Midyear Amp Gauge Question

[PTighe]

My amp gauge was working OK until I took off the horn relay from the radiator support and let it hang loose. I forgot to disconnect the battery and as luck would have it, the hot wire on the relay touched a grounded piece of the engine and it popped and sparked like hell.

No visible damage or smoke, but when I started the engine, the amp gauge pegged out on the 40+ side indicating something was wrong. Now it quit working altogether, it stays at zero, won't charge or discharge. Everything else works fine, did I cook the amp gauge and has anyone ever cooked one before?

Thanks

 

[JohnZ]

One of the wires under a screw terminal on the horn relay (the screw terminal bus on the horn relay is "hot" from the battery all the time) goes to the ammeter, and the other wire from the ammeter goes to the positive battery cable stud on the starter solenoid. Sounds like when the horn relay terminal bus dead-shorted to ground, it also dead-shorted the shunt windings on the back of the ammeter to ground from its feed to the battery through the other wire. It's probably ammeter time.:eyerole

 

[PTighe]

Thanks John, I checked the wiring at the solenoid and found the 10 gauge hot red wire which hooks up at the center terminal, along with the +battery cable, had the fusible link fried. You know the short piece of brown wire had melted.

So I fixed that, and checked the continuity and it was good. Hooked up the battery again, but it still wasn't working. The '67 Shop Manual says somewhere that the ammeter is protected with two fusible links under the dash, so I'll have to find and check those tomorrow. Ain't this a great hobby?

 

[magicv8]

The fusible link that fried protects the "ammeter" shunt - which is the fat wire that the link is on the end of.

The "ammeter" is a galvanometer that is registering the differences beween the voltages at the starter and the horn relay. I will be amazed if it is not fried. My 66 had no protection on the galvanometer until I installed an inline fuse at the meter. The fuse blew this summer when the alternator fried the power line off the harness.

This winter, I plan to convert the galvanometer to a voltmeter. My A-C car has a 63amp alternator (and I am installing a 135amp unit), and the galvanometer reads +/- 40amps. I regard that a cross between a joke and a cost cutting effort. The c1 cars had real ammeters with real shunts. The c2 cars have problems.

 

[JohnZ]

There are no fusible links under the dash protecting the ammeter; they're at the ammeter wire connection points at the starter and at the horn relay. The ammeter wire at the starter is 16-ga. black with a 20-ga. orange fusible link at the connection; the one at the horn relay is 16-ga. black with a white tracer, with a 20-ga. orange fusible link at the connection. Both of these connections have to be good for the ammeter to work.

 

[PTighe]

Dave and John, unfortunately for me both of you are correct. The amp gauge is protected by two fusible links, one at the solenoid and the other at the horn relay.

I checked all the rest of the fusible links and they are OK, what I can't understand why didn't the link that burned up protect the amp guage from cooking?

Well, now it's back to scratch, I'm pulling all the cluster gauges and clock to have them restored, that should set me back $700 and a couple months as slow as I am.

If there is any good part to this story, I'm only a few miles up the road from Corvette Specialties of Maryland; they specialize in restoring cluster gauges and have been doing it for 25+years. All the feedback I hear about them has been good, and I like to place my valuable gauges directly into someone's hands instead of UPS. :eyerole

 

[JohnZ]

Yup, CSoM does great work - they've done a lot of C1 work for me over the years, and they'll get my '67 cluster this winter. Nice folks to deal with.

 

[magicv8]

The "ammeter" is NOT protected by tthe fusible links. The harness is protected by the fusible links, and when a surge is diverted to the "ammeter", the "ammeter" is toast.

IMO, when you install the cluster, insert a 1 amp fuse in either "ammeter" line - if you want protection against a repeat failure. That should be sufficient to protect the galvanometer winding.

 

[PTighe]

Dave, thanks for the heads up on installing an inline fuse to the amp gauge. Once I get it fixed, I may just install a redundant fuse on the other side as well.

My source of information mentioned above is from the '67 Chassis Service Manual, Engine-Electrical, page 6Y-9 which states:

"The ammeter circuit on all models is protected by two orange, 20 gauge fusible links installed as molded splices in the circuit at the junction block or the solenoid battery terminal (Corvette only) and at the horn relay. Each link is serviced by splicing in a new 20 gauge wire as required".

Obviously, this is bad information; as you mentioned, the fusible links failed and did not protect my amp gauge. Thanks