Charging System Troubleshooting--Blown Ignition Light Fuse?

[ACHiPo]

Dan,
Thanks. I've basically taken a 3 month hiatus. Just now getting back to it. The fact that it almost kinda works makes me think I'm definitely gaining on it. As the joke about the optimistic kid goes, "there's got to be a REALLY COOL PONY under a pile of poo this big!!!"

[ACHiPo]

Pink wire taped off. Fresh good fuse in. CB and test light out of the circuit. Key on--no light, fuse blown.

[patrickt]

Originally Posted by ACHiPo

Pink wire taped off. Fresh good fuse in. CB and test light out of the circuit. Key on--no light, fuse blown.

Good. Disconnect the wire running to the charging light on the dash and repeat the test exactly. Let's see if it again blows the fuse.

[ACHiPo]

I'll try that tonight when I get home.

[patrickt]

Originally Posted by ACHiPo

I'll try that tonight when I get home.

... and if disconnecting the wires to the charging light allows the key to be turned "on" without blowing the #3 fuse then we will use your new gizmo, along with a dedicated temporary feed, to track down the fault that is on the charging light/voltage regulator path of the circuit.

[ACHiPo]

Disconnected the double green wire from the ignition light, replaced fuse, turned key. Blown fuse (ammeter jumped then dropped to 0).

Disconnected the 10 ohm jumper and the single green wire (ignition light and jumper completely out of the circuit). Replaced fuse, turned key, fuse blew.

[patrickt]

Originally Posted by ACHiPo

Disconnected the 10 ohm jumper and the single green wire (ignition light and jumper completely out of the circuit). Replaced fuse, turned key, fuse blew.

Alright, leave the ignition light and jumper completely disconnected, taped off, and out of the circuit. We will now try and use your tool to locate the short. Coming off of Fuse #3 there are two "legs." One is a W/G colored wire and the other is LtG colored. The latter goes to the heater switch. The former goes to the wiper switch where it becomes a Gn color and from there forks off to the wiper motor and fuel/tach gauges, respectively.

What we will try and do with your tool is to get an idea about where the short is along these lines. Once we get it in the ball park, we can definitively isolate it with a surgical cut to a wire that is easily mended. Put your tool across Fuse #3, turn the key on and observe the circuit breaker clicking on and off. Then put the inductive gauge along the wires as they pass through the firewall and traverse along the path above. Make a note of the behavior of the gauge along each portion of the circuit and report back.

As you're doing this, keep an eye out for an "easily cuttable and mendable" spot on the green wire. I know you don't like the idea of snipping wires, but it's likely that we'll end up doing that. And cutting anywhere along that line limits the potential short locations.

[ACHiPo]

Originally Posted by patrickt

Alright, leave the ignition light and jumper completely disconnected, taped off, and out of the circuit. We will now try and use your tool to locate the short. Coming off of Fuse #3 there are two "legs." One is a W/G colored wire and the other is LtG colored. The latter goes to the heater switch. The former goes to the wiper switch where it becomes a Gn color and from there forks off to the wiper motor and fuel/tach gauges, respectively.

What we will try and do with your tool is to get an idea about where the short is along these lines. Once we get it in the ball park, we can definitively isolate it with a surgical cut to a wire that is easily mended. Put your tool across Fuse #3, turn the key on and observe the circuit breaker clicking on and off. Then put the inductive gauge along the wires as they pass through the firewall and traverse along the path above. Make a note of the behavior of the gauge along each portion of the circuit and report back.

As you're doing this, keep an eye out for an "easily cuttable and mendable" spot on the green wire. I know you don't like the idea of snipping wires, but it's likely that we'll end up doing that. And cutting anywhere along that line limits the potential short locations.

Patrick,
Got it. I will try it this evening. I assume based on Gary's comment that I should not be using the test light in series?

From my rudimentary schematic reading skills, it looks like by disconnecting the ignition light the VR has been eliminated as a potential root cause (or at least not the only cause) given the fuse still blows? Given that the pink wire takes the fuel sender out, it could only be the fuel gauge, heater, or wipers (or wiring between those)?

Evan

[patrickt]

Correct. You do not use the test light in series, but you could have it tapping off the hot side of Fuse #3 and the other lead of the light going straight to ground. That would be fine.

You are also correct that by removing the pink wire from the fuel sender and the wires from the charging light (and the 10 ohm shunt) that you have eliminated the fuel sender, charging light, and voltage regulator from the equation.

What's left is the wiper motor and switch, tachometer, fuel gauge, and heater and switch, along with the wiring and plugs that connect it all. You have a 10v Smiths voltage supply under there too. We won't forget that.

[ACHiPo]

After a bit of caffeine I decided to try it this morning.

I hooked up the CB across fuse 3 without the test light. Sure enough it clicked right after I turned the key!

I positioned the inductive meter over the y/r and w/g wires. When the CB reset, the needle swung strongly toward the fuse (toward the ignition switch).

[patrickt]

Perfect. The gauge is showing that current is running through those wires and, somewhere down the line somewhere, that current is shorting out to ground. Once you go past that shorting out point, there's no more current in the wire (usually). Note that the needle swings in the direction of the current's travel, which kind of "points" to the short. If you flip the gauge around 180 degrees the needle will still swing in the correct direction, but it will now be opposite. March down the circuit's wires, watching the gauge's needle, and see where the behavior changes (like no needle movement at all). If the behavior clearly changes after, say, the connection to the tachometer, then remove that connection. If it clearly changes after a multi-wire connector, then wiggle the connector first to see if you can make the circuit breaker stop breaking, then disconnect it completely if you can't. Don't just wiggle wires willy-nilly though, you might temporarily fix the problem and not be able to figure out exactly what you fixed until it breaks again (which will be the next really inconvenient time and place). The hardest shorts to find are frays/breaks that are inside a taped off bundle of wires, or a goofy behaving multi-connector. That tool will point to the offender though. Now that we have disconnected the pink wire at the fuel sender, and the wires and shunt that lead to the charging light and voltage regulator, here is a list of what I think could be causing the fault (other than a broken/frayed wire or misbehaving multi-connector:

Heater Switch shorting out
Wiper Switch shorting out
Wiper Motor shorting out
The "circuit board" that ERA uses to control the wiper parking
Fuel Gauge shorting out
Tachometer shorting out
The Smiths voltage regulator for gauges shorting out (which I did not originally have, but that I then wired in myself solely to power the fuel gauge). Yes, it does make it more accurate.

[patrickt]

BTW, in re-reading the thread I note that in Post #90 you were able to make the short go away for a while after monkeying around the tachometer area. I would pay particular attention to the wires and connectors there.

[tboneheller]

Unplug each component on the affected circuit one by one until the issue goes away.

[ACHiPo]

Been having trouble signing onto the forum.

Found and fixed at least one problem! The Smiths regulator/shunt was touching a contact behind the dash. Found it as I was tracing wires with the Gauss meter and the CB stayed on after I'd tugged the ground wire I'd attached to the Smiths shunt case. Taped up the leads and got tach, fuel gauge. Reconnected the ignition light and it works as it should!

Of course my paranoia is that I caused that short by removing the Smith's shunt from where it was mounted (it couldn't short the way it was mounted, but I couldn't remount it in the same place with the dash in place). That means there's still a latent short somewhere, unless it is the pink wire? (No I'm not reconnecting that until I get some joy out of having a tach and fuel gauge again!)

Thanks for all your help! Will keep you posted.