ea81 Electrical, ig coil/fuel gauge fuse blowing

[ferox]

Well my beloved '81 hatch has developed a troubling issue. The gauges and fuel pump are not receiving power. The [ig coil/fuel pump] fuse blew and continued to blow upon replacement. My first suspect was the FPCU so I jumpered my fuel pump to 12v and it pumped great. Next I bypassed the FPCU and the pump will run for a second before the fuse goes again, so I don't think it's the FPCU.

 

The fuse element melts fast and hot, so I am done with the powered troubleshooting and diagnosis. I am getting ready to pull the instrument cluster and maybe the steering column for access, so I thought I would check in before I do so.

 

I am wondering if anyone has any ideas on something specific I should look for, something common to the gauges and fuel pump perhaps. Ignition switch? Ground(s)?

 

Many of the lights in the dash light up like open-door lights and such, just not the gauges and clock. The seatbelt chime works also. I checked the coil and it's fine. I switched to an internally regulated charging system years ago with no problems so the external VR is not an component.

[GeneralDisorder]

Do you have a diagram that shows *exactly* what is hooked to that fuse? You can should hook a meter to between load side of the fuse connection and ground then disconnect all the things powered off that fuse one at a time till the resistance jumps up.

 

GD

[ferox]

Do you have a diagram that shows *exactly* what is hooked to that fuse?

 

Yes I managed a decent scan of my FSM wiring diagram. I'm working on tracing connections.

 

You can should hook a meter to between load side of the fuse connection and ground then disconnect all the things powered off that fuse one at a time till the resistance jumps up.

 

Thanks, it's probably going to take a while, but at least it's systematic. To be clear, do you mean disconnect things one at a time, check meter for resistance, then plug that thing back in and move to the next item? The idea being that there is a short somewhere allowing too much current to pass through the fuse, correct?

[GeneralDisorder]

Right. Current = voltage / resistance. You know the voltage, and you can test the resistance. If you dont have a resistance that yields a current small enough to fit the fuse in the hole.... You have a short or some device drawing too much current. Find the device or the short and your resistance will jump to an acceptable level.

 

GD

[ferox]

Cool thanks, I'll report back on what I find.

[ferox]

It "seems" that my instrument cluster contains the problem. When I unplugged the main harness connector to the cluster the resistance jumped up. When I unplugged the pin-connectors they each made the resistance jump up by approximately 1/3 of what the main harness disconnect indicated, so that did not really narrow down the possibilities. Diodes checked out ok, and the VR does not have any continuity.

 

One thing that comes to mind is that the brown slime that I find on a lot of these ea81 dash connectors was prevalent between the circuit board and cluster (see photos). What is this stuff? I have always assumed it's the old style of dielectric grease that was brown. Is this stuff conductive?

 

 

 

Everything else looks great except the fuel gauge. On the bottom of the gauge there appears to be a bi-metallic switch that I am guessing is for the low fuel light. One end of the wire wrap is frayed and I can't see the other one. It seems to be coated in the brown slime and slightly cooked. Obviously that is not a good sign, but I also don't get any continuity through it, so it does not seem to indicate that it is the problem just a problem.

 

 

 

 

 

Also found out that the gauge face paint does not like isopropyl alcohol.

 

 

 

 

I think I know the answer to this, but will an '82 fuel/temp gauge work for an '81 or am I limited to '80-'81?