Odd problem. Maybe you all can help... 1986 in the profile picture.

So, I have begun changing out all my bulbs for LED, I started with the headlights and harness mod. THen I did the front bumper turns (rectangles) and the tail turns and tail brakes. I have the second tail brake in the mail as well as the corner ambers up front (194s)

This is when I realized my voltage was apparently not reading correctly now so my High Beam indicator was extremely dim, if on at all. So, I pulled the cluster and decided to change the two white 194s for the main gauges, the two turn indicators and the blue headlight high beam indicator. I did so with 194s from SuperBrightLED.

This is where the funky issue comes in. Now, whenever I hit my brakes both my turn indicators illuminate at half bright (not full bright as if I actually hit the turn signal) and stay illuminated until I release brake. So...now I have in cab brake light indicators in the form of two arrows. Brake lights still work on the exterior as well... Also, I don't remember if this is normal, but brakes also illuminate when key not engaged and in total off position (but I think that's normal...).

I can live with this, if I need to. It's not a huge deal, but if it's easily fixable, great. I'm guessing it has to do with a lack of resistance that is loading the circuit and jumping to the turn indicators.

Important to note ONLY the indicators on the instrument cluster trigger, NOT the actual turn signals on the exterior of the truck. THAT would just be silly...

Anyone have any thoughts or suggestions?

Thanks ahead of time.

 

This is usually a bad ground at the taillight housing, causing backfeed to the turn signal lamps. The housing grounds to the body thru the mounting studs. There should be a removable panel inside the bed for each housing, that can be removed to get to the studs & nuts holding the housing onto the bed. Over time rust & corrosion can develop at the studs and cause a bad ground connection, due to the gaskets for those covers rotting away & letting water in there. It's easy enough to get in there, remove the nuts & clean the surrounding area back to bare metal, then reinstall the nuts.

I have no sources for the gaskets, so I just ran some silicone RTV around the covers & reinstalled them.

 

Yea, I was thinking that, but the turns themselves don't flash or light, only the dash cluster indicators for the turns. It also only happened after I installed the instrument cluster LEDs. Would it still be the brake lights triggering the feedback into the instrument cluster? I'll check the grounds today, I'm going to replace those tail 194s with LEDs being delivered.

If the brake lights are causing the feedback to the instrument cluster leds, would I be able to just jump some resistors into the in on of the tail light bulbs to suck of that juice?

 

Had the same issue when changing all my dash lights to LEDs. Besides the turn signal indicators, one or two of the warning lights were staying half lit from voltage backflow. Instead of messing with resistors or diodes, I just put regular bulbs back into the dash cluster where I had issues.

 

Yea, I may do that. I like the nice, bright turn arrows, but I keep glancing because my brain triggers as 'turn signal still on' when i tap my brakes.

 

I never liked the idea of resistors to cut down on voltage. Diodes may work only allowing flow one way?

 

I totally agree on the resistors. Having something that is just absorbing juice and expelling heat while technically shorting connections as a rig solution gives me bad dreams.

 

Did you get the "no polarity" 194 bulbs, like these: ? If so, my money is on a poor ground in the rear combination lamp.

With just a small resistance to ground, the brake lamp bulbs pull enough current to raise the ground-side of the combination lamp a few volts. The brake bulbs are as bright as ever; they have an internal resistor to limit current but 9-10 volts is plenty to light them. The raised voltage on the ground side of the turn signal bulb back-feeds through the bulb ("no polarity") to the turn signal indicator. The turn signal indicator lights while the turn signal bulbs don't because the indicator is a tiny lamp that needs little current to light.

On my '94, the bed is insulated from the frame (noise isolation), so attaching a ground to the sheet metal is a waste of time. The factory wiring includes a ground wire. If your wire (or body connection?) has only a few ohms from the bulb socket back to the ground in the combination meter, that will be plenty. As a test, hook up a long piece of 18ga (or bigger) wire to the battery ground. One of your 194 bulbs connected between that wire and the ground side of the combination lamp will probably light when the brake lights are on.

You can probably fix it by replacing (or installing) the ground wire from the combination lamp back to the harness, as long as the combination lamp sockets are okay. Or get "regular" polarized LEDS for the brake lamps.

Resistors won't do anything for you here. Their purpose with LEDs is not to drop voltage, it's to increase current draw (back up to where it was with the old incandescents) to trick the turn signal relay (or dimmers, etc.) to run at the correct rate.

 

Hmmm. Ground are ok. Can't find polarity-sensitive bulbs that bright enough. You think installing diodes on the positices for the brake lamps would do the trick?

If so, what should the rating be, a couple amps just in case? These lights I have now pull .27 amps at max.

 

Figured it out.

PO had installed a janky u-haul trailer harness with scotch locks behind the lamps. I chopped the hots going from the brake harness to the trailer harness and everything stopped feeding back. That means it's been doing this for years, I just now noticed it because of the lower power LEDs allowing the feedback to matter.

Pulled the harness out completely, removed scotch locks, repaired wires.

Problem solved.

Thanks everyone.