Hi guys,
First let me say how stoked I am to have found this forum. I just purchased my 1974 F100 this last Friday and have since been scouring this site for all I can learn. There are quite a few things that have been left unfixed over the years. On my drive home in the evening I started a mental list. Dash lights were all out. Half of the running lights were out. The headlights need readjusting. Seat needs recovering. Speedometer cable, Door panel, Dash pad, window regulator and handles etc.... Things on top of things on top of things unfortunately. Today I decided to tackle lights. I pulled the cluster, cleaned up the contacts and replaced the lamps with LEDs. Noticing the dome light wouldn't come on with the headlight switch but does with the door switch, I replaced the headlight switch as well. It works well turning on the dome now.

Where I'm running into a problem is with the dash lights. The flasher, Brake and Hi-Beam indicators work perfect and bright but the Cluster and Climate Control back lights are extremely dim. They actually flicker on and off at idle. They do get a hair brighter as the revs get higher but still are not at their regular working brightness. Here's the craziest part: The headlight switch dimmer doesn't work on them at all. In fact, all three of these lamps are coming on with the ignition switch rather than with the headlight switch.

I've been at this all day long now and finally threw in the towel and came in to post this and see if anyone could share some help. Anyone else had these issues or have an idea of how I can clear this up?

 

Sounds like an '82 Mustang GT I once had, where the PO wired a few Instrument Panel lights through a toggle switch under the dash.
Why did he do this? Because the Instrument Panel light circuit was fried.
Why was the Instrument Panel light circuit fried? Because the PO had improperly run the ground from the stereo to the gauge light lead, popping the fuse when the lights were turned on. He must've jumpered the fuse, because the Instrument Panel Printed Circuit Board was fried.
Why did the PO ground the stereo to the Instrument Panel circuit? Probably because the IP light wire (light blue) runs with the switched 12V+ for the radio, (yellow) and people mistakenly assume that it must be a ground. It's a common mistake...

So if there are any amateur stereo installations in your truck's history, this might be the correct path to pursue.

And welcome to the site!

 

I appreciate this... In looking through the wiring I've seen it all looks to be stock. Of course all it takes is this one wire. I will make sure to take a good hard look throughout first thing in the morning. Dang this is frustrating.
Thanks for the help and the welcome!

 

Pull the blue lens off the back side of the cluster, that will brighten the dash lights up. There is a thread about it on here. Use the Advanced search to locate it.

Do you see the blue line with User CP, Albums, FAQ? See the SEARCH on that line? It has a drop down search menu arrow, go to the "Advanced Search" option, top left side (search block) type in there what you are looking for and then go to the lower right column and highlight 73-79 forum. Select it and then you will have a detailed search just in the 73-79 forums.

The climate control light is not adjustable in brightness. They have one (?) bulb and the housing design only lets out a small amount of light. If you pull the panel out just a bit, no need to disconnect the 2 hard cables, you will see the bulb housing. It is small like the headlight and w/s wiper light housing. Maybe change the bulb to LED also, or dremel the hole out a bit?

The instrument cluster flasher (turning signal?), brake (warning light) and Hi-Beam lights (indicator) are NOT suppose to be dimiable. The brake warning light and seat belt light are suppose to come on when you turn the key to start the truck, to do a circuit test.

X2 on welcome to FTE, best Ford truck site on the web, hands down. Make sure you ck out ALL the RED read 1st threads, TONS of info there.

https://www.ford-trucks.com/forums/1...then-some.html

 

To suggestions - check the voltage at the bulbs using a multimeter both at idel and higher RPMs - normally your votage may be a little low at idle bt by 1500 RPM you should be up to full voltage. If it is not doing that, you may have other issues. Also, LEDs only work one way, if the + and - are reversed they don't work. For the bulbs which do not appear to work, try reversing them.

Unless you absolutely love the blue filters on the bulbs, get rid of 'em. Even regular incandescents work fine without those filters. You can see the difference between the PRNDL light and the dash lights.

 

I tried to locate the thread that explains removing the blue lens and even has pics...no luck. Anyone have that one saved?

 

I've been through the threads and videos of removing the cluster, taking it down, cleaning it up and removing the blue lenses and polishing out the Clear front lens. I did choose to keep the lenses for the time being and realize I will lose a little brightness in that decision. I understand the Brake/Hi-Beam/Turning indicators do not dim and they are all working perfect and bright.

Again my concern is with the Climate control and Cluster back lights. They all are barely on and the cluster back lights aren't dimming or getting bright with the dimmer built into the headlight switch. They stay exactly the same through the complete twist.

Thanks guys for all the suggestions you've shared so far. Keep 'em coming. I'm going to pick up a multimeter today and start going through the connections.

 

Well again I suggest that next time you have the cluster out you remove the climate control panel. 4 small bolts and it will pull right out, or at least enough for you to get an eye on the light.

I seem to remember a single light bulb fixture back there. A different bulb or some modification of that fixture might be in order?

Sounds like you might need to clean the rheostat ring contacts on the headlight switch to get the dimming capability working or just replace the switch all together.

Good info. https://www.ford-trucks.com/forums/9...l#post11039198

 

I have changed that lamp with an LED at the same time I did the cluster. Ihave it hanging down currently so I can see if it brightens up at all. It is barely on being a very soft glow looking directly at the bulb itself.

I installed a brand new headlight switch yesterday at the same time. I would think if the switch was the problem, there wouldn't be any current to the lamp. The Rheostat is a physical dimmer with a connection being made along a resistive coil. :-shrug

Thanks for putting all you thought into this.

 

Any chance you could clean the back side of the panel face (where the light transfers thru) or the front side illuminated strip of the panel? Or mod the piece that holds the bulb to let more light out? Dremel time?

Since you have a new headlight switch, I do not know what else to suggest. Might be a wiring problem in the harness?

 

Thanks a million for this last post! These diagrams will give me a good idea of how to track this down. I am indeed getting low voltage to the Climate control/Cluster/Headlight/Wiper Backlights. I swapped in a good incandescent and the element barely turns orange. No glow at all.

 

I take it you have not been here then? They are in here and alot of other stuff. My #4 post has the same link.

All the elec diagrams start on post #10. https://www.ford-trucks.com/forums/1...then-some.html

 

That is certainly a wealth of info and much appreciated. Bookmarked it for all my future needs.

 

Always near the top of the forum list in the red read 1st section. Ck out the other red threads, tons of good stuff in there too.

 

Grrr.... I don't see where anyone might have fiddled with the Blue/Red wire anywhere. I have had the complete dash apart digging around and looking. I won't be able to get my hands on a multimeter until Monday probably. What really has me wondering is the fact that they are all coming on (though under powered) with the ignition switch rather than getting power from the Headlamp switch. Is it possible that the lights are always on with ignition though at a low setting and then over ridden with power from the dimmer? Maybe the new Headlamp switch is bad?

on a secondary note.... can someone explain to me what this part is? Please excuse my ignorance but the truck is completely new to me. It seems that it has lost a considerable amount of sticky resinous material and what looks to be sand. It sits opposite the drivers side hood hinge.