Turn signal lights acting weird

[78K204x4]

I did a running light inspection on my 78K20 last week. All was good, till I checked the turn signal lights. The rear turn signal lights are good. When I walked around the front, the turn signal lights were acting like 4-way flashers!
Does that with both left & right turn signal's. I'm at a loss. A few months ago all was fine.
Anyone here ever have this issue ?

[old Rusty C10]

make sure you have the proper bulbs in all your sockets..if they are wrong, it will cause an issue

[78K204x4]

Haven't had to change any bulbs in quite a while.

[Southcity]

Double check all the related grounds. Clean them, secure them, ensure wiring is sound etc. It's easy to do and is a good place to start. Once all that checks out, if you have spare bulbs switch them out one at a time to see if perhaps it's one of the existing bulbs that is going bad.

[78K204x4]

I just went out to the truck & pulled the bulbs out of my western plow lights. Each side has 2 - 1157 bulbs for park & turn lights, plus the halogen headlight bulbs.
I removed all 4 of the 1157's. Checked them over, and re-installed them.
I don't know what happened, but all is good now.
Maybe I had one or more bulb installed wrong.
I hope this isn't one of those intermittent electrical problems.
Seems to be good now.
Thank you, everyone, for your help !

[78K20]

It came back. So it’s intermittent after all.
I guess I’ll start with checking the grounds, and connections.

[Gregski]

Originally Posted by old Rusty C10

make sure you have the proper bulbs in all your sockets..if they are wrong, it will cause an issue

+1

took me like 5 years to figure this out on my truck, GM likes to run the ground through some of the side markers, so if you use the wrong bulb it will make the lights wonkey

experiment with different bulbs until you find the ones that work properly, and then document that

I think I did I write up on this in my Restoring Rusty thread somewhere towards the end

[hatzie]

Think about what you disturbed by checking the bulbs and follow the problem.

I usually grit my teeth when I get a plow or trailer truck in the dooryard with lighting issues.
Plow and trailer wiring, both the truck side and the trailer/plow, usually has some pretty rough workmanship. I've seen some really nasty butchery.
I've ripped out and replaced whole trailer light/brake harnesses. I use the proper gauge wires and decent weatherproof splices and connectors. Plow lights too. Less time and blood pressure raising anger in the long run to roll my own.

[hatzie]

The 168 peanut bulb front side marker lamps do not have a ground on the same leg all the time so you cannot use LED bulbs in those sockets or the 1157A bulbs in the front turn/parking lamp sockets.
How did GM light the bulbs without a ground? GM ran the front side marker lamps from the parking lamp HOT to the Turn signal HOT wires.

This means the 168 peanut bulb side marker lamps on the squarebodies ground through the tungsten turn or parking lamp filament of the 1157A bulbs in the front turn/parking lamp housing. There are a bunch of vehicles made from the 1930's through the 1990's that did this.

When the parking lamps are switched on, the side marker lamps receive a ground through the turn signal filament when the turn signal is off so they shut off when the turn signal is powered on. This makes them light up when the turn signals are off. Kind of a wig-wag on the front corners at night.

When the parking lamps are switched off, the side markers ground through the parking lamp filament when the turn signal on that corner is hot so they light at the same time as the turn signals.

If you use LED bulbs in the front marker lamps and/or your front turn/parking lamps you'll likely get strange behavior from your front turn and parking lamps.

[78K20]

I believe I’ve narrowed the problem down to my steering column.
I put a tilt column in a while back. Well, the “swivel” part of the
column was extremely loose. Loose enough that it bothered me
for safety. So, I reluctantly took the column apart, to get to the
problem. There’s 4 screws that come loose on these tilt columns.
It takes a lot of time to get it dismantled down to the problem area.
I’m thinking I crossed a couple wires during the process. So now,
I’m thinking about changing out the tilt column for a fixed one.
Hate like hell to loose the tilt, but I need my front directionals!

I hope my screw up will be a lesson for those that are considering fixing
their floppy tilt !
You have to be very careful not to disturb the wiring when doing the repair!
The wiring was extremely tight when I was trying to get the dismantled section
off the steering shaft.
Everything points to the column wiring for the problem.
I’ve removed & cleaned all the grounds, & checked all the bulbs.
No LED bulbs on this truck yet.
I need to start hauling firewood home with this truck, so I guess I’m gonna
have to get after it soon !
I’ll do an update as soon as I get a fix, whatever that will involve.

[fun in dirt]

Originally Posted by hatzie

The 168 peanut bulb front side marker lamps do not have a ground on the same leg all the time so you cannot use LED bulbs in those sockets or the 1157A bulbs in the front turn/parking lamp sockets.
How did GM light the bulbs without a ground? GM ran the front side marker lamps from the parking lamp HOT to the Turn signal HOT wires.

This means the 168 peanut bulb side marker lamps on the squarebodies ground through the tungsten turn or parking lamp filament of the 1157A bulbs in the front turn/parking lamp housing. There are a bunch of vehicles made from the 1930's through the 1990's that did this.

When the parking lamps are switched on, the side marker lamps receive a ground through the turn signal filament when the turn signal is off so they shut off when the turn signal is powered on. This makes them light up when the turn signals are off. Kind of a wig-wag on the front corners at night.

When the parking lamps are switched off, the side markers ground through the parking lamp filament when the turn signal on that corner is hot so they light at the same time as the turn signals.

If you use LED bulbs in the front marker lamps and/or your front turn/parking lamps you'll likely get strange behavior from your front turn and parking lamps.

I have been looking at wiring diagrams for 2 days, before seeing this post, trying to understand this layout - Thanks for this explanation!!!

[mMad Dawg]

I have had the same thing happen to me. Turns out it was one of the elements in the broke loose and made contact with the other element . Take the bulbs out and flick the glass with your finger. Watch the elements you will see the bad one move. Hope this helps.

[Gregski]

thanks for letting us know, and this is not the first time I heard tilt column whoas

[Southcity]

^agreed^ - thanks for letting us know and providing the update. Even though dealing with your tilt column is a bit frustrating, there is some satisfaction in having potentially found the issue yourself so....good job!

[hatzie]

The turnsignal harness isn't that bad to pull into the column. It looks a whole lot more daunting than it is.

The one thing you have to be sure about is the location of the plastic guide/tray (#9 in the blowup).

According to the parts books the 1978-1983 turn signal switch 1997985 is the same for tilt and non tilt columns. Amazon has the AC Delco Professional 1997985 switch for $27.
https://www.amazon.com/ACDelco-19979.../dp/B000C9EL9U

Parts blowups for 1979-83, 1978 is the same.

[78K20]

Thought I’d post an update.
It’s not a good one. I’ve removed every bulb, inspected, replaced any that may be faulty. I’ve removed every ground that I can find, cleaned, sanded, installed new star washers, etc. I bought a new ACDelco turn signal switch ($50). And yes, I put the plastic tray back in it’s correct position. I have a non tilt column to use as a reference.
I thought I had the problem fixed a couple days ago. I worked on the truck ALL day. When I got done, the turn signals were working as they should. So, I got a cold bottle of Modelo & watched the turn signal action for quite a while. Going from left to right, back & forth, for a long time. Why I was almost giddy !
So................
The next morning, I went out to the truck to replace a couple ty-rod’s (Moog $181.00) and couldn’t help myself from checking the turn signal action again.
Went right back to 4 way flasher mode!
I was seriously considering getting my 45 !
Oh, and I also replaced the flasher.
This problem is intermittent. It happens while I’m standing in front of the truck, not even touching anything.
And it’s weird, it’ll go complete 4 way mode, or sometimes it’ll just give a slight blink just to let me know it’s still there.
Doesn’t matter which side of directional I have on, it goes bonkers on both.
I think I need to give my guns to someone for safe keeping ( for the trucks) until this issue is put to rest.

[hatzie]

You have plow lights. I assume you also have a trailer plug.

Both of those add on lighting systems tend to add all kinds of fun to the equation from installation mistakes and poor workmanship.
Vehicles this old were usually worked over by 16-20 year olds working for U-haul or Ryder or some other hitch dealer out back and Western, Fisher, Meyer, or some other plow dealer up front. I've seen some pretty rough looking workmanship with Scotchlocks and open butt splices to both lighting harnesses not to mention the mess where the main power for the plow is tied in.
I explain to the customer what exactly they're up against and where this could go.
When they say fix it I go to work to clean things up while wishing a swarm of fleas and ticks could infest the undergarments of the damn kid that created my latest cleanup job.
If they beg off I heave a sigh of relief.

When I work this kind of nasty miserable intermittent I try to split things up to narrow down where the fault lies.

1978 Gm Light Trucks are a pretty simple lighting setup.

At the firewall bulkhead disconnect GM engineers thoughtfully segregated the forward and rear lighting are in two separate plugs. These two plugs are even separated from everything else.

You can unplug the front and rear lamp plugs from the bulkhead and reinstall the everything else plug so the cab, engine, etc still get power.
If the flashers work LH, RH, 4-way each in the proper manner with the front and rear lighting plugs removed from the bulkhead then the fault lies after the bulkhead plug.
Plug one of the lamp harness plugs back into the bulkhead plug then plug in the other. With any luck one of them will be infested with the bug you're chasing.

My guess is that your problem is in the Fisher, Western, Meyer, or some other forward lamp wiring rats nest. Not that yours is a rats nest but you would be the extreme exception in this case.

[gafiredog]

I have the same problem with my turn signals. I have a 87 dually with a tilt, it too was all messed up, and instead of repairing it in the truck, i took it out, and plan to do a complete rebuild. but in the mean time, I replaces it with a fixed unit I had lying around, after installing it, all the lights work but no turn signals, I can;t find the problem anywhere, however, there was a trailer brake box that the po had put in, and i did not use it, it was all wired up, with wires going everywhere, I just cut the wires going into the box, not thinking they may cause problems with the other wiring... any ideas????

[78K20]

Originally Posted by hatzie

You have plow lights. I assume you also have a trailer plug.

Both of those add on lighting systems tend to add all kinds of fun to the equation from installation mistakes and poor workmanship.
Vehicles this old were usually worked over by 16-20 year olds working for U-haul or Ryder or some other hitch dealer out back and Western, Fisher, Meyer, or some other plow dealer up front. I've seen some pretty rough looking workmanship with Scotchlocks and open butt splices to both lighting harnesses not to mention the mess where the main power for the plow is tied in.
I explain to the customer what exactly they're up against and where this could go.
When they say fix it I go to work to clean things up while wishing a swarm of fleas and ticks could infest the undergarments of the damn kid that created my latest cleanup job.
If they beg off I heave a sigh of relief.

When I work this kind of nasty miserable intermittent I try to split things up to narrow down where the fault lies.

1978 Gm Light Trucks are a pretty simple lighting setup.

At the firewall bulkhead disconnect GM engineers thoughtfully segregated the forward and rear lighting are in two separate plugs. These two plugs are even separated from everything else.

You can unplug the front and rear lamp plugs from the bulkhead and reinstall the everything else plug so the cab, engine, etc still get power.
If the flashers work LH, RH, 4-way each in the proper manner with the front and rear lighting plugs removed from the bulkhead then the fault lies after the bulkhead plug.
Plug one of the lamp harness plugs back into the bulkhead plug then plug in the other. With any luck one of them will be infested with the bug you're chasing.

My guess is that your problem is in the Fisher, Western, Meyer, or some other forward lamp wiring rats nest. Not that yours is a rats nest but you would be the extreme exception in this case.

It must have been a bad connection somewhere in the front wiring harness.
I don’t know where exactly, but I took apart several connections & cleaned
them up & put them back together.
I’ve checked the function several times over the last two days, & it’s working as it should. I don’t trust it yet, so I’ll have to keep an eye on it when I start driving it again. While I was under the truck yesterday, I noticed my water pump leaking, so I’m waiting for that to show up from Rock Auto.

I want to thank you, for your help / advice. It’s greatly appreciated!