CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

Headlight Dimmer Switch Wire

Chief Brody

"Amity Island Welcomes You"
 Premium
GMOTM Winner
Joined
May 18, 2010
Posts
9,606
Reaction score
1,980
Location
Alabama
I have power in the dark green wire at the headlight switch. As best I can tell, that wire goes through the fuse block and ends up as a gray
wire(s) at the instrument cluster harness.

I have no power at the gray wires in the instrument cluster harness.

instrument harness.JPG
 
What I did:

1. Traced and connected green temp sending wire to sending unit
2. Ran new wire to fuel sending unit
3. removed orange/white wire to fiberglass top from fuse block Accessory spade
4. clipped messy bundle of radio wires (4 wires yellow, black, 2 gray)

result = dash lights no longer work
 
Chief, I'm tied up for the next couple of days, and have to get up early tomorrow, so I'm not going to be much help.

But, you need to check your fuses. One of those gray wires goes straight to a fuse.
I suspect if you have no fuses blown, its going to be one of those gray wires you cut.
You might have to replace it if it went anywhere, or maybe tie the two together.

I'm off to bed, but I will check in tomorrow when I can.
 
Chief, I'm tied up for the next couple of days, and have to get up early tomorrow, so I'm not going to be much help.

But, you need to check your fuses. One of those gray wires goes straight to a fuse.
I suspect if you have no fuses blown, its going to be one of those gray wires you cut.
You might have to replace it if it went anywhere, or maybe tie the two together.

I replaced all the fuses in the fuse block today.

I also tried twisting the two gray "radio" wires together, thinking they might be the dimmer wires...no luck.

the only place I haven't looked is behind the fuse block.
 
OK, Chief, this is the last time. Seriously. I am going to fall asleep in the audit tomorrow.
I was asleep, but the damn circuit kept bugging me until I woke up and realized I would not be able to go back until I figured it out.

So, here it is.
The schematic I am including, IS NOT fully trustworthy. Its for a later model and I do not know what may have changed.
But, it does have some advantages over the ones we have.

DO NOT look at it yet.
Instead, use the 73-76_cab_ inter schematic for now.

Here is how your truck dash lights work.

Power for the circuit comes in on 16OR-40C on the headlight switch.
When you turn on the lights, the power comes from that contact and goes to 18BRN-9. That contact also supplies power to the rheostat that dims the instrument lights.

At this point, I want to stop and ask if you are sure the lights are not turned all the way down to dim.......

If your parking and clearance lights come on, then power is getting to the 18BRN-9 contact, because that is where it goes.

The power flows though the rheostat and into the 16DG-44 wire. If you like, you can check it there on the head light switch.

That wire then goes to the fuse block, not the firewall connector. It hooks to one side of the "inst lps" fuse.
The other side of that fuse has the gray wire hooked to it.

NOW look at the new schematic. I'm pretty sure that the dash light circuit is the same.
Note in the lower left corner of the fuse block. There is the 44 circuit on one side, and the 8 circuit on the other of the "inst lps" fuse.

Also note the front numbers have changed. The front numbers have always been the gauge of the wire, and I guess they went metric this year.

Anyway, follow the gray 8 wire up to about the middle of the page. There you will find a large splice.

If you turn on the headlights, turn the rheostat all the way to max, and have power to ground on both sides of that "inst lps" fuse, then I bet its going to be that splice.

Either way, if you have power at that fuse, then its going to be from that fuse to the panel plug you took the picture of.

Happy hunting, let me know what you find.

77-80_instrument_pg2.jpg
 
I've accidentally pulled a black ground wire off that grounds near the E-brake lever on my old trucks while doing a radio install,and the dash lights would not work afterwards,till I found the dissconnected wire and grounded it again...I guess it grounds the instrument cluster...and its not always shown on a wiring diagram!..
 
First, thank you Fordum...I really appreciate all your help and schematics assistance...if you were close enough I'd drop off a 12 pack of ice cold beer.

I found the problem...I haven't fixed it yet, but I found where the problem is...the fuse block.

I was tracing the two gray radio wires back to the block when suddenly the dash lights just came on...

I tapped the fuseblock with the scewdriver handle and they went off again...so I guess I have to loosen the fuseblock screws and look at the backside.

what will I see on the backside? are there connections on the back or do I have to replace the fuseblock?
 
Hmm, sound like there is bad connection. Before you pull the fuse block, pull the fuse and make sure it is "okay". Sometime with the old glass fuses, the fuse looks okay, but there is actually a break at the ends. This threw me for a loop one day till I tested the fuse.
There also the spot were the fuse goes could actually be corroded. Clean these spots.
I had a friend who fixed a lot of his electrical problems by spraying his whole fuse block with PB blaster. Not something I recommend.
 
Hmm, sound like there is bad connection. Before you pull the fuse block, pull the fuse and make sure it is "okay". Sometime with the old glass fuses, the fuse looks okay, but there is actually a break at the ends. This threw me for a loop one day till I tested the fuse.
There also the spot were the fuse goes could actually be corroded. Clean these spots.
I had a friend who fixed a lot of his electrical problems by spraying his whole fuse block with PB blaster. Not something I recommend.

I put all new fuses in, tested each end for power...all is good as far as the front of the fuseblock...there is some corrosion but it doesn't appear to be affecting the fuses...don't know about the back...it could be eat up.
 
what will I see on the backside? are there connections on the back or do I have to replace the fuseblock?

Darned if I know. My knowledge of fuse blocks is on a par with the dirt question I got asked when I wanted to know if I could grow a certain crop at my farm.

He wanted to know what kind of dirt I had.
I told him as far as know, its just the regular kind of dirt. At least it just lays there and is pretty darned polite about it.

When it comes to fuse blocks, its the same way. Most of them just hang there and do their job.
So I never really had a need to disturb them.

My one and only time working on one curiously enough was a Chevy. No one ever believes me about it, because the guy is dead and I have no other witnesses.
They think I made it up from that joke.

I was hunting with another club from my usual bunch, when we lost a guy.
He was not where he was supposed to be, and we could not raise him on the radio.
Then, he came on and said he had an electrical problem, that killed his radio and engine.
He had gotten it going, temporarily, and was on the way.

He was just telling us where he was, when we heard what sounded like the beginnings of a gunshot and then the radio went dead.

I was closest, and went to find him. Found him sitting on the side of the road, with two beer cans on the ground and working on a third.

None of the bunches I hunt with drink anything while hunting, so I was surprised. But he looked white as a sheet.

I walked up, and he pointed at his fuse block, which was scattered all over the inside of the cab.

It seems that a wire came loose and blew a couple of fuses. He replaced one, but needed another to get the truck going.
He thought he had fixed the loose wire, so he looked around and found a .22 cartridge and put it in the fuse holder.

Trouble was, he had not fixed the short.

When he hit a bump, another wire shorted, and the .22 fired blowing the fuse block all to pieces.
The casing, being lighter, did most of the traveling.

I found the original short, tied enough wires together to make the truck run, and got him home.
I promised him I would not tell what he had done, so no one else ever knew.
He pulled the fuse block off an old junker he had at his house, and hooked it back up.

I forget what he told them happened, but he got away with it because no one else ever saw the block.
They all just thought it melted or burned up.
 
I think maybe he shot the fuseblock...I'm not sure electricity will ignite a centerfire cartridge...doesn't it take an impact to the primer?

Anyway, I am not in danger of that scenario...I carry 30.06...won't fit in the block :eek1:

McGuyver would have taken out a stick of DoubleMint gum, chewed the gum and rolled the foil wrapper into a make-shift fuse...:haha:

I stand corrected...I saw the video....
 

Latest Posts

Top Bottom