Instruments not working

[Will S]

Hello,

I am the new owner of a 1975 pearson 28-1. I'm pretty inexperienced when it comes to engines, but am doing my best to learn what's going on down there.

For the most part, the A4 putters along alright. I'll start another thread for the issues the engine itself is having.

The engine is equipped with an ammeter, tachometer, oil pressure gauge, and water temp gauge. The ammeter is the only instrument which does anything. Do you all have any troubleshooting suggestions to track down what's going on?

[dvd]

Will

Depending on the age of the gauges you might just start replacing them, along with the various sending units. Moyer sells all the gauges you said weren't working. Trying to get old gauges to work may be more trouble than they are worth. You may just start by following the wires from the back of the guage to their various points where they go. The temp guage will go to a sending unit that should be up front near the T-stat. Make sure its hooked up properly. If you replace the sending unit you are supposed to replace the guage as well.

dvd

[JOHN COOKSON]

Welcome to the forum.
Hang in there; I'm working on a reply as I find time.
Others may beat me to it. That's OK.

TRUE GRIT

[Dave Neptune]

Lotsa plugs!

Will, first welcome to the Afourian MMI Forum!

The first thing to check is the wiring harness connector. Most A-4's were shipped with a big "trailer plug" to connect the engine to the panel. Those often start back up with a wiggle.

After that check the grounds on everything including the block to battery.

Look for corrosion and if found clean toss some dielectric grease on it and look for another.

Dave Neptune

[sastanley]

its just a bunch of wires! Check every one!

The +12v power for the gauges should come from a purple wire...these are often daisy chained in the back across all the gauges..therefore if one up the line loses +12v, so do the others down the chain. this is also true for light power & ground, generally. The sending units each have their own dedicated wire between gauge and sending unit.

I just rebuilt my entire gauge panel 2 seasons ago, and just the other day noticed I had an intermittent ground on my oil pressure, so it happens to everyone. If you think about it, there are usually at least 3 or 4 connections on each gauge..+12v, ground, sender, & another +12v for the light. Lotsa stuff to quit working on a tiny gauge.

Dave Neptune's approach is a good place to start..check the big obvious stuff, then move to each gauge individually. I'd start at the back of the gauge panel with the appropriate small wrench and make sure all connections are snug. Then, get a simple volt meter back there and start checking. Ground should be black & positive should be purple (& the purple likely coming from the ignition key...i.e. when the key is on, the gauges are powered) - let's see what you got.

Brown/Tan is usually the sender for the water temp, oil is blue/light blue. Make sure those are snug on each end (at the gauge & motor) to be sure the sender can get its signal back to the gauge. The temp sending unit (late model) is usually right next to the oil fill, and the oil sender is usually to the left forward of the motor between the carb & flywheel.

Incidentally, the ammeter likely has its own dedicated wires from the charging circuit and is completely independent from the rest of the gauges (which is why it works)..the only common aspect being that it is bolted into the same cluster..that being said, I also seem to recall my buddy Ajax's Pearson 30 doesn't have all the gauges in one cluster either.

Check these easy things first, & we'll go from there.

Oh,and welcome!

[Will S]

Thanks for the ideas! I'll see what I can find next time I get out to the mooring.

[JOHN COOKSON]

In the typical wiring scheme each gauge will have three wires going to it: A red hot wire, a black ground wire, and a colored wire from the sending unit on the engine connected to the middle terminal. The gauges are supplied with electricity when the key or switch is in the on position.

To get started on the troubleshooting turn the key or switch to the on position* and measure the voltage at the hot (red) lead on the back of each gauge. If you stare at the wiring long enough you can usually see how all this is wired together. Once you have electricity to each gauge report back if they still don't work and I'll tell you what to do next. My guess is that with all the gauges out you don't have power to any of them.

You might consuly the "drawings and schematics section of the forum to get an idea how the gauges are wired.

*CAUTIONisconnect the wire from the key or switch to the coil before leaving the power on for more than a minute or two when the engine isn't running and the points or EI is closed or the coil will be fried.

Welcome aboard. We're glad you're here.

TRUE GRIT

[Will S]

I had a short bit of time to check a few things. I cleaned all the contacts on the water temp gauge and it works now.

Things look quite different from all the diagrams I've seen, I guess things must have been rewired.

Sorry for the fuzzy picture... Here's the upper part of the panel. The ammeter is to the right with all the orange wires. The temperature gauge is to the left. Any idea why there are so many wires on many of the terminals?


The oil gauge is a bit puzzling. There is a unit on the engine that the hot wire for the fuel pump goes through. I guess this is an automatic fuel shutoff in case of low oil pressure? There is a copper tube leading out from the base of that assembly to a receiver on the oil gauge. The tube is shown coming out of the gauge in the picture below. Is this a physical hydraulic connection from the gauge to the oil system? The terminal with wires attached to it go to ground. That's the starter switch next to it.
I can't find any way for power to get to the gauge. When the electric fuel pump was wired into the engine, might wires that went to the gauge have been redirected to the fuel pump, relying on the automatic shutoff in case of a problem?

[Loki9]

That looks like a mechanical oil pressure gauge in the photo, no electric power required.

The ground wires might be there for a night light, which would require a +12V wire (missing in the photo).

Oil pressure safety switches are standard equipment for most electric fuel pump installations. No oil pressure = fuel pump off. Under normal operation, cranking the engine to start it will build enough oil pressure to close the switch and turn on the fuel pump.

[JOHN COOKSON]

The mechanical OP gauge tube from the engine might have air in it that is compressing which would result in the gauge not reading. Start the engine, let the connection to the meter loose and let the oil pressure burp any possible air out of the line then reconnect.

Then again the gauge might be shot.

TRUE GRIT

Edit: To bleed the line:
Start the engine and hold a rag under the fitting at the meter and loosen it a bit until you get a steady flow of oil. Then tighten it back down while the engine is running. If the OP gauge doesn't read after this you'll need a new one.