Converting to separate, amber turn signals in rear

[Catrik]

Hi,

1986 K10. I'm trying to figure out how to stop brake light from flashing when turn signal is on. I am converting to have amber turn signals in the rear.

Quote from service manual X8632_1986_GMC_Light_Duty_Truck_CK_G_P_10_to_30_Service_Manual.pdf

REAR TURN, STOP, AND
HAZARD SYSTEMS

These three systems use the same bulb in the rear
lamps. When the rear turn system is turned on, a
thermal oscillator is turned on, which causes the
system to flash. The front park lamps are also a part of
the turn system.
The stop lamp system is turned on by a brake switch
closing. The two rear bright lamps are then turned on.
The hazard system is turned on by the hazard
switch. The hazard system thermal oscillator is then
turned on which causes the front park lamps and the
rear bright lamps to flash.

Does thermal oscillator mean relay? How do I isolate the rear turn signals from the flashing circuit?

[Irish_Alley]

they cant. they both use the same filament, the bulb is a dual filament bulb and one uses the turn/brake while the other one is the running light.

[Catrik]

Oops, I meant to say "isolate BRAKE light from the flashing circuit". I will be using front turn signal circuit for the rear turn signals also. So I just need to stop my brake lights from flashing when turn signals are on.

[bd]

Each OEM rear lamp uses a single, dual-filament 1157 bulb.  The rear turn and brake functions share, but independently power, the larger bulb filament using one of the two contacts on the bottom of the bulb.  The taillight independently powers the smaller filament using the remaining contact on the bottom of the bulb.  The opposite ends of both filaments connect together inside the bulb and to the metal casing of the bulb to complete the turn/brake and taillight circuits to ground.  The shared filament of the 1157 bulb restricts the way in which the lamp can be wired to the turn and brake circuits. 

Are you physically replacing the rear lamps with a different style lamp configuration that has separate turn and brake bulbs?  If your answer is "No" then you are stuck with the factory configuration.  If your answer is "Yes" then the brake circuit can be separated out from the turn signal switch to power the brake lamps independently of turn and hazard functions.

[Catrik]

If your answer is "Yes" then the brake circuit can be separated out from the turn signal switch to power the brake lamps independently of turn and hazard functions.

Yes. That's what I am asking, where do I need to cut/modify my wiring so the stock rear lights no longer have turn signal or hazard feature.

[JohnnyPopper]

Is your avatar the truck you're working on? If yes, do you have replacement tail light assemblies that contain a third bulb?

You will have to add at least one more wire from the cab to the tail lights.

I may be wrong, but I see using the existing brake light wires to feed your 'new' turn signal light bulbs.

Use the new wire to feed the brakes in parallel, looping from one assembly to the other.

BD is the source of wiring diagrams.

[bd]

Disconnect the white wire from the brake light switch and tape up the bare end.  Connect a new red wire to the brake switch and run it to the rear of the truck, connecting it as described by JohnnyPopper.

[JohnnyPopper]

You make it sound so easy BD! Thanks, I really thought he might be in for more drama than that.

[bd]

Actually, depending on the hardware you plan to use rewiring might prove trickier at the rear than initially indicated since circuits will need to be split and rerouted to the "appropriate colors" (e.g., do you separate the turn/hazard circuit or the brake circuit from the existing bulb).

[Catrik]

Disconnect the white wire from the brake light switch and tape up the bare end.  Connect a new red wire to the brake switch and run it to the rear of the truck, connecting it as described by JohnnyPopper.

Well, now that you said it, I don't know why I ever thought this was anything complicated at all hah

I'm doing new wiring harness to get a 7 pin trailer socket so I have all the necessary wiring anyway. Thanks for help everyone!

[JohnnyPopper]

Is your avatar the truck you're working on? If yes, do you have replacement tail light assemblies that contain a third bulb?

Any info on this question?

[Catrik]

Is your avatar the truck you're working on? If yes, do you have replacement tail light assemblies that contain a third bulb?

Any info on this question?

Yes, it is. No, I don't. I'm installing turn signals on my bumper. https://www.youtube.com/watch?v=9jV_tmb2j-8 these would be pretty cool but they are 100€. For one.

[JohnnyPopper]

Really?!

Don't they know you need at least two?

What would you do with JUST ONE???!!!???

This one's only 11.00

[roundhouse]

A lot of the turn signal / brake light stuff is handled by the turn signal & flasher switch assembly on the steering column

I’d just remove the existing wires from the break pedal switch and run a new wire feeding the brake light switch on the brake pedal and run it with a new wire back to the stock brake lights

Then move the turn signal wire from the current light to the new amber light

This would remove the turn signal from the brake light circuit totally



You in OZ or UK  or a place that requires amber signals ?

Depending on your local requirements for area size of the signal lenses , there are lots of thin LED lights than could be mounted on top of the bumper

Plenty of motorcycle turn signals etc

[VileZambonie]

Just curious if any of you have ever installed a trailer wiring harness?   Now think about how that works