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Instrument Panel Wiring Info Needed!!

Bross82

Bross82

1/2 ton status
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Feb 11, 2002
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Spencer, MA
I am replacing ALL the gauges with autometer gauges and am going to bypass using the printed circuit that the original gauges use. I asked for a wiring diagram in another post i found. But, if this is the same as what is in the Haynes manual, I don't think it will help me much. Does anybody know what each wire does that goes into the wiring harness that hooked up to the printed circuit? There are roughly about 16 individual wires going into the back of this, and each go into a numbered location.

The dash has been torn apart for a while now, just been waiting on figuring out why my fuel gauge reads out way past full. I replaced the ground wire today, and wanted to test that before running a full new wire to the sending unit. I traced along the printed circuit to where they would meet up with the fuel gauge. I believe it is only the 1st wire from the top and the 3rd wire in from the top on the right side of the harness (maybe number 11 and 13? (if it helps, I can go find out what these numbers are)). I put individual U shaped connectors on the end of each wire and put them on each post of the old gauge. Before when the dash was together, it'd read way past full. Now, there was just nothin. :doah: The needle didn't move at all. Also, one of these wires is green, and one is pink (there were multiple pink ones). The pink one oddly went from the third spot on the right, and into the bottom right (possible 16th possition on the wiring harness) with some other pink wire coming out.

Thanks for any help!
 
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ok..so i hooked up my fuel gauge to test it out, and now it reads at about 5 o'clock, whereas with using the printed circuit it read at 3 o'clock all the time. I changed the ground wire from the sending unit to the gas tank, didn't change the wire from the sending unit to the gauge yet. Does it matter if I use one of the ground wires from the wiring harness to the fuel gauge or should this be grounded to the gas tank since I'm bypassing the stock setup?

Also, I individually wired up the voltemeter and it reads way past the max charge. It does show a change in its readings when something is used that draws power, such as starting the engine or using power windows, but then it jumps right back up. This probably shouldnt even read on the high end within the normal readings since the trucks been sititng a while.

I think I did get the temperature gauge working correctly. So I think its down to these two gauges (the oil pressure gauge has been swapped out to a mechanical gauge, and I ran a new speedometer cable).

Thanks
 
Fuel gauge only needs the pink (typical) wire from the tank. You can ground and power the gauge from anything, probably best to use the wires that were on the old connector of course.

Problem with gauge wiring diagrams in haynes, etc., is that they are too generic for things like the cluster that changed the wiring pinouts over the years.

As to the volt gauge, you've checked that it's not actually reading system voltage correctly with another voltmeter?
 
For the fuel gauge, I did see the pink wire when i swapped out the ground wire. But, when inside the cab, are there two tan/white wires that you are supposed to use? According to the diagram in the link above for an 85, the Tan/White is to the Fuel Gauge Tank Unit. These two wires went into the same pin location on the printed circuit connector. So I guess then, am I using the correct wires once inside the cab?

For the voltemeter, i haven't tried with the other new gauge if thats what you mean. The only gauge that didn't seem to work before was the fuel gauge. It went to a 3 o'clock position and just stayed there. But, the same thing happened with the new gauge, so it shouldn't be the gauge for that one. But, back to the voltemeter, I think I can get a hold of one of the testing voltemeters if thats what you mean. How would I correctly go about testing this? Hook the meter up to the 12v wire I was using and ground also? Then, test the direct source and hook it up to the battery and ground?? :confused:

Thanks
 
According to that '85 diagram, don't use the pink for fuel gauge. :) Looks like tan/wht is it. In mine it's pink, but I'm not even sure what year my harness is, something after 1984 I believe. Things changed, or I may have had to run that wire myself. It's been awhile since I did that wiring in the truck.

Voltmeter as in a separate tool that you can use to measure DC voltage. You can test it where the gauge goes or simply at the battery, + and - terminals. Shouldn't be much difference in the readings. Test with engine on and off. You can test the alternator output by touching one of the probes to the single wire ring terminal on the back of it while the other probe is grounded, but again, should be very near what you see at the battery. If it's overly high at the alternator, it will be everywhere else you test. Anything over about 12.5 and under 14.4 is pretty good at idle, but you should test with heater on high and headlights on as well if you want to verify that output keeps up with the increased load.

That wiring diagram almost looks like its for idiot lights anyways, not gauges. I don't see an oil pressure sender, and that is typically a brown wire. Small point, but gauges/non-gauges makes a difference in the wiring schematics.
 
so i guess the next thing for the fuel gauge is to try replacing that wire from the sending unit on the gas tank. If i wanted to test and just run straight from the sending unit into the gauge in the cab, is there any reason why there are two wires in the cab? i just think its weird there is only one wire coming from the tank, but randomly two in the cab.

Well, as far is this diagram....this one isnt even exactly right. But is a lot closer than the Haynes one. The green wire seems to be right for the temperature gauge. But, this diagram shows a brown wire for the alternator. There's definitely no brown wire on this connector. Only thing thats kinda brown is the tan one that is listed as the Oil Pressure Switch. The tan one is in the center of the connector on the diagram. Is that the oil pressure sender wire you were talkin about? Thankfully, since the electrical gauge gave me problems a few years ago its now a mechanical one, so I don't have to worry about that one as much. If the voltemeter can just be set up with a 12v wire and a ground, why would you need the brown wire that's listed for the alternator?

I was going to just straighten out one thing at a time. But I guess I'll mention also now without this connector hooked up, I dont seem to have my directionals, horn, or headlights working right anymore. Nothing at all has been changed besides individually wiring things from this connector and not having that hooked up to the printed circuit. Is that supposed to be tied into this cluster like that? I see in that diagram the directionals listed meeting up with their respective wires from the direction/horn switch. Aren't these only to light up the indicators on the dash? I find it hard to believe if that indicator went out that it would take one of these out with it. Anyways, before, I tested hooking up the light green one to a small light and grounding it. The light didnt come on. But, when I think the high beams should have been on, only the headlights were on. When I clicked to what should have been turning off the high beams, the headlights went out and still no high beam lights either(i have the 2 vertical headlights on each side). BUT, I do have all the directional lights lit up, and the tail lights. Also, the hazards make all the directional and tail lights flash. It's just the horn, headlights/highbeams and turn signals that don't work right.

Thanks
 
I definitely agree with doing one thing at a time. If you wire up all the gauges, it will only guarantee that at least one will be messed up when you turn the ignition. :)

Some of the confusion on those printed circuit boards probably comes from the fact that there are multiple grounds and 12V feeds.

Instead of wasting time trying to replace the wire to the tank, if you've got the wiring, just bypass it for testing. There is a connector near the tank, and you can just wrap the wire around the correct terminal on the gauge itself. Either that or you can just disconnect the wire from the tank connector and (with a multimeter) make sure the wire has continuity from that connector to the gauge, and that the wire isn't shorted to ground. (the body, frame, etc)

If you put the fuel gauge needle at say 1/2, then apply power and ground (either with key on or just get 12V from a batt. source) to the right terminals, with the gauge sender wire disconnected, the gauge SHOULD peg out. You may need to give it awhile, GM says that some of the gauges can take awhile to move full sweep.

Dunno about the alternator wire, I thought an alternator wire was only for the old trucks with an ammeter.
 
ok, i figured out what wires are for what. But I'm not sure what the panel light fuse is for? This panel light fuse looks like its for something different, not for the instrument lights, and i dont know what...the gray wire is for the instrument lights, this panel light wire is pink (it's not the 12v wire which is pink with a black stripe).

I think I figured out why the headlights stopped working. Maybe the connector to the light switch was loose? i didnt really do anything except for what I was messing with for the wiring from the one connector for the dash gauges and lights when they stopped working. I didn't touch the wires for the headlights. But, i tried disconnecting the headlight connector that connects right behind the light switch/knob and reconnected it and now they work.

I also ran a wire straight to the sending unit, hooked up the 12v wire and the ground. It pegged out right away at about the 3 oclock position. Removed the wired from the sending unit and the same thing. So, I'm guessing I need a new sending unit?

Thanks
 
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