Small voltage in gauge backlights from right turn signal

[1buckeyefan1]

Alright, hopefully this is an easy question that someone else might have seen before..

I've been wiring up my Dakota Digital RTX gauge.. as been lots of fun as detailed here. I'm down to the end of it and have a curious error when i use my right turn signal of my Flaming River Tilt Steering column: It wants to send ~2 volts to my dimmer light circuit. I have tested this with a multimeter.. full 12v when i turn on my headlights, 0v with my headlights off and a pulsing .5 to 2v when i only turn my turn signal right. nothing from left turn.

The challenge is that i used this circuit to activate the dim (backlight) on my RTX cluster. So any time i turn right now, it flashes like an xmas tree.

I've attached the circuit diagram from my painless harness. I've tested multiple points (ie, radio, gauge cluster, etc) and it's all being fed this pulsing .5 - 2v.

Any ideas where this voltage may be coming from so I can isolate/remove it? My only two thoughts are 1.) cam on the steering column.. but how is it getting into that circuit then? as there isn't any dimmer activation on the steering column. 2.) a bad ground somewhere.. but everything else on my dash is working properly and I've got good grounds on teh steering wheel, firewall, dash, etc 3.) some oddity with my flashers, as i'm also attempting to run LED turn signals. I've converted my flasher modules to painless ones for LED's.

Any ideas on how to isolate & determine where this voltage may be coming from?

 

[Oldtimer]

There is a lamp in turn signal switch (to illuminate the gear selector) that is connected to dimmer circuit.

 

[1buckeyefan1]

There is a lamp in turn signal switch (to illuminate the gear selector) that is connected to dimmer circuit.

Yep, i think you might be onto something. I'm wondering if I have a wire rubbing inside there connecting the two circuits. Time to tear the column back down i suppose. I took my indicator off and I can tell the little bulb is flashing with the turn signal (very faint due to only 2v)

I'm not sure what else it would be besides this? It's definitely not a full 12v.

 

[Oldtimer]

I don't have a schematic available, but there should be a single wire in column connector that you could pull to disconnect gear selector lamp. Would tell you if issue is in column wires, or elsewhere.

 

[1buckeyefan1]

I don't have a schematic available, but there should be a single wire in column connector that you could pull to disconnect gear selector lamp. Would tell you if issue is in column wires, or elsewhere.

Yep, i found that wire on the column. I actually had it disconnected (had forgotten about the bulb....since i'm using the Dakota gear selection screen). I plugged it in during testing and it now flashes with Right turn signal engaged.

The interesting part is that the bulb only lights up (gets the small 2v) only when connected. I was expecting it to flash even when unplugged if the turn signal / cam was errantly feeding it (and that circuit)?

 

[DirtDonk]

Double check that your right hand headlight and especially turn signal socket have a good solid ground to the core support.
Not only that, but after all these years, it’s probably time to “re-ground” the core support itself anyway.
Run a small jumper wire between the core support and the passenger side fender. That’s near where the body ground should be anyway.
You do have a dedicated body ground from the battery, correct?

 

[Wild horse 75]

Grounds grounds grounds. That 2V is a ground that has too much resistance. It’s using the dimmer circuit as a ground.

 

[1buckeyefan1]

Double check that your right hand headlight and especially turn signal socket have a good solid ground to the core support.
Not only that, but after all these years, it’s probably time to “re-ground” the core support itself anyway.
Run a small jumper wire between the core support and the passenger side fender. That’s near where the body ground should be anyway.
You do have a dedicated body ground from the battery, correct?

Yep, dedicated ground from battery to firewall.. where i mounted a stud to run my dash, etc off. Pretty sure I added the one to the core support tooo. I'll double check the ground on the fender (inner or outer?).. I dont recall having one there. I have deleted my marker lights on all 4 corners as well.

Grounds grounds grounds. That 2V is a ground that has too much resistance. It’s using the dimmer circuit as a ground.

Yeah, I sorta figured it was a ground issue based on the small voltage. was puzzled though how it was getting into the dimmer circuit. Am I safe to start with looking for grounds related to the right turn signal? I have already disconnected the front turn signals. going to look at tail light buckets next and try what Paul suggested.

I thought my dash was pretty well grounded. Everything is fully painted up and powdercoated now, so I've been working to scuff up some bare metal wherever I have grounds.

 

[Wild horse 75]

Check all your signal light grounds. Check your headlight grounds as well. You may even want to add wired grounds to the light buckets for your front signals and taillights. Contrary to popular beliefs sheetmetal and frames aren’t the greatest grounds. They work very well but copper wire to localized point all run back to the battery is best. Especially when you powdercoat stuff. You can get a sort of ground through paint but you won’t get that through powder.

 

[Jdgephar]

Yep, dedicated ground from battery to firewall.. where i mounted a stud to run my dash, etc off. Pretty sure I added the one to the core support tooo. I'll double check the ground on the fender (inner or outer?).. I dont recall having one there. I have deleted my marker lights on all 4 corners as well.


Yeah, I sorta figured it was a ground issue based on the small voltage. was puzzled though how it was getting into the dimmer circuit. Am I safe to start with looking for grounds related to the right turn signal? I have already disconnected the front turn signals. going to look at tail light buckets next and try what Paul suggested.

I thought my dash was pretty well grounded. Everything is fully painted up and powdercoated now, so I've been working to scuff up some bare metal wherever I have grounds.

Check the front bulb and rear bulb for good grounds. If you want to isolate it, take the bulb out of the socket in the front, and then the rear bucket and see if it goes away.

Sent from my SM-S916U using Tapatalk

 

[Broncobowsher]

Front and/or rear turn signal bulb ground.

When the turn signal goes on, the heavy filament gets power. Weak ground (Bulb, socket, wire, etc.) lets the voltage rise on the bulb's base. That rising base voltage goes through the light filament back into the parking light circuits. The parking light circuits are tied to the dash lights in the headlight switch, difference is the dash lights go through the dimmer.

And that is the convuluted path that gets you 2V at the dash lights with the turn signal on.

 

[1buckeyefan1]

Check the front bulb and rear bulb for good grounds. If you want to isolate it, take the bulb out of the socket in the front, and then the rear bucket and see if it goes away.

Sent from my SM-S916U using Tapatalk

Front and/or rear turn signal bulb ground.

When the turn signal goes on, the heavy filament gets power. Weak ground (Bulb, socket, wire, etc.) lets the voltage rise on the bulb's base. That rising base voltage goes through the light filament back into the parking light circuits. The parking light circuits are tied to the dash lights in the headlight switch, difference is the dash lights go through the dimmer.

And that is the convuluted path that gets you 2V at the dash lights with the turn signal on.

Check all your signal light grounds. Check your headlight grounds as well. You may even want to add wired grounds to the light buckets for your front signals and taillights. Contrary to popular beliefs sheetmetal and frames aren’t the greatest grounds. They work very well but copper wire to localized point all run back to the battery is best. Especially when you powdercoat stuff. You can get a sort of ground through paint but you won’t get that through powder.

Yep, you guys nailed it. It was the right rear tail light bucket. pulled the bulb and i lost the voltage. tightened the bucket down a bit (still in primer) and it's gone. thanks for helping narrow it down!

 

[DirtDonk]

Great, fine! Good detective work.
Now on to the next gremlin!