place to start.

 

[atvjoey]

Pictures of the non-factory lights might help.

Looking at diagrams might help. There is a lot of stuff we can help you with on the forums, but some electrical issues, especially such an extreme odd issue such as this one somebody almost has to be there to see it to know what's going on but I've got an idea.

Take a picture of the non-factory lights and up load it to this thread.

What happens when the truck is running? Will it run off of both tanks? When you switch it to the driver side tank does signal start to flash? Does it stop running?

Does the fuel pump run continuously when the signal lever is engaged or does it pulsate?

Ideas I have off the top of my head. Possibly so kind of odd ground issue.

Can you disconnect those aftermarket lights and see if the fronts will operate and / or see if the pump stops coming on with the turn signal lever?

No offence I have no idea what your experience level is, are you sure that the pump is actuating because the turn signal lever is on?

Also if you could take video demonstrating this it would be the next best thing to actually being there.

I will try to upload more pictures tonight and maybe a video if I can. The fuel pump is definitely on as I put my ear right up to the tank and its definitely on. The truck will remain running if the turn signal is on and funny enough the only reason I figured out this problem was I was checking bulbs with the truck off and I heard it. The pump stays on as long as the turn signal is on but it does pulsate slightly with the blinker. The wiring has definitely been hacked up in the engine bay (whenever I see wire nuts I know I'm in for a bad time). I know the gas tank switch works but I don't want to run it on the passenger tank since I think the previous owner let gas sit in the for a few years without using it.

 

[Bextreme04]

Troubleshooting 101.. take your time and be methodical. Step 1 is verify the fault. This means you need to do a function check and write down what works when it should, what doesn't work when it should, and what works when it shouldn't. All of those things will help point you in the right direction to start troubleshooting the issue more specifically. A melted flasher module likely means there was a short to ground or overvoltage condition at some point that caused the connector to overheat.

 

[AuroraGirl]

Hello,

This is my first post so bare with me if its in the wrong spot. I just bought a 1987 gmc r15 and I knew it had problems but these turn signals have me stumped. Someone before me replaced the turn signals with some kind of motorcycle light I think or maybe trailer lights and when I engage the left turn signal the front turn signals both flash and both rear sides flash (just like turning on hazards). Now for the crazy part, if I turn on the right side turn signal, none of the lights blink but the flasher engages and the fuel pump on the driver side fuel tank turns on. Its not a priming its as long as the turn signal is on the fuel pump runs. Does anyone know where to start looking? I have been doing simple things like flasher can, fuses, replacing bulbs for the light problem but I do not know where to start with the fuel pump problem. Any help would be much appreciated.

-Joe

sounds like an interesting short to power related to the ignition switch probably on first gut reaction, but I dont like your title.
I believe the scenario. I believe its possible and that it has happened. 0/10 not enough explosions

 

[AuroraGirl]

I can get some pics later tonight up close I don't have any on hand. They are basically very small led lights about the size of my finger. I have been trying to trace relays and such so far with no luck. Under the dash, the wiring looks ok except for a slightly melted hazard flasher can slot so I am thinking its got to be somewhere in the engine bay or underneath the truck.

well a melted hazzard can terminal means that the hazzard circuit had enough amps or resistance on that pin, such as a turn signal bulb socket drawing too much because shorting to ground, or the resistance at the fuse box was high and that terminal made enough heat to melt the plastic around it and if it was that hot, it maybe melted somethign on the backside or toasted the plastic which holds all the fuse and power circuits from touching eachother and such. I would like a picture of the damage you say. Also that means a review of the harness at the sockets in each place is a good idea, and the ground on the driver side tail light(I think driver... its on one side) to the bed of the truck should be reviewed too. #8 screws holding the light covers and backing piece. The forward lighting should be reviewed at the forward lamps, yes, but the side marker too which is smaller, but the bulb contacts are far closer together than the forward bulb, i think, and could have conductive shorting across from dirt and rust and stuff. that bulb is supposed to flash on a polarity switch with the front turns, so a led would only work as a side marker or a turn, but i dont think both. or may flash at the wrong time compared to a incandescent, i think. the front and rear socket bulbs have sockets that get rusty and people shove the wrong bulbs in all the time.

Then if you have trailer wiring, how was it spliced in? Maybe someone used stupid tap blocks and that was it, and you have a bunch of trailer wires tapped off the tail light harness close together with multiple live circuits with poor crimps allowing exposed wires to dangle and touch things like frames or bumper brackets or eachother or whatever else was mangled with potentially

Then of course, grounds. Ground bus bar by your feet on the cab with grounds on it, maybe rusty. Also hows your column wiring connection look

 

[Ellie Niner]

-Picking these things apart a bit at a time can be helpful. Like SirRobyn0 said, get all of the LED lights out of the circuit first.

Does the right turn signal activate the right fuel pump if the flasher is removed? It probably won't.

Does hazard flasher work, or turn on fuel pump?

Does fuel pump still come on when you have tank selector set to "Left Tank"

You should have less than 10 amps on the hazard circuit with correct bulbs, so that melted spot is troubling...

 

[AuroraGirl]

-Picking these things apart a bit at a time can be helpful. Like SirRobyn0 said, get all of the LED lights out of the circuit first.

Does the right turn signal activate the right fuel pump if the flasher is removed? It probably won't.

Does hazard flasher work, or turn on fuel pump?

Does fuel pump still come on when you have tank selector set to "Left Tank"

You should have less than 10 amps on the hazard circuit with correct bulbs, so that melted spot is troubling...

and those flashers dont get removed much, the pins should have good contact to the block making the resistance idea less likely(meaning a larger load or short of some kind of excess etc

 

[Ellie Niner]

and those flashers dont get removed much, the pins should have good contact to the block making the resistance idea less likely(meaning a larger load or short of some kind of excess etc

10/10 for your deductive reasoning!

Edit: Hey! This thing ate my emoji!!

 

[atvjoey]

Alright I did a bit more diagnosis before I called it a night and I have a few pictures of the lights and hazard flasher can plug attached. If I flip the dual tank switch to any other setting the fuel pump won't engage but it will still blow the turn signal fuse (I think I forgot to mention leaving the right turn signal on will blow the fuse after a bit of time). Also, I found out that the left turn signal doesn't work at all if the headlights are on and that if the headlights are off the left turn signal blinks/flashes the dash lights. I will also add that the fuel pump will always go on no matter the headlights if I turn on the right directional. I have not checked the bus bar I will check that tomorrow. Also, there is no wiring for a trailer on the truck.