78 Gauge Cluster/ Electrical Issues

[TN78FJ40]

Cruiser has been sitting for about 5 years. Recently got it running and only the Volt meter is working in cluster. Lights work in cluster. I went through wiring diagram from Coolermans site, pulled the cluster and disconnected the plug. I am getting 12v from blue/red stripe wire using ground in plug. But I am not getting any voltage from gas/ temp/oil. Should I be able to read volts at the plug for all three?

Any other diagnosis tips I should try?

 

[charliemeyer007]

On my 72 the ammeter (30A) supplies like 5V to power the other instruments. You should carefully inspect and clean all the contacts after removing the battery ground cable.

 

[nabbasi]

You shouldn’t necessarily read voltage for the sensors.
You say you have 12V+ from the LR - which is the 12V+ for the cluster.

You said voltmeter - but is it actually an ammeter?

I’d start with checking continuity between the sensors and cluster. You’ll want continuity between the oil pressure gauge and oil pressure sensor, coolant temp sensor and temp garage, etc. Alligator clips or spade connectors on some extra gxl wire are helpful to extend your wires.

 

[pb4ugo]

Disconnect battery, pull all the fuses and use a 22 caliber wire brush and clean the contacts in the fuse box.

Pull the wire leads on the senders, with key on, ground them for a little bit and see if the gauges move. Most importantly, Be sure to disconnect the battery b4 you remove the cluster. You can easily fry the harness.

 

[CruiserInProgress]

About the oem 79 50A ammeter. It indicates current, but is actually a voltmeter that reads voltage across your fusible link (between battery and alternator). And yes, disconnect battery when removing or installing cluster. Very easy to make contact with the metal dash.

I had similar problems with my 79 cluster and discovered several tarnished contacts, not just in the large multi-pin connection, but also in the three lug terminal. There, I also discovered the rivets holding down the three lugs to the cluster's copper circuit weren't making contact and required soldering to make a proper connection.

Not sure where your issue lies, but don't trust those aging connections or copper circuit that's part of the cluster.

Glad to hear you're using Coolerman's color-coded schematics. They helped me a great deal in sorting out my cobbled wiring.

 

[TN78FJ40]

Disconnect battery, pull all the fuses and use a 22 caliber wire brush and clean the contacts in the fuse box.

Pull the wire leads on the senders, with key on, ground them for a little bit and see if the gauges move. Most importantly, Be sure to disconnect the battery b4 you remove the cluster. You can easily fry the harness.

I did clean the fuse panel with wire brush a couple of weeks ago. It did solve my lights not working issue. I assume since I have power to cluster plug, there is power coming from fuse panel?

 

[TN78FJ40]

About the oem 79 50A ammeter. It indicates current, but is actually a voltmeter that reads voltage across your fusible link (between battery and alternator). And yes, disconnect battery when removing or installing cluster. Very easy to make contact with the metal dash.

I had similar problems with my 79 cluster and discovered several tarnished contacts, not just in the large multi-pin connection, but also in the three lug terminal. There, I also discovered the rivets holding down the three lugs to the cluster's copper circuit weren't making contact and required soldering to make a proper connection.

Not sure where your issue lies, but don't trust those aging connections or copper circuit that's part of the cluster.

Glad to hear you're using Coolerman's color-coded schematics. They helped me a great deal in sorting out my cobbled wiring.

Which 3 lug terminal are you referring to?

 

[CruiserInProgress]

Which 3 lug terminal are you referring to?

View attachment 4223585

That looks like the older 30A, direct feed (two heavy wires?) ammeter cluster. The US 79 oem 50A cluster has a 3-pin connector mounted to the circuit board instead.

 

[TN78FJ40]

That looks like the older 30A, direct feed (two heavy wires?) ammeter cluster. The US 79 oem 50A cluster has a 3-pin connector mounted to the circuit board instead.

I just realized I put 79 cluster in title.. It is a 78

 

[Engineer8000]

See if you have pulsing 7V on the center terminal of the fuel gauge.