The Return of Rusty

[ClayJ]

The trailer brake controller?

Take a look at the fuel gauge, ammeter. Then notice that there is no key in the ignition. Shouldn't both those gauges be dead with key off?

[ClayJ]

100 RPM idle speed?

You are right on the tach being off, should show 0 when it's not running, but even with the engine running it's still showing 100. I'm wondering if that could be connected to the fuel and ammeter gauges being live with key off.

[Gary Lewis]

Take a look at the fuel gauge, ammeter. Then notice that there is no key in the ignition. Shouldn't both those gauges be dead with key off?

As Jim pointed out, the oil pressure, fuel level, and water temp gauges are actually thermometers. There's a heating element in them and the current from the sender heats that up and the gauges slowly climb. So you could pull the key out and the gauges will slowly fall. Takes maybe 2 minutes to completely cool off.

But the tach never did sit at 0 when the key was off. However, it was fairly accurate when the engine was running. I don't know why.

[ArdWrknTrk]

You are right on the tach being off, should show 0 when it's not running, but even with the engine running it's still showing 100. I'm wondering if that could be connected to the fuel and ammeter gauges being live with key off.

Clay,

The three gauges are powered by a tiny oscillator known as the Instrument Cluster Voltage Regulator.

This creates a square wave that averages about 5 1/2V.

Gary has done a great write-up about using a solid state Swad-j (?) Buck converter to replace the old fashioned contact point unit.

But the cluster shouldn't be seeing any power with the key off.

Those instruments are adjustable, but they shouldn't be reading like that (unless someone was messing with them)

For sure everything was right when Gary sold the truck.

And you say it's been sitting in storage since. :nabble_anim_confused:

[ClayJ]

As Jim pointed out, the oil pressure, fuel level, and water temp gauges are actually thermometers. There's a heating element in them and the current from the sender heats that up and the gauges slowly climb. So you could pull the key out and the gauges will slowly fall. Takes maybe 2 minutes to completely cool off.

But the tach never did sit at 0 when the key was off. However, it was fairly accurate when the engine was running. I don't know why.

I can say that this picture was taken when the truck hadn't run for over 12 hours. Also, shouldn't the ammeter be in full deflection to discharge until the ignition switch is placed in acc on?

[ArdWrknTrk]

the tach never did sit at 0 when the key was off. However, it was fairly accurate when the engine was running. I don't know why.

Its probably disconnected Gary.

Somewhere, that green wire from the coil is open.

I don't know why.

 

[ClayJ]

Clay,

The three gauges are powered by a tiny oscillator known as the Instrument Cluster Voltage Regulator.

This creates a square wave that averages about 5 1/2V.

Gary has done a great write-up about using a solid state Swad-j (?) Buck converter to replace the old fashioned contact point unit.

But the cluster shouldn't be seeing any power with the key off.

Those instruments are adjustable, but they shouldn't be reading like that (unless someone was messing with them)

For sure everything was right when Gary sold the truck.

And you say it's been sitting in storage since. :nabble_anim_confused:

Jim,

I've seen the write up on the IVCR and wondered if that could be the common link. Yes, Rusty has been sitting in my FiL's shop since buying from Gary. I have no doubt everything was working when sold, for example the tach just stopped working a few days before I went to pick it up when the mechanic was test driving for the flexplate.

[ArdWrknTrk]

Jim,

I've seen the write up on the IVCR and wondered if that could be the common link. Yes, Rusty has been sitting in my FiL's shop since buying from Gary. I have no doubt everything was working when sold, for example the tach just stopped working a few days before I went to pick it up when the mechanic was test driving for the flexplate.

Those gauges can't read like that with no power.

My only explanation is that somehow the cluster received a full 12V, the springs inside lost their temper and took a set.

But that doesn't happen from momentary abuse.

You have to leave power connected for a minute or more to turn the gauges into light bulbs.

[ArdWrknTrk]

Jim,

I've seen the write up on the IVCR and wondered if that could be the common link. Yes, Rusty has been sitting in my FiL's shop since buying from Gary. I have no doubt everything was working when sold, for example the tach just stopped working a few days before I went to pick it up when the mechanic was test driving for the flexplate.

The 1981 EVTM is here on the site.

You know how to read a schematic.

I'm going to tell you that manual is more of a graphic representation, and that when looking at a circuit you may see a connector (C304) that only shows the wires associated with that one circuit, while the reality may be that the connector carries multiple circuits shown in multiple chapters.

[ClayJ]

Those gauges can't read like that with no power.

My only explanation is that somehow the cluster received a full 12V, the springs inside lost their temper and took a set.

But that doesn't happen from momentary abuse.

You have to leave power connected for a minute or more to turn the gauges into light bulbs.

It doesn't appear that they are set in a fixed position. When driving both the fuel and ammeter gauges worked as advertised. I just happened to notice it when looking at the pictures I snapped of the cluster. Here's a picture under Rusty's hood that shows the firewall near the driver side. The connectors circled appear to be disconnected, any of those the culprit?