Instrument Panel Issue

[george barringer]

1978 Ericson late model A4

This is a work in progress - bringing an abused boat back from the brink. Triage is the operative word. Fix everything or fix the basics and go sailing and work away at the ever lengthening list.

During the past layup

Was having continued problems with the engine installation.

Did the usual tune up.

Fixed fuel issues by replacing fuel lines, filters, cleaning carburetor, and tank which was badly corroded. A new plastic tank installed. This required some re-arrangement and a new fuel filler line and a rerouted ground wire (terminating at the same point) and fuel gauge wire.

On to the instrument panel. Standard and original 5 gauge Ericson panel. I've been running with a partial panel for a few years - ammeter, oil, temperature - all worked correctly. No fuel gauge (sender corroded byond identity when I got it out.) No tach.

Now. Everything back in place. But - all gauges pinned at high end with 12V on - engine running or not. Lifting the lead to one of the gauges brings it back (but not the rest) back to zero.

I think I have lost the panel ground or grounding through the defective tach. Any ideas?

Thanks

George Barringer

[JOHN COOKSON]

Originally Posted by george barringer

But - all gauges pinned at high end with 12V on - engine running or not. Lifting the lead to one of the gauges brings it back (but not the rest) back to zero.
I think I have lost the panel ground or grounding through the defective tach. Any ideas?
George Barringer

Remove the wire from the sending unit at the gauge and turn on the power. The gauge should peg low scale. Then short the gauge sending termminal to ground. The gauge should peg full scale.
It sounds to me like your sending unit circuts are grounded somehow. To confirm run a jumper wire from battery ground and test each one to ground at the gauge end with an ohm meter.
Exactly which wire are you lifting them makes them work? The one from the sending unit? Doing this probably interrupts the short to ground.

TRUE GRIT

[Sony2000]

I like it when you speak of isolating a gauge. and testing it. I'll be able to lye in my captains bunk, looking at all that spaghettii, with your printout in hand, and knowing, I may find the source problem.

[george barringer]

Yes - disconnected any gauge - oil, temp, or fuel at its sensor end and it goes low - as I expected.

The real question is - any idea on what single failure causes all 3 to go high? The ammeter is isolated from the rest and is working. There's clearly a single common ground path somewhere tieing all the gauges together.

I guess I'll ope it up this weekend.

Thanks

George.

[JOHN COOKSON]

Originally Posted by Sony2000

I like it when you speak of isolating a gauge. and testing it. I'll be able to lye in my captains bunk, looking at all that spaghettii, with your printout in hand, and knowing, I may find the source problem.

If you get stuck or need encouragement put up a post. I and several others in the forum have been around the block with gauges and wiring.

I will say one thing: Rewiring the engine, gauges, and the rest or the boat is probably the one best thing I ever did on the boat in 30+ years of ownership.

TRUE GRIT

[Sony2000]

On my project boat everything is being supplied by two batteries, and I'll add the alternator next season. I know what each fuse supplies current to, and I added a busbar for all the ground wires lying around. The weird signals I'm getting are:
1. When the key was turned to start, the oil pressure guage went from 100psi to 0 like an ammeter. Corrective action was to hot wire from the second post on the key, to a starter button and move the starter wire to the push button. I don't know if it was a wise move, but at least I feel better.
2. If I knew where to put the large and small wire for the nonexistant alternator, I maybe able to have the ammeter come alive.
3 Water temperature guage goes to 160 with the key on.
Now that the engine is running better, its ready for its 3rd sea trial. The mechanical oil pressure guage is normal at 40 psi, and the engine block is kept cool with large shoe and no thermostat.
I'm trying to get the guages to mimic reaity.
Any thoughts may lead to a better indication on the SS Minnow.

[ndutton]

Sony, an accurate drawing of your wiring would really help. It doesn't have to be pretty, hand drawn is fine.

George, it's clear to me the 'S' terminal on all three gauges is somehow grounded which it should not be. I doubt all three would suffer damaged sender wires at the same time which leaves miswiring. Be sure the three gauges have no ground to them (other than the illumination lamp). Ignition and individual sender wires are all they get. In fact, until this issue is solved I'd get rid of the illumination wiring to make troubleshooting easier. That would leave 2 wires per gauge, 'I' (ignition) and 'S' (sender).

[Al Schober]

No Neil,
The gauges need 3 connections - 12V hot, Ground, and sender. If all gauges are acting strange, I'd suspect the common connections - either power or ground.

Al

[ndutton]

Sorry Al but I gotta disagree. For the three gauges mentioned the only ground is via a variable resistance sender. Please see the attached Moyer diagram. No grounds to the oil pressure or water temp gauges. The fuel gauge, not pictured, works the same way.

Gauge illumination is another matter, not part of the gauge function and does require a ground but it's only for the light bulb.

[Sony2000]

Key on, temp 160. @ !0 o'clock. Oil 80 psi @ 2 o'clock, ammeter @ 6 o'clock.
Push button starter was added by me. Pink wire from key # 2 to new button. #3 wire moved to button.
Running, the oil shows 20 psi on the electric gauge, and 40 psi in the mechanical one. Temp stays the same as does the ammeter. (no alternator)
PO removed the connection for the instrument lights.
Alt. red wire seems to go to + on ammeter.

[ndutton]

If the large red wire goes to the alt as you say the color coding can't be trusted. If it were correct, the orange wire would be the alternator output, the red one should go to the battery.

One thing at a time though. Dealing with the oil pressure gauge only, I'm trying to follow the blue sender wire. It loops under the floating circuit breaker and disappears. Can you tell me where it goes?

[JOHN COOKSON]

.......But it's easy to check.
It the sending unit for temp wired to the oil pressure gauge and the sending unit for the oil perssure wired to the temp meter?
When a PO is involved anything is possible!!!!!!!!

TRUE GRIT

[Sony2000]

Ndutton, the surveyor made the comment, not to trust the color codes. The navy colored wire goes to the harness connector and switches to a royal blue wire that goes directly to the oil pressure sensor.
The beige sender wire from the temp gauge goes into the harness connection and exits beige as well, and over to the cylinder head.

[george barringer]

All:

Thanks very much for all the input. It insured I was working in the right direction.

Did some independent research. Gauge schematics from suppliers show connections to +12, sensor, and a separate ground.

Last weekend opened the panel - I couldn't find the anticipated separate ground so I stripped the panel down to bare essentials no illumination. Just +12v to each gauge and the sensor wire to the appropriate sensor. The gauges still reading incorrectly as I suspected. Added a separate ground wire to gauge(s) back to engine block - all is well. The fuel gauge is still disconnected for the moment while I gufure out if it has the right resistance for the sender.

So - it appears that the instrument panel was grounding through the original aluminum fuel tank to engine (earth) ground. This ground path was broken when the tank was replaced with a polyethylene replacement - which has the required grounds to the fuel filler and on to the system common ground - which is also grounded to the engine block. All I can think is that the fuel gauge was acting as a ground path through the sensor which was connected to a highly defective sensor in the original Al tank.

Gauges need 3 good connections - +12, sensor, and a good ground.

So - problem solved on this score. Thanks everyone. Now will try to fix steering cable which chose this moment to go south.

[ndutton]

George,
What brand and model gauges do you have?