Never had this happen before

[Breadfather]

Just bought a 77K10 with a sb 400 and a TH 350, when I step on the brakes the front marker lights come on as well as the rear brake lights.  the running lights work when the head lights are on.  when I use the turn signal nothing happens.  No sound from a flasher, nothing.  the thing that is really confusing me is the fact that the front marker lights come on when I hit the brakes.  Is this a crossed wire somewhere?  If so where would be the most common area to check?

any ideas?

[bd]

How many flashers are plugged into the fuse box?  Make sure the hazard switch isn't on.

[Irish_Alley]

also a bad ground or connection can/will cause these problems

[Breadfather]

Sorry it has taken me son long to get back on here.

There is one flasher plugged in at the bottom of the fuse block.

Is there a certain thing I should be looking for when it comes to a bad ground?  Or just loose wires all over the truck?

[bd]

Do this first...

There should be two (2) flashers in the fuse block - one at the top and one at the bottom.  One is for the turn signals, the other is for the "4-way hazard" flashers.  Since your turn signals don't work, replace both flashers and cancel the 'hazard' lights by pulling out on the small stub switch located on the right side of the steering column, near the ignition key cylinder.

I think your brake lights are backfeeding to the front turn lamps, because the hazard switch is pushed in (and the flasher is missing).

Let us know how it goes.

[Breadfather]

well I did not have a chance to buy the new flashers yet, but I pulled out the Hazard switch and tried the turn signals. The passenger sides work while the drive side only lights up the front marker light.

So let me get this straight, IN is ON for the Hazards?  I thought it was the other way around?

From what you have told me, and what is going on now, it sounds like 2 new flashers and the hazard switch out will fix the issue.....I will let you know once the new flashers are in.  One more dumb question.  Is each flasher a separate part number or can i just buy 2 of the same flasher?

man i feel dumb now.

[bd]

So let me get this straight, IN is ON for the Hazards?  I thought it was the other way around?

It's been awhile!      That's how the newer models are.  Your 77 maybe opposite.  I'm confident you'll figure it out.

Both flashers are the same part number.  If you'll be towing, consider electronic flashers; they're constructed differently and will handle the extra electrical load of trailer lights more effectively than thermal flashers.  Once you replace the flashers there maybe more to sort out, but... one bridge at a time.

And, don't feel dumb... how do you suppose I guessed it?   

[rich weyand]

This is the sort of problem one gets when the ground straps on the engine are not re-installed after engine work.  The cab is electrically isolated from the frame by the rubber shock mounts, and so the only ground reference for the cab is the strap from the cab to the engine and then through the strap from the engine to the frame.

There should be one strap from the back of the passenger side head to the firewall.  The engine side of this could be bolted to the outer rear valve cover bolt or to the accessory bolt hole on the head.  The firewall side bolts to the firewall on the flat part of the firewall right next to the curve of the recess for engine clearance.

The other ground strap goes from the accessory bolt hole on the drivers side head (usually the power steering pump bracket is mounted there as well) to the frame rail about even with the back of the steering box.

These are both copper braids with an eye swaged onto each end.

Without these, when you supply power to one system, it tries to find a ground through a second system, and you end up with a lot of "This goes on when this other thing goes on" kinds of faults.

[Breadfather]

I know that loose ground straps can cause all kinds of problems....however in this particular case after much worrying and over thinking, bd comes through in the clutch and called it.  Missing flasher and the hazard switch out plus a burned out rear turn signal bulb.


All said and done...$11 to rock auto and boom its all good.

thanks again everyone!

[rich weyand]

Wow.  Multiple faults are hard to diagnose.  You keep trying to think of what could possibly cause everything you're seeing.

Glad you got it sorted.  Congrats!  That's a tough one.

[Irish_Alley]

burnt running/brake light i guess, if the filament breaks and shorts out on the other. but also a bad connection in the bulb socket will cause this problem, was the socket dirty?

[bd]

Wow.  Multiple faults are hard to diagnose.  You keep trying to think of what could possibly cause everything you're seeing.

burnt running/brake light i guess, if the filament breaks and shorts out on the other. but also a bad connection in the bulb socket will cause this problem, was the socket dirty?

It resulted strictly from how the emergency flasher switch is wired into the system.  The front lamps connect to the rear lamps through the 4-way switch when the e-flashers are turned ON.  The missing '4-way' flasher masked the fact that the 4-ways were switched ON (rear lamps connected to front lamps).  So, the brake lights backfed the front lamps through the switch.  The bad rear bulb was incidental.

[Irish_Alley]

Ahh i see.  Always thought with out a flasher in place it would break the circut of the 4 ways. So the missing flasher was the 4 ways. What stopped the turn signals from working, thought with a bad flasher it would just stay on

[bd]

Ahh i see.  Always thought with out a flasher in place it would break the circuit of the 4 ways. So the missing flasher was the 4 ways. What stopped the turn signals from working, thought with a bad flasher it would just stay on

Flashers can fail open, they can fail closed, and they can fail by a change in flash rate (too fast or too slow). 

In the 4-way flasher circuits used in our square body trucks, the e-flasher is on the battery side of the hazard switch and connected in series with the switch.  The hazard switch completes the series circuit between the e-flasher and the front and rear lamps as it simultaneously connects the front and rear bulbs in parallel.  As a result, all four corners become powered through the one e-flasher and flash in unison. 

On vehicles that share brake and rear turn signal functions using the same lamp, the brake filament and turn/hazard filament are one in the same.  So, when brake lights are energized while the 4-way flashers are turned ON, the power supplied to the brake lights is also supplied to the front lamps through the 4-way switch.  All four corners illuminate constantly until the brakes are released.  This phenomenon occurs whether or not the e-flasher is plugged into its socket. 

You can test this concept by turning your 4-way flashers ON, then stepping on the brakes.  You'll observe the front lamps illuminate along with the brake lights.  At the same time the hazards will stop flashing until you release the brakes.  Now, remove the e-flasher and repeat the experiment.  The front lamps will still illuminate with brake light activation.

In Breadfather's case, the e-flasher was missing and the turn flasher was faulty.  Hence, the turn signals wouldn't flash, the hazard lights couldn't flash, and the brake lights fed the forward lamps, because the hazard switch was turned ON, connecting the forward lamps to the rears.