gauge diagnostics [Found the issue, now the fix?]

[metalneverdies]

After my 5.3 swap none of my gauges are working. My voltage gauge worked for a couple hours but now it also doesn't work. The thing is the voltage gauge wiring is the only one that was changed.

Does any one have any advice on diagnosing the gauges on an 87 k5 with TBI? All the dash lights work. Just none of the gauges read properly.

 

[4X4HIGH]

Senders are specific to the gauge so you would need to swap over all the senders from the TBI engine to the 5.3 engine.

 

[metalneverdies]

Senders are specific to the gauge so you would need to swap over all the senders from the TBI engine to the 5.3 engine.

I did. Fuel sender and oil press are from tbi. Volt meter was run off the alt output post. Did it possibly see too much amperage and fry everything?

 

[dyeager535]

Amps are draw, that wouldn't be the case with a gauge unless it had an internal issue to start with.

With most swaps, wiring is the problem. If none of the gauges work, I'd be looking at the +/- to the cluster. Whether it be the actual voltage/ground feed for the cluster, or the cluster connector itself.

Voltmeter obviously only need power and ground, if nothing is working now, then I'd check those two first. Hopefully your dash is apart a bit, the cluster is kind of a hassle to get out if everything in the dash is in place.

 

[metalneverdies]

Amps are draw, that wouldn't be the case with a gauge unless it had an internal issue to start with.

With most swaps, wiring is the problem. If none of the gauges work, I'd be looking at the +/- to the cluster. Whether it be the actual voltage/ground feed for the cluster, or the cluster connector itself.

Voltmeter obviously only need power and ground, if nothing is working now, then I'd check those two first. Hopefully your dash is apart a bit, the cluster is kind of a hassle to get out if everything in the dash is in place.

I am going to have to pull it all apart.

If I ground my oil pressure gauge and fuel sender gauge they should both read full/max, correct? Unplugged not grounded would be empty/low, correct?

 

[dyeager535]

I can't remember which way is which, but yes to ground/open, but that is on the sending unit wire, not the gauge +/-. Three wires for all gauges except voltmeter.

*Normally* for the oil pressure/temp guages, if the power/ground is good (so sending unit/sending unit wire issue), the needle will move to something higher than minimum reading after you turn the key off, and once you turn the ignition to accessory, they will then go to minimum reading.

But since your voltmeter isn't working, either the gauge has actually failed (highly unlikely) or there is something wrong with the power/ground to the cluster.

I don't know about 1987, the earlier (~1985) clusters had multiple +/- leads going to them, so it was possible for certain things to work even with a power or ground issue. At some point (at least as early as 1990 on the R/V trucks) GM simplified the cluster wiring and went to single +/- to the cluster.

 

[metalneverdies]

Hmmm. My volt meter was working then went to below min voltage.

My fuel gauge was reading half till after about a 40 mile test run and oil was max and Then dropped down to around 15 psi. None of the gauges moved around except for dropping to the next point then never moved again.

Fuel usually bounces around and no longer does. Even with adding 15 gal gauge dint move off of lower than the empty marker

Must be power / ground to the cluster.

 

[dyeager535]

The cluster wiring on these is crap, which is why I hardwired mine. When there is a constant problem like yours it is easy to solve, but the intermittents are the real annoying ones.

Even after fixing the problem, the cluster design is so bad that it's likely you'll have problems later. All the gauges except the cable driven speedometer are (IMO) incredibly well made, hard wiring the cluster solves the only real failing that is inherent in the design.

 

[metalneverdies]

You mean removing the printed circuit and replacing it with individual wires?

Sounds like quite an task. The only diagram I have seen for these dash setups are a nightmare. So hard to trace out. Wish there was a good simple diagram made for these.

 

[dyeager535]

Yep, the printed circuit "board" is the problem. The terminals don't always make good contact, and yes, it is a task to work around. But once done, the cluster should never be a problem again.

They aren't really complex once you look at them closely. Every gauge has +/-, and those can all be common (which is what GM eventually did). Earlier clusters had two or three +/- feeds to the panel for some reason. Every gauge but the voltmeter has a signal wire specific to the respective gauge. All panel lights tied into the headlights can share common +/-.

All the indicator lamps (high beams, check engine, brake, seat belt, turn signals) use a single additional "signal" wire, which is either a switched + or -, depending on which indicator lamp it is.

When you pull the cluster and look at the PCB, you'll see that you can easily trace the circuits, and you'll see that most of it is common, only the signal wires aren't, and at that point it makes a lot more sense.

 

[metalneverdies]

So I finally got the stupid gauges pulled out of the dash. I kept having to quit because I was getting frustrated and the old plastic tabs kept cracking. After quite a bit of wiggling it finally came out.

I measured the gray wire that the headlight switch is supposed to power and it is only getting between 4 and 5 volts. I would assume it needs 12v.

None of the pink key 12v+ wires are getting any voltage at all. The Ign lamps fuse is also only reading 5v with head lamp switch on, reads 0v with switch off.

Any ideas on a fix? I traced the connector according to the post below, Most of the wires seem to match. There is a double pink wire on pin 18 that doesnt match. Other than that I have no idea what to do

http://coloradok5.com/forums/showpost.php?p=3049627&postcount=13

 

[dyeager535]

Just to clarify, you are measuring at the actual cluster plug, not trying to measure on the circuit board, right? Assuming yes...you are also using a chassis ground to test, not the cluster ground right?

If all that is a yes, I'd start with the headlight switch. That would be 12V, why you aren't getting 12V there would be a concern, and it's a lot easier to deal with (and independent of) the ignition switch. I'd check voltage coming off that pin at the headlight switch.

Your headlights work though?

 

[metalneverdies]

Just to clarify, you are measuring at the actual cluster plug, not trying to measure on the circuit board, right? Assuming yes...you are also using a chassis ground to test, not the cluster ground right?

If all that is a yes, I'd start with the headlight switch. That would be 12V, why you aren't getting 12V there would be a concern, and it's a lot easier to deal with (and independent of) the ignition switch. I'd check voltage coming off that pin at the headlight switch.

Your headlights work though?

I was grounded to the parking brake bracket. Yes, I was reading the voltage by back probing the connector. Yes, headlights work fine. Park, headlights, and brights.

The dash back lights worked before I pulled the cluster out so that makes me think the headlight switch is operational?

Ignoring the head light switch for a second ( I will still check it). Where do the key 12v + wires originate that run up to the gauge cluster? I had the key in the run position and they would not read voltage.

 

[dyeager535]

I don't have my diagram in front of me (plus it's a '91 so might be different) but I would assume that the ignition wires come out of the fuse panel off the gauge fuse? I don't believe they come off the actual ignition switch since they should be fused.

The voltage wire from the headlight switch should also vary voltage as you turn the headlight knob, but should be 12V down as you dim it of course. All the bulbs are 12V, so at 5V they should work, just be dim.

 

[metalneverdies]

Hmm. Maybe I missed it last night but I didnt see a gauge fuse. I have been trying to google some quality diagrams. I will see what I can come up with.

 

[metalneverdies]

I found some pretty good old wiring diagrams for an 86 k truck. It seems all the pink/black wires that should be key 12v+ go to a splice. looks like it should be circuit 39.

I just have no idea where the splice is. It looks like the splice is coming from the fuse block. Top left corner. I will have to check.

 

[dyeager535]

Yeah I believe the later ones like I have (with TBI) aren't going to be exact, even though the physical panel design is the same. At least back to '85 they were the same.

 

[metalneverdies]

After hours of tracing circuits and diagrams I figured out what is causing the fuse to blow! When ever the transmission connector is plugged into my 700r4 the gauge/idle fuse will blow.

I replaced my stock TCC internal trans parts with a lockup kit from bowtie overdrives. I did NOT change the wiring for the wire on the 4 pin plug that gets power when I apply the brakes. The wire that is plugged in is Purple and i believe pin # 24 on the engine side of the bulkhead connector.

Any ideas? Every diagram that I have looked up shows circuit 39 to be the key 12v + from the gauge/idle circuit. I didn't see anything about the TCC stuff on that circuit.

EDIT:


After more research I am positive it has to be pin #24 purple wire that is hooked up and causing issues. Makes no sense, from the factory that wire was plugged into my trans. According to every diagram I have looked at that should be going to the backup switch if I had a manual transmission. Other wise its "not used". I am completely lost now. The wire gets 12v when the brake is applied; so that would rule out that is is for a backup switch.

 

[dyeager535]

If it's auto trans stuff, someone who is smart on them is going to have to chime in.

If you don't have your year GM factory service manual/wiring diagram, the diagram has to be questioned. GM made changes almost every year, this is why Haynes/Chiltons suck. When needing very specific wiring info they will let you down every time. There is no "typical" on these trucks

 

[dyeager535]

Why did you convert to the Bowtie overdrives setup? Unfamiliar with it, but probably just need to retrace steps from the install. That ppl wire go straight to ground inside the trans now perhaps, the Bowtie internal wiring not correctly matching up to the TCC connector wiring?