right turn signal position flashing both left and right turn signals at taillights

[AnarchyAl]

Having a pretty frustrating time with the signal lights. I really could use some help.

It seemed like it should be an easy fix but, after about 15 hours of fighting with it I'm still no further ahead.

 

problem is: when the right turn signal is activated both right signals flash front and back as normal but, the left turn signal also flashes at the tail light. However, when the left turn signal is activated ONLY the left turn flashes front and back.

 

When the brake switch is activated while right turn is selected both left and right flashing lights at tail stop flashing and remain illuminated until pedal is released/ switch opened and the flashing on both right and left tail lights continues

 

Searching this site and many others i have found many helpful suggestions and i have already done the following:

 

changed the multi function switch in the steering column,

replaced all 4 2057 bulbs in tail light housing,

cleaned sockets to remove corrosion and cleaned corrosion from inside socket assemblies wit wire brush/brake clean to make sure there is no short between the metal contact plates.

removed entire rear lighting harness to inspect for chafing/damages and physically seperated all wires for testing. 

removed after market trailer wiring harness

refreshed ground behind drivers tail light

checked all 2057 bulb bodies for continuity to refreshed ground

cleaned and inspected harness connector in cab at drivers side beside hood release 

seperated fuse panel halves to inspect for obvious burned/ chafed wires/ bridged terminals

 

With the right turn selected, using a digital multimeter, i continue to find voltage cycling from 0v-12v-0v present in the grey/blk wire (left turn) in the forward most connector beside hood release lever - with it disconnected from the tail light harness. And also continuity between the grey/blk (left) and the brown wire (right) at this connector with it unattached from tail light harness.  I take this to indicate that the fault lies upstream of this connection. 

 

What am i missing here?? 

Where do i look next??

Any advice or info would be greatly appreciated!! 

 

also: Any tips for reinstalling the two halves of the fuse panel at the firewall? it came apart so easily, why is it near to impossible to put it back together?

 

Thankyou,

Al

 

-1988 jeep comanche 4.0 

 

 

 

 

 

 

[eaglescout526]

So the rears are flashing when you turn on the right signal? But left behaves normally? Part of me would think that the hazard wiring would be interfering. However I’d suspect the left would do the same. 
 

You replaced the turn signal switch inside the column and not the stalk right? Sometimes that gets confused. 
 

Have you refreshed all the grounds and did you inspect the fronts by chance during your cleaning and replacing of the bulbs? 

19 minutes ago, AnarchyAl said:

Any tips for reinstalling the two halves of the fuse panel at the firewall? it came apart so easily, why is it near to impossible to put it back together?

You need another hand with this one. I learned that one the same exact way. As long as someone puts pressure on the other side you’ll be able to get it back together. 

[hgeranium]

I may be completely off base but have you tried replacing the flasher? I had an issue where my brake lights in the back would work, but when I used my right turn signal, the right taillight suddenly turned off and wouldn’t flash nor show the brake lights. Turning on my hazards also made all 4 lights work somehow. I replaced the flasher out of desperation before I chased all the wiring and it solved my problem. Worth a try for ~$10

[AnarchyAl]

Thankyou both very much for the replies!

 

EagleScout, I reused the original stalk, that is correct. I did change the signal light/ multi switch in steering column, yes. and the problem went unchanged. It appears that the stalk is still moving the switch assembly as it should.. I'll look closer at it and check for continuity between circuits with wiring connector at steering column detached.

 

The front signals seem to operate as normal but, considering the voltage is present in left turn signal wiring for the tail light with the connector detached I will go ahead and remove/ inspect/ clean the bulbs up front, as well. Could it be that the front right signal is grounding through the rear left?

 

Two sets of hands?? Now that makes sense. Alone it was driving me batty! I'll get help

 

 

 

Hgeranium, I did try swapping the hazard and signal flasher units back and forth at the fuse panel without any change. 

the wiring diagram leads me to believe that + comes through the flasher to the multi switch and then on to the signals?

 

If it worked in your case, I'll give it a shot!! I'll definitely pick one up today and try it. You're right! for a few bucks it couldn't hurt! I'd be stoked if it works that easily!

 

 

Thanks again guys! Glad to have your help I'll report back after more sleuthing,

 

Al

[Pete M]

the tab inside one of my taillight sockets was crushed flat and not contacting the bulb which caused weird issues.   also do make sure that you check each socket for continuity in case there's a break inside. 

[AnarchyAl]

thanks Pete M! I'll run through them again and check between the contacts individually. I did wire brush/ emery paper the assemblies carefully to remove oxidation that may have been bridging them but, in honesty, i did not check them independently for shorting in the bulb sockets afterwards. I'll get on it!

 

-Al

 

 

[Ωhm]

Not sure here but try this.

 

KEY OFF

With brake switch ON (depressed), can you, using the TS switch, turn OFF the Right Taillight? Same for the Left Taillight, can you turn it OFF using the TS switch? Each one separately.

[AnarchyAl]

Thanks for pointing me in the right direction!

On 11/2/2025 at 7:54 AM, Ωhm said:

Not sure here but try this.

 

KEY OFF

With brake switch ON (depressed), can you, using the TS switch, turn OFF the Right Taillight? Same for the Left Taillight, can you turn it OFF using the TS switch? Each one separately.

 

key off, brake switch on:

 

left turn signal shut off left brake light

right turn signal illuminated front right turn and rear right/left and after a brief moment the flasher relay began to slowly flash all three

 

Disconnected the brake switch and tried the signals again. Right turn flashed without left rear.

 

looking at the brake light switch up close, I discovered that the p.o. had taped in a wire from the brake light switch circuit that followed the multiswitch wiring over to the main harness on the driver's side where it attached to one side of a piece of brown speaker wire!!  it disappears under the trim but somehow it must be crossing paths with one of the lighting circuits and allowing brake + to flow back through to the flasher relay. Disconnected that and now everything works great

 

Had the truck 8 years and it's only been an issue in the last two weeks. Out of curiosity, i'm going to pull the trim and chase the wire until i find the answer.

 

 

Thanks again for suggesting i experiment with that,. It is fixed!

 

-Al

[AnarchyAl]

OH yeah! Turns out you CAN reassemble the fuse panel by yourself: 

 

Install the two screws of the inner cab half of the fuse panel only finger tight. This will give you the resistance to push the two piece harness connector against but also the play you need in order to wiggle them into place. Next, tighten the in cab screws. Then use the center bolt in the connector to draw it it together