Gauge 10 amp fuse issue

[Gerald C.]

I have a 67 and took it to a show last week and shut the car off. I tried to restart it a few minutes later. It gave me some trouble starting after a long ride to the show.

When it finally started, the battery gauge peaked to full charging. I then shut it off and sat for a couple of hours and the battery gauge was back to normal. It started right up and the car runs great. However, on the way home I noticed the temperature wasn't registering and the gas gauge didn't move from 1/2 full or just over.

The manual showed how to test the temperature gauge and it was grounded properly. Then I tested the electrical connection and had a weak signal. The 10 amp fuse was blown so I replaced it. I restarted the car and the fuse blew again. I replaced the sending unit and the fuse blew again. The wiring is brand new so there is not an issue there.

I do not have a spare sending unit to test the gas gauge. But the gauge did work for the most part before the "charging" incident.

I can't think of anything else to check and are these two gauges related "electrically"?

Thanks

Jerry

[William C.]

Re: Gauge 10 amp fuse issue

You have a short. You need to study the wiring diagram and find out all of the circuits that are fed from this fuse and trace the circuits to locate the short. Likely the issue is in the wiring as opposed to individual functional components.

[Edward B.]

Re: Gauge 10 amp fuse issue

I agree with Bill. And the problem may be a pinched wire. A few months ago I had to disconnect my tachometer, and when I put it back on, I pinched one of the grey dash light wires between the tach cable and the receptacle, grounding it out. The first time I turned on the dash lights, I popped the little 3 amp fuse. Took me awhile to find my mistake!

Ed

[Gerald C.]

Re: Gauge 10 amp fuse issue

Bill & Ed,

I traced to circuit to the fuel gauge and the ignition. There was no movement around those items that would create a pinched wire or a short. The wiring is brand new! As I mentioned, when I restarted the car at the show, the battery gauge was pegged to charging and then after a while I restarted the car and the battery gauge was fine.

How will I check for a short in both the ignition switch and the fuel gauge? Sorry, but I'm a novice when it comes to electrical challenges!

Thanks,

Jerry

[Edward B.]

Re: Gauge 10 amp fuse issue

Jerry, I'm not that good with electrical issues either, so I'll have to bow to someone more informed than I

Sorry I couldn't be of more help.

Ed

[Dan D.]

Re: Gauge 10 amp fuse issue

Jerry,

I would start by disconnecting the battery and using a ohmmeter, check for low resistance between the gauge wires and ground. I don't know what the resistance should be, but if you get something at or near 0 ohms, then you are on your way to isolating your problem. Take it one step at a time, and report back and we will walk you through it.

-Dan D.-

[Gerald C.]

Re: Gauge 10 amp fuse issue

I tried to find this but couldn't. I brought it a shop near me who has a 15 year Corvette mechanic. He's tried for a day and a half to find it and came up with nothing yet. His idea seems to be in the wiring harness itself. (Not a pretty thought!) He's going to spend more time today. He even took the cluster partially out and couldn't find any issues!

[Steve G.]

Re: Gauge 10 amp fuse issue

I'd be very surprised if it's in the harness. You need to identify everything that works off that fuse and disconnect them and the harnesses leading to them one at as time. I took a quick look at the diagram in the 67 AIM, which is a pretty poor diagram, and I can see that the hand brake warning light also is on that circuit. Should pull the console and see if you caught the wire pulling the brake on. I'd have to do a little more research to see what else is on there, but that will give you something to go on.

I put a buzzer in series across the fuse holder when I'm doing this. As long as their is a dead short the buzzer will sound. You unplug the various components in the circuit until the buzzing stops. Ie, unplug the rear body wire harness. That eliminates not only the sending unit but all the wiring travelling back from the body connector. Then unplug the bulkhead. By following the wiring diagram and unplugging the various harness that contain that circuit you will isolate the section containing the problem. Usually doesn't take that long to narrow down a dead short.

Steve

[Gerald C.]

Re: Gauge 10 amp fuse issue

Steve,

I think that is the only thing that wasn't checked out. Seems logical that that wire could get pinched in the gear mechanism. We'll check it out in the morning.

Thanks!

[Steve G.]

Re: Gauge 10 amp fuse issue

If someone could post the wiring diagram out of the service manual I could probably give you a few more directions to look. The AIM diagram shows that the circuit off that fuse splits off into five separate circuits. One goes to the temp gauge, one to the fuel gauge,both at the cluster.
You can eliminate the portion of those circuits from the dashboard gauge to the senders in both cases because the load resistance is prior to the sending unit. A grounding out (short) in either of those wires to the senders or their sending units themselves will simply peg the gauge and will not blow the fuse. The sending units can ground the circuit completely to make the needle move to one end. If the problem is with the instruments it has to be in the cluster or between it and the fuse.

One of the other branches goes to the park light warning bulb. Again, the problem would have to be between the fuse and the bulb. A short at the handle would only cause the light to go on. The short has to be between the fuse and the bulb ( load).

Another branches through the firewall and appears to go to the back up lamp circuit. Here the short could be anywhere between the fuse to switch and switch to rear bulbs.

The last branch goes to a body connector to the rear and I can't see where it goes from there. need a better diagram.

Steve

[Steve G.]

Re: Gauge 10 amp fuse issue

See my correction on that below. Look at the bulb. Backup lights certainly have the greatest opportunity for a problem. Longest run of live wire. I'd really like to know where that 5th branch goes tho.
Steve

[Gerald C.]

Re: Gauge 10 amp fuse issue

Steve,

This harness is about a year old and everything worked fine until I restarted the car at that show and the ammeter pegged to positive and then was fine after I started the car a couple of hours later. Give me good old mechanicals anytime!

Jerry

[Steve G.]

Re: Gauge 10 amp fuse issue

Steve,

This harness is about a year old and everything worked fine until I restarted the car at that show and the ammeter pegged to positive and then was fine after I started the car a couple of hours later. Give me good old mechanicals anytime!

Jerry

Is it no longer burning the fuse?

The gauge pinning likely had to do with the dead short that is blowing the fuse. When the short first occurred the alt was trying to supply the high amount of current going to ground. Once the fuse burned both the gauge went out and the high draw stopped.

I wasn't so keen on mechanical gauges after the time I felt something drip on my nice clean pants on my way to pick up a date with my first 63. The oil gauge line had cracked at the gauge and was dripping all over my nice clean pants and the new carpet.

I don't think there's anything wrong with the harness. It's a small thing, just have to persevere to find it.

Steve

[Gerald C.]

Re: Gauge 10 amp fuse issue

Update: Well the problem was that I had a bad fuel sending unit (or it got fried). I replaced it and all is well with the world!