Okay, I have used the search function for this site and there are an unbelievable amount of folks who have had the same problem I've had. I've got my dad's truck roadworthy (for the most part). When I started it the other night, I noticed the cluster wasn't illuminated. Here are the lights that do work:

1. Dome Light
2. Light under dash on drivers side
3. Blinker lights
4. Seat belt (red) light
5. Bright light (purple) light
6. Headlight/Windshield wiper light
7. Temperature controls

The left turn signal actually isn't working right now but I feel like that may be something to do with the turn signal switch, since I have to wiggle it when turning the right turn signal on, to get it to work.

So, just to eliminate it being an issue, I bought a new headlight switch this morning. Of course, that didn't cure my problem. So I started tracing the issue. And before anyone asks, yes, I have the headlight switch turned all the way counter-clockwise. The old switch wouldn't dim the headlight/windshield wiper bulb at all, the new switch does, so not a total loss. I know the blue w/ red stripe wire leaves the headlight switch and goes to the fuse panel. There, it hits a small 3 amp fuse. Now, according to what I've read from fmc400, this wire leaves the fuse box the same color. But when I pulled the fuse panel from the firewall, it is not blue w/red but some sort of grey double wire with an orange or brown stripe on one side and red on the other (I'll attach a pic). With the headlights on, I had ~11.5 VDC on both sides of the fuse. While checking, I discovered the power comes in on the top (blue w/red) and leaves on the bottom (gray w/orange & red).

I'll attach a pic of the back of the instrument cluster. Unlike many I've read about, this one is in fantastic shape. Sturdy, clean and the contacts all appear to be clean and in good shape. I have replace the bulbs with brand new bulbs and have also bent the little contacts up in an attempt to get a better connection with the board.

Now, when I pulled the wiring harness from the back of the instrument gauge cluster, I had 11.5 VDC on three of the pins on one side and the same on voltage on one of the pins on the other side. They are numbered 1-9 on one side and 10-18 on the other. I didn't notice this until I looked at the pictures on the computer, so I don't know if these numbers have any significance in the grand scheme of things. I also had already put the dash back together before I took the fuse panel off of the firewall, so I don't know if the gray wire on the output side of the fuse slot is in the wiring harness or not. I was also dialing in the carburetor today and needed to take it for a drive, so I put everything back together in order to drive it. If someone knows what voltages feed what items in the cluster, that would be great. I know my fuel gauge works and the bright light illumination works as well as the temperature gauge. Didn't see much movement, if any, on the oil pressure gauge when I took it for a drive.

The only other thing I read from the many posts I looked at was that, if I am using the ground from the original radio, this could possibly be causing the problem. Presumably because of the way the old radios were grounded. I'm not too sure. I'll have to go outside tomorrow and see if my dad ran his own ground wire to the chassis or if he utilized the old ground from the original radio.

If I forgot anything, please let me know. I'll be back at it in the morning.

 

Always check the grounds!

Those numbers on the 18 pin connector do indeed have a significant purpose.

Off the top of my head...#9 (BLACK) is the cluster ground. #10 (BLUE/r) is the cluster lights. #1 (RED/y) is HOT in RUN...#12 (RED/o) is always HOT - #11 (YELLOW/b) is always hot - ammeter.

I don't have the time now for more concentrated exhumation of the wirirng, mebbe later today.

Good luck.

 

Pull the bulb holders with bulbs that are not working. Pull your new bulbs. Clean the contacts with fine sandpaper. To clean the bulb contacts in the holder, I use a fingernail sanding board, cut down to fit in to the contacts. Use a small screwdriver to bend those contacts in slightly. Next, get your battery charger out & test the new bulbs. One lead to each side of the bulb, make sure your new bulbs are good. Just because the bulbs are new doesn't mean they are good, test them. Install working bulbs into your bulb holder, then hook leads from charger to contacts on holder. If the lights don't come on, wiggle the bulb in & out a few times to see if they will come on. You may have to spin the bulb 180 degrees in the holder to get it to work.

Once you have the bulbs in the holders tested & working, move to the cluster.

Polish ALL the contact areas on the cluster with fine steel wool, including where the plug goes. Get the contact areas shiny!! Then, using alligator clips, connect to the cluster plug printed circuit (not the plug connected to the harness) at # 9 & 10. Hook leads to your battery charger & see if the dash lights come on. You may have to turn the holders slightly to get the lights to come on. You may have to turn out the lights in the room you are working in to see the dash lights, they are really dim. Take the cluster apart & remove the blue domes over the bulbs to brighten things considerably. dash lights should be working, unless your PC has a break in it, but yours looks good in the picture.

If the dash lights work, move to the harness plug.

Connect a volt meter to # 10 on the harness plug. Ground the other lead to your volt meter. Turn on the headlights, you should see a minimum of 11 volts. Since your wiper headlight light works, I suspect the power to the cluster is going to be good. Plug the cluster in & see if you have dash lights.

Most of the cluster grounds thru the # 9 ground, since you have other lights that work, your ground is good. Brake light in the cluster does not use that ground, it uses the # 1 & 4 terminals.

Check the pic of the bulb holders, a new bulb won't help. Broken contacts, lots of corrosion.





TEST the bulb & holder! Know they are good & working!! Then install them in the cluster. How to test your oil pressure gauge, or any of the gauges, in the picture. Wiring leads, hooked to the studs on the back of the gauge, other ends to a 1.5 volt battery. Reverse the leads if it doesn't work, the polarity has to be right. Gauge can be in the cluster when you do this, pop the plastic cover off that is over the studs. Use a really dead battery for the amp gauge, it works on much lower voltage than the other gauges.

 

Wow, I am sitting out in the truck reading this and I got to the part where you said something about reversing the leads on the oil pressure gauge. There were no leads attached to the back of the panel at all, besides the speedometer and the 18 pin harness. Are there supposed to be wires hooked up to the back of the oil pressure gauge as well as the battery gauge? That would explain a lot about those at least. Does anyone know what colors the wires are to those gauges or have a diagram handy? I think I saw one in some previous searches, I’ll see if I can find them.

Thanks!

 

The leads on the oil pressure gauge are only for TESTING the gauge, they are NOT part of the wiring harness. They are the leads shown in the picture above with the fuel gauge.

The gauges are all hooked up thru the printed circuit on the back of the cluster.

Hook leads up to your oil gauge as shown in the picture, other ends to a 1.5 volt battery. Gauge will move if it is good, you may need to reverse polarity when you test the gauge. Out of 50 gauges, maybe 2 or 3 will be bad. Usually the problem is the sending unit, or the wiring where it plugs on to the sending unit.

 

Scott Scott, thank you for the clarification. When I get the dash back apart, I’ll give it a try and see what I got.

Thanks!

 

Which sockets are for illumination?

I'm assuming 4 & 5. I missed one today when I was fixing a bad light and putting in a LED.

 

4 should be for your high beam indicator. 5 has no bulb or hole for a bulb if you look.

I believe the only bulbs that actually illuminate the cluster are 3 & 6.

2 & 7 should be the blinkers.

1 & 8 will be a few different things depending on what gauge cluster you have. On my '77 they're fasten seat belt light and brake light. On my '75 I believe they're brake and low fuel economy lights. This is going from memory and looking at the back of the cluster of course.

 

I wasn't sure if 5 was for a light or not since the odometer is towards the bottom.

I'll try 3 or 6 tomorrow. Right now I've got half blue and half green dash. I don't drive much at night so I'll probably never see it but the main thing was I got my blinker light fixed.

Thanks.

 

What I found and your printed circuit board looks to be D6TF10C956

 

 

Has anybody reading this thread tried a little dielectric grease in their dash connections with good results? Seems like clean corrosion-free contacts solve a lot of problems the more I read on this site. Asking because I'll need to get into my dash soon like OP.

 

If that question is directed towards me I have an aftermarket radio. But since I kind of hi-jacked this thread you might have meant it to the OP.


My problem was one of the original bulbs had gotten hot and partially melted. That caused it to not fit in the socket very well. I'm not sure that dielectric grease would help much.

 

 

[QUOTE=Djstright;17853773]Huh. That's interesting. Ya I wired in my radio but for ground I ran its own ground wire directly the the cab body. I only pulled + keyed power from that radio connector. There is another wire, blue/red stripe on that connector but I didn't look up what the wire is for but I was pretty sure it wasn't ground.

Just checked my wiring diagrams, yep blue/red is dash illumination. Awesome, that lets me know where to hook up the illumination wire for my aftermarket tachometer