When you back-probe, you push a pin into the back of the wire of the electrical connector. You make sure the pin you pushed in has continuity to the pin in the electrical connector. That way you can plug in the electrical connector and do tests on it.

Does that make sense?

 

Ah yes, Do that all the time. Have a special set of meter leads for it.

Where can i start testing to track down this fault?

I'm thinking by starting tracing the power feeds to and from the gauges again but i just cant seam to find where they all converge......

And why it would be drawing power from the lighting and not the ignition........

 

I would check for a voltage drop between the white wire going to the ignition switch to the yell wire going to the gauge cluster. It is pin C3 (see attached pic). The key will have to be in the II position.

This would check a problem with the ignition switch.

Also verify that the yellow wire at C3 has 12V when the key is in the II position.

 

Testing today, Ill post the results.
Thank you for the img / pinnout.

 

Ran the tests.

1. White wire on the ignition with the key in the II position measured 12.54vdc
2. Pin C3 Yellow wire with the key in the II position resumed 12.52vdc.
3. Remeasured the White wire on the ignition and measured 12.53vdc.
4. Calculated a voltage drop of .01vdc

Ran a few further checks.

1.Turned key off and removed.
2.Turned on headlights.
3.Measured 12.50vdc at the white wire on the ignition switch.
4.Measured 12.49vdc at pin c3.

Also I decided to check the yellow wire at the connector on the right hand side of the gauge as viewed from the front. I am assuming this is a power wire just the same as in the other connectors. That is what my diagram says.

1.With the key in the ii position i read 0vdc.
2.With the headlights on i measure 0vdc.

I tried jumpiness 12vdc from the yellow wire on the ignition switch to that yellow wire with the key in the ii position. Still no gauge function. It was just a momentary "tap" of a connection just to check.
I also discovered that the two far right pins on that connector have 12vdc at all times regardless of key position.
I also ran a ground check for all three connectors. All have good grounds on their respective pins.

At this point I suspected the cluster it self so i swapped in another identical cluster from my other honda to check. Nether cluster will power up with the key in the II position, but both power up with the headlights/marker lams on regardless of ignition switch position.

 

Was there voltage on C3 with the ignition switch off and the headlights off?

 

No there was not. With the ignition off and the headlights of, C3 had no power.

 

This has to be a ground problem. I guess my next test would be on every black wire on the electrical connector for the gauge cluster and the headlight switch. I would back-probe the electrical connection and do a voltage drop to a known good ground.

Maybe try unplugging the headlight switch and see if the cluster works?

This is a strange problem.

In that shop manual I referenced before, the grounds locations start on page 23-16. You may want to find and clean all of them. I would also clean where the negative battery cable grounds to the radiator support and the engine block.

 

Already tried unplugging the headlight switch. Gauges do not function.

I will Proceed to check all the grounds referenced in the manual (thanks by the way for the much more detailed schematics and manual)

Ill update my results tomorrow.

Your help is and has been much appreciated solving this problem.
At least i have gauges when the running lights / headlights are on ;-).

 

Finally at last SOLVED!

Turns out the Integrated control unit had shorted as well as the instrument cluster.
I Opened both units and found burnt traces on the boards. When these traces blew they lifted up and touched other traces, welding them self's in place and bridging circuits. I Tracked the origin of the short to two frayed wires that had touched. I repaired the traces on the boards seeing as they were designed as "fuses". You will notices these traces on circuit boards seeing as they go from a "fat" trace to a "half width" trace for a very short length in the middle of a straight trace. Think of them as built in slow blow fuses. All is now in working order with the original parts.
Ya i know, it would have been easier to replace the two parts but i design electronics for a hobby and couldn't resist repairing em.