BJ73/74 instrument cluster just stopped working (3 Viewers)

[badusmaximus]

Hi all,

So, I've been having difficulties with my tachometer on my BJ73. See this post for why I'm removing my cluster multiple times in the first place:

Tach issue

So the other day, I was installing the OEM hardware to attach the tach to the printed circuit, and I plug everything back together like I have multiple times before and the right side of the gauge cluster just doesn't come on when power is turned on. This is the voltage meter, fuel gauge, h20 temp, and oil pressure gauge. All inoperable in the span of 15 minutes with nothing done to them.

The rest of the gauge cluster/meter is getting power. By this I mean the signal indicators, brights indicator, 4wd indicator, backlights, parking brake indicator, and tach (its getting power- not working though).

Here's what I've done to try and chase it down:

1. Check/replace all fuses. Inside and the 3 in the engine bay. I got a fuse checker for this.
2. Check/undo/sand/retighten the grounding point right above the interior fuse box. I believe the two grounds from the gauge cluster terminate here.
3. Check the printed circuit itself. There is a small portion that looks like it goes to a bulb that seems a bit damaged, but that looks like just the blue plastic and not the metal circuit itself. I put a small piece of electrical tape over it.
4. Lightly sand (220 grit) and apply dilelectric grease to the points where the plugs enter the meter.
5. Taken apart the meter itself and checked the gauges for visible damage/burns. Nothing noted. Put back together as before.
6. Disconnect negative terminal on the downstream battery and reconnect a couple minutes later.
7. I have removed the three small screws that tie the tach into the gauge cluster circuit to see if that would bypass the problem.

None of these things have worked. I had zero problems with this part of the gauge cluster.

I'm at my wits end. Its like the whole thing worked and then it just didn't.

Any ideas? Thanks in advance

 

[JuanJ]

Hello,

You have already addressed two of the most common causes, i. e., fuse and ground.

There is an electrical continuity loss somewhere.

You have to check for continuity system by system: tachometer, oil pressure, voltage, parking brake... The procedures for each varies but, generally speaking, involves a meter, a testing light and a voltage source: disconnect the sender, check continuity, repeat.

The FSM is your friend here.

Hope this helps.





Juan

 

[badusmaximus]

Thanks for the response @JuanJ. You're correct about the FSM. Sat down tonight with a drink and wrote out all the connections vis a vis the FSM.

Went through and checked om continuity on all the affected circuits on the plugs- harness side and on the meter itself.

I'm sort of new to this, I did the OM test with the sound function and ignition off. Would it be better to do it with ignition on and just read the amperage?

Since all the gauges on this circuit run off the ENGINE fuse, I checked continuity at the fuse joints. No problem there. Brand new 15A fuse in there as well.

I found that on harness, I wasn't getting a connection on the A7 -> B8, A7 -> A4, and A7 -> A6 pins.

On the meter, I didn't get a connection on A7 -> B5, A7 ->B6, A7 -> B8, A7 -> A4, A7 -> A6, or A7 -> B2. Granted I did disconnect the tach before this test, so the last two tests are possibly irrelevant.

I think that all the jostling in and out may have loosened the connectors on the harness side. I'm going to pull the wires tomorrow from the plug and refresh them.

What doesn't make sense to me is that the meter would just fry like that- I didn't drop it or do anything really besides remove/inspect the tachometer. I'm buying a used meter assembly to replace the faulty tach- I will likely salvage what else I can. Might need to buy a new printed circuit board?

What I'm really wondering is- are there any common failure points in this area that people are aware of?

 

[jblueridge]

My oil pressure gauge and fuel dropped out at the same time once.
I got into the dash and carefully examined the flexible printed circuit.
Nothing to see. Other tests showed gauges were not at fault.
Reassembled and found things worked again.
I never found out what was wrong or how it was fixed.

 

[badusmaximus]

@jblueridge that sounds eerily similar to how mine just... stopped. I'm going to continue testing. I'm not noticing any damage to the wires themselves but I'm unsure of where the grounding point for this circuit is. I believe it's a common ground point, listed "c" on the wiring diagram. That points it to under the left pillar. I think that's in a similar place as the right side.

I should probably disconnect and reconnect the senders with dielectric grease. I'm having a really hard time believing all 4 senders just failed at once- unless there was some weird surge that took em out.

 

[JuanJ]

Thanks for the response @JuanJ. You're correct about the FSM. Sat down tonight with a drink and wrote out all the connections vis a vis the FSM.

Went through and checked om continuity on all the affected circuits on the plugs- harness side and on the meter itself.

I'm sort of new to this, I did the OM test with the sound function and ignition off. Would it be better to do it with ignition on and just read the amperage?

Since all the gauges on this circuit run off the ENGINE fuse, I checked continuity at the fuse joints. No problem there. Brand new 15A fuse in there as well.

I found that on harness, I wasn't getting a connection on the A7 -> B8, A7 -> A4, and A7 -> A6 pins.

On the meter, I didn't get a connection on A7 -> B5, A7 ->B6, A7 -> B8, A7 -> A4, A7 -> A6, or A7 -> B2. Granted I did disconnect the tach before this test, so the last two tests are possibly irrelevant.

I think that all the jostling in and out may have loosened the connectors on the harness side. I'm going to pull the wires tomorrow from the plug and refresh them.

What doesn't make sense to me is that the meter would just fry like that- I didn't drop it or do anything really besides remove/inspect the tachometer. I'm buying a used meter assembly to replace the faulty tach- I will likely salvage what else I can. Might need to buy a new printed circuit board?

What I'm really wondering is- are there any common failure points in this area that people are aware of?

Hello,

Some tests require ignition on, some do not. Amperage by itself does not tell you much. Think of it as a pipe circuit: if you have a leak, you still have flow through the system. If you isolate sections and pressure test them, you can spot the leak and fix it.

A peeled wire in the harness can cause a ground that shuts the whole circuit down. Aside from visual inspection, electrical continuity tests help to find on of these.

Unless someone (like a PO) does something really stupid, electrical systems disconnect themselves before the damage extends, because they have safety features intended to do that. It is possible the printed circuit is still functioning. However, if it is in fact damaged, you may need to get the whole assembly.







Juan

 

[badusmaximus]

@JuanJ have you had to dive into this part of the harness at all?

I opened up the split loom today between the plugs and where the wires meet the rest of the main cabin harness. I found a naked metal segment that spliced into the grounds coming from both the A and the B connector. It wasn't threaded like a wire, it was almost like a hollow mesh. Everything around it was insulated, and it was all wrapped in tape and the split loom stuff itself. I think its a way to distribute the ground load between the two plugs on the circuit. Factory? I'm not sure- no mention in the FSM diagram.

How do you access the main cabin harness there? If I have rogue connections or damaged wires, I haven't found them yet. My only other theory is that the connections between the plug and the printed circuit are worn.

 

[JuanJ]

Hello,

I had to dive in the combination switch harness and the ignition switch harness. The former because one day I lost high beam lights, the latter because of non-factory wiring I removed, which caused the electrical system to go off. I checked the instrument panel on both occasions, although not as thoroughly as you did.

I do not remember seeing the metal segment you mention in the instrument panel. There is, however, a mesh cable (not sure if it is the right description) that makes a ground connection to the frame in the transfer case, an entirely different environment.

Regarding rogue wires, they only chafe/peel when exposed. If your harness still has its outer wrapping intact, chances are the wires inside are in good condition. This leads to the connections, which may be worn or dirty.

I found a picture of my printed circuit. No metal segment. Notice that it is 12V.

Juan

 

[badusmaximus]

Here is a picture of my PCB. The naked wire I was referring to was in the harness bundle itself between the PCB plugs and where it joins the rest of the dash harness.

Apart from a small burn in the blue plastic kind of above where the yellow wire does that 90* turn, I don't see any visible damage. No visible damage to the gauges themselves, however I did the FSM test for oms on the gauges themselves and was not getting proper readings there. I think the reading I was supposed to get was like 55 amps.

I noticed that I bought the truck with a 10A fuse in the Charge port instead of the 7.5A that should have been there. Would that extra 2.5A have been enough to fry my gauges? I changed it after I this problem materialized.

Also please excuse my dirty seat- due for a shampooing!

 

[JuanJ]

Hello,

No, I did not have naked wires in my harness. Creative grounding from the PO, I presume. The cable and the 10A fuse make me think that is the case. 2A is enough to power a home appliance; it is certainly too much for any circuit.

I remember the FSM advised to check the connectors for dirt or damage. Yours look a bit worn. As per FSM recommendation, it is worth applying conductive paint with a marker after cleaning.

Last but not least, no worries about the seat. A good excuse for a thorough cleaning...




Juan

 

[badusmaximus]

Bumping this to see if anybody has any insight.

I ended up getting a replacement Tach from a mud member which is installed and working.

Also ordered replacement fuel/h20 and oil/volt gauges from @SteveJackson at Cruisers Direct. I popped them into the cluster and nothing. Not even a signal through the voltmeter which causes me to believe I have a lack of continuity within the gauge cluster itself (printed circuit board? There was a small burn spot but I sanded it down, patched with foil tape, and insulated with electrical tape).

Everything else on the circuit that feeds these gauges works. Per FSM: plug A7 also provides power to the tach, brake warning light, and 4wd indicator light. These all work. No damage on plugs or on harness in dash.

There is a chance that the grounds for the gauges (aka the senders) all failed simultaneously due to power surge- but then why wouldn't the voltmeter pick up any signal? This shares a common ground with the Tachometer which is replaced and working (B2). I have a new oil sender I'm going to install this week to test this theory.

I think that I have some non-visible damage to my printed circuit that is causing me to not get power to the gauges. Thoughts?