78 Gauge Cluster/ Electrical Issues

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T

TN78FJ40

10 Year 15 Year
Joined
Jan 10, 2009
Threads
7
Messages
26
Location
Goodlettsville, TN
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?
 
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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.
 
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.
 
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.
 
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.
 
pb4ugo said:
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.
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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?
 
CruiserInProgress said:
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.
Click to expand...
Which 3 lug terminal are you referring to?

20261003_073544.webp
 
Engineer8000 said:
See if you have pulsing 7V on the center terminal of the fuel gauge.
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I do not have any pulsing voltage on fuel gauge terminal.

I do have a full 12v to the oil terminal. It looks like someone ran a jumper wire to the fuse box for just the oil wire. I thought I had read that it should only be about half the voltage going to gauges??
 
The oil gauge is 12v, the fuel gauge has an internal regulator making about 7v for it and the temp gauge. The pre 73 clusters had different senders for fuel and temp.
 
Has the plug ever been depinned? Is there any chance that the terminals aren’t properly seated or in the wrong position?

It would be odd for all 3 gauges and temp to fail. The blue/ red wire from the fuse panel only powers the fuel, oil, and temp. Lights come from the headlight switch, and ammeter is reading from alternator and battery.

calsum2

Post in thread 'Temperature sending wire'

barrel connector lay out mirrored.webp
barrel connector lay out mirrored.webp
 
TN78FJ40 said:
I was able to ohm out the wires from each sender/sensor back to the 12 pin connector. So if I have 12v to the cluster pin, the ground in the cluster pin is grounded and know that wires are intact to the units, what do I check next?
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When I had trouble with my fuel and oil gauges I ended up cleaning and soldering the crimped pins of the plug to the actual circuit board. They had high resistance connections.
 
Making a little progress. After wire brushing connections and make straightening the pins/barrel connector, I was able to get the temp work. Oil needle moved a little so I will start diagnosing if I truly have that low of oil pressure. Can I screw a gauge straight into to oil sending unit just to check pressure(Amazon has pressure gauge with 1/8 bspt threads)?

Still no movement on Fuel Gauge, but I'm making progress thanks to your help!!
 
Grounded out wire to oil sending unit and the needle went all the way to the right. Removed oil sending unit and put a pressure gauge into the orifice and it was reading 55 PSI at idle. Cleaned all connections and reassembled, needle still reading very low pressure. What do I need to change or check next?
 
Back about 85 I got sick of the crude gauges on my tractor. The oil pressure gauge was erratic at best - I tried almost everything, and nothing solved the issue until I gave up and bought a direct read lighted gauge. I made a bracket to hold the gauge above the steering column. I ran the plastic oil tube inside some fuel hose from the back of the gauge to the engine side of the fire wall, that way if the tube broke I would not get a face full of hot oil. I also put a pipe plug in the ash tray to block off the engine port in the event of tubing failure. Everything is still there and working fine.

Was really nice to have an accurate gauge when I swapped out the distributor - I didn't get the dizzy pressed down far enough the first time due to a fat o-ring. I had the plugs out and was just spinning the engine over with the starter - no oil pressure built in a short time, so I knew something was wrong.
 
TN78FJ40 said:
Grounded out wire to oil sending unit and the needle went all the way to the right. Removed oil sending unit and put a pressure gauge into the orifice and it was reading 55 PSI at idle. Cleaned all connections and reassembled, needle still reading very low pressure. What do I need to change or check next?
Click to expand...

You l likely need a new sender. The guage appears to be working.
 
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