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Ok, so I had every turn signal and driving light working except the front drivers TS, which would only blink if the driving lights were off. If the driving lights are off, it will now cause the two small side marjers lights to blink when I turn on the switch. At the same time, my rear passenger yurn signal no longer works! It worked fine until I unplugged that front drivers side 4 prong plug. Conversely, the rear drivers side turn signal works fine with the front plug unplugged or plugged in. So, I believe the front 2 hole, 2 prong plug could be grounded inside the plug itself. Does this sound like a reasonable deduction?

Brake lights work both sides
Backup lights work both sides
Tailights work both sides
All driving lights work
Front Turn signal causes the two drivers side side markers lights to blink now.
Rear passenger turn signal stopped working when I played with Drivers side 4 prong harness connector.
With front harness unplugged, rear drivers turn signal does not cause side marker to blink, only when the front harness is plugged in

Headlight connector is not connected as I have made a different harness for those already.

Should I cut the 4 prong connector and hard wire it to see if it is the connector itself? Or is the turn signal switch going bad?

1978 Bronco.

Thanks!
 

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In my experience with my '78, it always turned out to be a ground issue. Usually a bad ground inside a light socket (the 4 "big sockets" at the corners). The ground prong that touches the bulb inside the socket usually corrodes inside the socket where it connects to the ground wire itself. May look ok, but won't function correctly. I've pulled many handfuls of hair out trying to diagnose it.....

Check ALL of the lighting grounds, and grounds from the body/ motor/ frame. Each headlight has a ground to the core support that gets easily corroded & breaks contact.

Did I mention checking the grounds???:histerica

Bad grounds can cause tons of weird stuff to happen, especially on newer rigs.......:banghead
 

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Discussion Starter #3 (Edited)
In my experience with my '78, it always turned out to be a ground issue. Usually a bad ground inside a light socket (the 4 "big sockets" at the corners). The ground prong that touches the bulb inside the socket usually corrodes inside the socket where it connects to the ground wire itself. May look ok, but won't function correctly. I've pulled many handfuls of hair out trying to diagnose it.....

Check ALL of the lighting grounds, and grounds from the body/ motor/ frame. Each headlight has a ground to the core support that gets easily corroded & breaks contact.

Did I mention checking the grounds???:histerica

Bad grounds can cause tons of weird stuff to happen, especially on newer rigs.......:banghead
Now that I think about it, it is probably the front turn signal socket. I bet it is grounded inside the socket bleeding through to the marker lights, causing them to blink. Then when I turn on the running lights, that direct voltage overpowers the weak bleed through voltage and cause the strait lighting with no blinker break-up.

Ok, checked the 4 connector plug going to the lights for the marker and signal, found the brown wire which is "power", grounded. This certainly narrows it down to the wires or socket itself, I'm guessing socket as you stated earlier.
 

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I ran into a somewhat similar problem in my 79. None of the turn signals were working, the lights would intermittingly turn on and off while driving, and sometimes while I had them on and parked. I traced most of it to a bad headlight switch, and some jacked wiring from the PO. Getting it wired up right the blinkers now make all the turn lights blink, I'm thinking the grounds and connectors could be an issue too. Not had much time to look into it lately but hoping this weekend I'll get a lot accomplished.

Let us know what you end up finding.
 

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I'm having problem with my turn signals as well. The hazards work, even light both arrows up on the dash. My passenger side front or my drivers side back do'nt work. My drivers arrow light up on the dash with the turn signals, but the passenger side does not.
 

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You too have a grond issue. Fix that and your signals will work. There is not a problem with your dash lights. They reflect what the rear lights are doing: So, if you have no rear t/s, you will not have an arrow on that side.

SWS
 

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Discussion Starter #7
UPDATE:

Al lights are working! Turned out to be the turn signal switch, which was changed when I put in the different steering column. Front turn signal works properly, and the rear signal turned out to be a bad socket, even though it was new. Cheap china, blah. Anyhow, the combination of the signal switch (with working cams now) and sockets turned out to be the culprit.
 

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Will say to drunk & didnt read all of the posts....

I had MAJOR blinker probs... What it came down to was the bulbs were in wrong... Sounds stupid & all that but that is what it was..

I did the whole ground thing mad new for every light,added a few extra from body to frame.. All it was was the bulbs at all 4 corners were not sitting just right
 

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Anyone have any suggestions on my turn signal issues? Have a 78 Bronco with a 400. turn signals were working fine, then all the sudden the other night nothing! I checked the fuse and it was blown so I replaced it. Replaced the flasher as well. Anytime I have the headlights on and use the left signal now it blows the fuse and left with no signals. Any ideas? Also before it blows the fuse when i flip the signal on to the left, the dash and headlights dim.... Please help!
 

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Discussion Starter #12
Anyone have any suggestions on my turn signal issues? Have a 78 Bronco with a 400. turn signals were working fine, then all the sudden the other night nothing! I checked the fuse and it was blown so I replaced it. Replaced the flasher as well. Anytime I have the headlights on and use the left signal now it blows the fuse and left with no signals. Any ideas? Also before it blows the fuse when i flip the signal on to the left, the dash and headlights dim.... Please help!
Go to the front wiring harness that plugs the headlight, turnsignal, and sidemarker light. It should be a black 4 connector plug. Un-plug it, and and see if your back light and signals work without blowing the fuse. You have a direct short, isolte front and back to send you in the right direction, or send you towards a switch.

Also, get a good meter and check grounds...maily on wires that SHOULDN'T be grounded...
 

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I had this same issue. I had to jump a wire around the bulb fixture. Somehow it shorts out internally. I just used a multimeter and checked for continuity where there shouldn't be any. Snipped the offender and jumped it to the little metal plug that sticks out the front by the bulb.....Your situation may be different, but these things seem to fail sometimes.
 

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I have a similar issue. When the headlights are off, my turn signals work fine. When I have the running or headlights on, the left turn signal indicator stays on constantly. It will not flash when pressed either. Does this sound like what was discussed in post #3? If not, where should I start? Also, where is a good place to get parts I may need to resolve this? I just picked up my Bronco and would like to get it squared away.
 

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I have a similar issue. When the headlights are off, my turn signals work fine. When I have the running or headlights on, the left turn signal indicator stays on constantly. It will not flash when pressed either. Does this sound like what was discussed in post #3? If not, where should I start? Also, where is a good place to get parts I may need to resolve this? I just picked up my Bronco and would like to get it squared away.
bad ground at the socket sounds like .and is feeding back through blinker filament to get ground

easy to detect which one
pull a bulb on side not working,turn on parking lights and see if turn indicator is lit
my front ones were the issue
could be just a bad bulb too
had that happen before,the filament breaks off and welds across both terminals inside the bulb
 

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bad ground at the socket sounds like .and is feeding back through blinker filament to get ground

easy to detect which one
pull a bulb on side not working,turn on parking lights and see if turn indicator is lit
my front ones were the issue
could be just a bad bulb too
had that happen before,the filament breaks off and welds across both terminals inside the bulb
Great, thank you,I will try that and report back. I'm out of town for a few days, but will check as soon as I'm back.

Would an O'Reilly's or similar auto parts store have the socket of I have to replace the whole unit?
 

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Now that I had a chance to get to my truck, I found out a few things.

The constant on turn indicator seems to have gone away for now.

The front passenger side turn signal will not blink when the headlights are on, but blinks fine when the headlights are off.

All four small corner marker lights will not work. They look corroded from mud. New bulbs didn't work. Should I cut out the old sockets and replace with new ones? Would an autocrats store have the correct size, or should I go directly to an online source?

Thanks!
 

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I'd go ahead and clean the sockets up first. Use a small nail file or piece of sand paper. Check your grounds first like rusty said. Do you have a good test light? As for the parts, all should be found in the parts store. Just be careful of quality in them.
 

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I'd go ahead and clean the sockets up first. Use a small nail file or piece of sand paper. Check your grounds first like rusty said. Do you have a good test light? As for the parts, all should be found in the parts store. Just be careful of quality in them.
It should be a good light, it came out of my car when I replaced them with LED's.
 
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