Hi Stan --

After fleshing out the current flow for the 1989 volt gauge, looking at the 1985 diagram shows that the path goes through fuse 10 and connection CE J14 and on through pin 5 of the instrument cluster C connector in black/red livery. Test at J14 for full voltage. If low, look at fuse 10 and the CE panel connections under that fuse. If you see full voltage, check at the instrument cluster connector pin 5 in that C connector. If you see full voltage there, clean the card edge contacts for C. Still a low reading? Clean MP-IV ground point.

CE panel J14 goes to a distribution point labeled "VS V" in the wiring diagrams. I don't have first-hand experience with what that actually looks like, but if you see full voltage at CE J14 but not at the harness side of cluster C5, find that distribution point and clean.tighten it.

Fuse 10 gets power from the 15 bus in the CE panel, supplied with battery voltage when the ignition switch is in the Run (2) or Start (3) positions. If the fuse itself shows less than battery voltage on both sides, measured in circuit engine running using a needle probe into the test ports on the fuse itself, look hard at the circuit from the ignition switch at CE connections B11 and B12. If they show low, look hard at CE connections A11 and A12, which supply power to the ignition switch. If full voltage at A11 and A12 but low at B11 and B12, it may be the ignition switch itself. Clean/verify the CE A and B connectors, and the plug at the ignition switch itself.


For those playing along at home, the terminal numbers and descriptions discussed here are based on a look at the MY 1985 wiring diagrams in the WSM. They may not apply to your car, so be sure to build your own diagnostic protocol and description based on your own MY drawings.

 

Dr Bob thanks for taking the time to research this and type it out ,
I do appreciate your effort and will be heading to open up the CE panel and do more testing

 

This is turning into an interesting subject. Folks need to know that Stan knows this stuff a lot bettter than I do, so the discussion is here so that others can play along when thy have similar symptoms. Might be a worthwhile task to make a more universal discussion with the details for each generation.

Me.... I watch the gauge to make sure it stays above 12. I'd need to plug a meter into a few placees to see how accurate the gauge reading really is. Like the temp gauge, I watch for changes from what it usually reads, rather than looking for some perfect absolute reading. Saw that my temp gauge is sitting two needle-widths below the 190 degree line, and the heater works well on a cool morning. Seems fine.

Lots of fun stuff!

 

To be sure,
I learn something new everyday
Your wire diagram reading and interpretation is really excellent.

 

I’ve noted the same bouncing volt gauge behavior in my 88.

the bouncing happens sometimes not always. The above video was taken while driving with rear def, hvac fan on high, and rear fan on high. I’ve previously calibrated my gauge to the voltage at the CE and my front engine harness and alternator are new. And I cleaned MP IV within 4 months. I also verified all the connections in my 14-pin connector.

the bouncing seems to be a very common problem through many years. It’s a very curious problem.

. I have Led bulbs in those warning lights, so I wonder if there is some interaction problem with the LEDs.

 

a

Thats a cruise oil pressure?

 

Mike, on your 1988 car...

Similar to the 1985 description for Stan's car: The power for instruments comes from the 15 contacts in the ignition switch, through fuse 10, out of the CE panel at J14 (black with red tracer) to a junction labeled "5" on the drawings, continues black-with-red-tracer to connection at the cluster connector C terminal 5. Since it looks like a lot of your gauges might be reading a little low, I'd start by replacing fuse 10 or at least slide it in and out a few times, plus some Deoxit. Then check voltage at CE panel J14 to see that it matches the CE 30 bus voltage at the top, and the dash voltmeter reading. Clean those red power inputs especially the two KS1 feeds from the jump post if the CE panel end reads lower than the jump post readings.

Turns out that fuse 10 is responsible for a lot of things, like exciting the alternator, power for dash indicators (bulbs) as well as power for the gauges. A little bit of corrosion in the fuse connections can affect a lot of seemingly unrelated readings.


Once again: The terminal numbers and fuse designations listed are from the 1988 wiring diagrams. Check the diagrams for your car if it isn't a 1988 model, and there's a good chance that things might be different.

 

Which gauges are you seeing reading low? What should they be reading? Are you referring to my oil pressure? What should it read when cruising at 2500-3000 rpm with fully warm oil?

I'll make sure i double check Fuse 10. Thanks for the suggestions as always. ;-)

 

2500 Cruise on the hottest day has the oil pressure gauge pegged on my car. It's there from well below 2000 RPM actually. Do you see yours pegged on cold start? If not, you might want to look a little harder at that reading.

Your wire diagrams show how the same feed from fuse 10 powers pretty much every indicator in the cluster. Wicky readings anywhere in the system deserve a fuse 10 cleaning and reseating I think.

I guess I need to go do this on my car too. No odd readings so far, but it's simple and easy to clean any oxidation now before it gets thick enough to noticeably affect readings.

 

Well Ill be derrned,
First thing i did was install a new cig lighter voltage monitor ,
I took it for a ride,
the voltage was staying at 13.5 or better for most of the trip but it was steady,
the gauge was jumping around like a jumping bean.
So I took the old #10 fuse out and put a new fuse back in. started it and now its steady as a rock. Perfect
Thanks for all the help