Instrument Cluster Lighting Issue

I have 1986 F250 king cab 2WD. The dash lights and turn signal lamps stopped working. The gauges work fine. The switch for the headlight/dimmer was replaced. The new switch is an 8 pin the existing switch was clearly burnt up and it was a 7 pin. NAPA stated this was the direct replacement. It fits and works the headlights operate on/off but I get no instrument cluster lighting HVAC control lighting or the headlight windshield knob lighting. I removed the cluster, changed out all of the lamps to new standard incandescent. I did get teh high beam indicator to work and both turn signals. But none of the other lamps in the dash operate. The dome light does work and the exterior marker lights and headlamps operate.  I get voltage on the circuit board to the lights I describe that work but no voltage to any other lamps. I cant tell if this is a combination of a ground or fusible link issue potentially. I have checked all of the fuses and they are all good. Any assistance to steer me would be appreciated!

Welcome to the site.  But you apparently missed Jim's email asking you to go to the New Members Start Here folder and post an intro there.  Don't worry as many have missed that before.

We ask that because we host the guidelines there and since we hold everyone to them we want you to have had every opportunity to have read them.

So please read the guidelines and let us know that you have before we get into the instrument lighting discussion.

It's all good now.

Carefully look at the wires coming from the plug of the headlamp switch.
If they get overheated and melt they can short or fail open.

You can get both the 7&8 pin wiring pigtails from Pico.
https://www.picowiring.com/catalog.html

Thanks Jim! yeah I went through it pretty good. I have a new 8 pin switch. The headlights work now as do the indicators up at the cluster. Just nothing else. All of the lamps are new and I tested the circuit board on the cluster. I do not have any voltage to the pin connector or any of the lamps so I do not think it is a ground issue. Just lost power somehow. I'm heading back out now to start over..

So is it just the cluster?
Do you have illumination of the climate control, radio and headlamp/wiper switches?

If so, that points to the plug on the back of the cluster or the flex circuit.

No, the wiper knob light, the climate control lights and all of the "Blue" back lights at the cluster are dead. Just found that I have no voltage on the 5 amp cluster illumination space on the actual fuse block. I am tearing the fuse block out now. May be the source of the gremlins. Ill let you all know ! Thank you

That 5A fuse is powered by the Lb/R wire (circuit 19) coming from the wire wound rheostat on the headlamp switch.

If you don't have power to either side of the fuse check continuity from the switch connector to the panel before pulling everything apart.

ok I checked the headlight switch. When powered on it sends voltage to the 5A fuse block. The block is fine. Its after the fuse block. I traced the the power out of the fuse block into the harness. It leaves on a blue wire with pink tracer. I believe it is "supposed" to land on terminal 5 up at the cluster pin. But it has no power there or at any of the climate lights or wiper knob light. Somewhere there is a splice or relay.

If you have none of those lights it has to be between the fuse panel and splice 806.



Splice 806 is listed as (Taped Over) 'near heater control switch'

yep..thank you for the diagram! I also think I may have a bad "new" switch from NAPA. Now the blue wire with tracer that was hot when the lights were turned on is dead and so is the fuse block. So Ill grab one tomorrow to be sure. Thank you so much for your help. Ill hit it again after work tomorrow.

Before you go swapping out the light switch check fuse #4 (15A) because that would kill all your lights.

It's the tan/white feed wire (circuit 195) that usually has a pigtail meltdown.

You're hot on its heels. I'm sure you can figure it out tomorrow!  

Jim,

Well the good news is I found it! It took opening up the harness and physically tracing the instrument circuit. I located a ground wire off of an aftermarket radio harness improperly tied to the same circuit. The wire was assumed to be "ignition on" but clearly not correct. I was able to use a volt/amp meter with resistance to ohm out and trace each load which is how I pinned it down to the radio. Making some repairs to the harness is the next step. Then I get to assemble my interior. I am super happy I have lights again Thank you very much for all of the info!

Congrat's!  Well done!  

Congrats Steve!  

I'm not sure why anyone would tie a ground to that wire.
The main cab ground is right there next to the radio.

Give me a minute and I'll post the diagram....

So.... Im the idiot that did it ! Here's the best part Jim I am an electrical contractor by trade and CLEARLY know better. I removed the old radio and installed a new unit about 3 months ago. It worked just fine. However I am working on the truck and not really driving it so I never turned on the headlamps.

On the new radio harness the black and brown wire is the ignition "on" . The BLACK wire is grounded in the unit. My 52 year old eyes missed the fact I tied the ignition wire to the ground harness . I'm such an idiot.

Don't beat yourself up.

Y/B is hot in run & accy for the radio.
I assume you also need constant 'keep alive' power for settings and memory?

Correct..... the radio has both a constant hot and a trigger ignition connection. It was grounded through the frame and speakers so it worked just fine. But when the headlight switch was activated...well we all know what happened. In my world BLACK is a current carrying conductor. In DC circuitry, it is typically a ground but it can carry current as you stated when tracers are applied. I should have known better this was first year stuff. I just had brain fog. Luckily I didn't smoke anything.

If you're 52 you've probably been working with "black=hot" for 30 years.
It's no wonder your brain went there automatically.  💡
Fortunately you didn't let the smoke out of the radio or the harness.

I've been a contractor with a few cabinet shops over the years.
I'm familiar with both single phase residential and three phase (208 & 480) in star and delta for the oddball assortment of machines I've owned.
Some of those use black as neutral.
Things can get 'spicey' when you've got 40A at 480!  🤯

Ha...   yes they do. 480v is not to be taken lightly!

It's a lesson you may not live to learn!

The cigarette lighter (460 Y/LB) is hot at all times and close enough to the radio for constant power.