Charging System Troubleshooting--Blown Ignition Light Fuse?

[ACHiPo]

I'm pretty confident I've eliminated the short, although I suspect I still have a problem with the fuel sender. It almost acts like the fuel sender was acting as a short, but when I cut the wire it somehow reset itself?

Everything is now hooked up as it was delivered with the exception of the pink wire going to the fuel sender, which is floating (disconnected).

The ignition light works properly and the charging system is working correctly. I've run the engine for several minutes, and even took the car for a drive around the block and everything seems to be working correctly (except the fuel gauge).

The fuel gauge worked when I jumpered between the pink wire and the (floating) case of the voltage stabilizer. It also worked when I disconnected the jumper and grounded the case of the voltage stabilizer. I noticed on the test drive (about 5 minutes after the gauge seemed to work) that the needle had dropped back to E.

It seems like the sender pink wire wants to be grounded? I wish I knew why it's changed.

I don't have a problem with that if it works and doesn't cause another problem, but I think I'll hold off making that mod until I talk to Bob Tuesday.

[patrickt]

Originally Posted by ACHiPo

It seems like the sender pink wire wants to be grounded? I wish I knew why it's changed.

I don't have a problem with that if it works and doesn't cause another problem, but I think I'll hold off making that mod until I talk to Bob Tuesday.

On the schematic, the pink wire is hot for a tube-type sender. From the schematic, if you grounded the pink wire it should blow the fuse....

[ACHiPo]

Originally Posted by patrickt

On the schematic, the pink wire is hot for a tube-type sender. From the schematic, if you grounded the pink wire it should blow the fuse....

Yep. And yet...

The mystery continues...

[patrickt]

Well, it could be the sending unit. With the pink wire disconnected, everything except the fuel level meter works perfectly. So, I would try running a fresh, temporary, fused wire to the pink wire connection at the fuel sender unit. Disconnect the existing pink wire at both the dash end and the fuel tank end (just in there's a chaffing fault along it somewhere). Put a five amp fuse on the new fresh wire and run it to the pink terminal at the sender unit and then see if: 1) the fuel level gauge works when the car is on, and for how long, or 2) whether that new fuse blows. If the new fuse works for a while, and then blows, upping the amp value of the fuse might be a possibility to consider... but it is the fuel tank....

[ACHiPo]

Originally Posted by patrickt

Well, it could be the sending unit. With the pink wire disconnected, everything except the fuel level meter works perfectly. So, I would try running a fresh, temporary, fused wire to the pink wire connection at the fuel sender unit. Disconnect the existing pink wire at both the dash end and the fuel tank end (just in there's a chaffing fault along it somewhere). Put a five amp fuse on the new fresh wire and run it to the pink terminal at the sender unit and then see if: 1) the fuel level gauge works when the car is on, and for how long, or 2) whether that new fuse blows. If the new fuse works for a while, and then blows, upping the amp value of the fuse might be a possibility to consider... but it is the fuel tank....

Sometime overnight I remembered Doug telling me to remove the connector behind the driver's side rear wheel and short the forward pink wire to ground. If the gauge responded it meant the fuel sender was bad. (This was several weeks ago when I just had a flaky gas gauge).

My guess is that the gauge was not reading correctly yesterday, but was just responding to having the pink wire grounded. If that's the case, then the gauge would have continued to climb to full given enough time.

So I definitely have a bad sending unit.

I still don't understand what happened to the short? I like your idea of running a separate fused wire to to the pink sender, although I think I will try inserting the fuse where I've already cut the wire. I can run a 5A fuse in that wire and a 15A in #3 so the fuel sender fuse would blow first and not impact my charging.

I'm also going to call Bob and Peter first thing tomorrow and get their ideas.

I think I need to drop the tank to replace the sender? At a minimum I will need to get the car up on a lift to access the sender wire at the sender if it seems there is a chafed wire.

[patrickt]

Originally Posted by ACHiPo

I still don't understand what happened to the short?

Here is what I believe may have happened: The pink wire that goes to the sending unit from the BATT terminal on the tach normally has 12v+ and is also connected to the green wire there at the BATT terminal as well. When your fuel tank sending unit started to fail, that 12v+ on the pink wire starting shorting to ground, through the sending unit, which blew the fuse #3 and caused all the problems on the green wire circuit. If you try and connect a short, fused wire to that pink wire connector going to the sending unit (and make sure the pink wire that goes to the BATT terminal on the tach has been disconnected) and the fuse either immediately blows, or the fuel gauge works for a while and then blows, then you have found your fault and it is in the sending unit.

[patrickt]

I have never had to pull the fuel sender, but it is in the center-front section of the fuel tank. Ask Bob and Doug if there's a short cut to working on it. The manual cautions against using non-gas resistant sealant on it, which makes sense....