I often find the hardest part of fixing this beast is LOCATING the relevant wiring.

Splices inside wiring harnesses, wires that change colors U-turn wires... that Chevy engineer really did his best to lose anyone trying to trace a circuit.

Ok, for the Ammeter in a 1968, two wires... (black, black & white stripe IIRC)

Where do they tie into the harness under the hood. Can I assume ONE of them comes via one of the fusible links coming off the horn relay?

What about the other? Perhaps the fusible link up in the middle of the harness behind the engine?

I've got a dead ammeter; before I order a replacement I want to check out the wiring.

Thanks.

 

This is for a 69 but should help you figure it out.
Note that the shunt wire A>B is resistance wire.
Note also if you tested your meter and it's "open" they can repaired by disassembling and carefully soldering the broken "hair-fine" wire back.
They usually break right at the first turn - unwind one turn and put a drop of solder on it.

 

If you check BOTH wires in the connector for your ammeter and you have 12 volt positive on them...then it is the gauge.

DUB

 

Still looking for the PHYSICAL location where the black wires come off the main harness via fusible links.

One appears to be from the horn relay. I've got two fusible links coming from there so I'll have to figure out which is which.

 

The connection points for those two ammeter wires are INSIDE the primary power line in the engine compartment. Unless you understand HOW it works, you can't really get your head around why it is wired as it is. BOTH ammeter wires are connected to the same primary buss wire!! But, they are separated by 18" [or so] of that wire. So, as mentioned above, if you measure [[approx] 12 vdc between EACH of those wires to electrical ground (-) {those wires must be disconnected from the gauge}, each will measure nearly identical 12 volts.

The "trick" GM used here is that the 18" [or so] of that main power wire DOES have a small resistance between those two connection points. That means that current flowing in one direction thru that wire will have a slightly higher voltage reading than at the other connection point....only by a few millivolts because that resistance is so low. If you use a simple galvanometer to "read" that voltage differential, you can get it to swing + or - depending on which way current is flowing thru that wire (+ if charging current; - if current is draining).

Voila' !!! Calibrate the meter scale to read AMPS to match the actual current flowing thru that line and you have a pseudo-ammeter -- a cheap galvanometer which is scaled to read AMPS. Very effective, inexpensive, and reasonably accurate (+/- 5 amps, maybe). And, there really is a VERY low amount of current actually flowing thru the ammeter and its wires (those feeder wires are 16 awg wires, I believe.

If you NEED to find the connection points in the wiring harness, you will have to tear the wrap off of the main trunk wire and search for them. But, I would NEVER go that way if each of those wires has [about] 12 vdc on them. If so, the problem is NOT in the engine compartment harness.

 

Thanks 7t1vette, I do understand HOW it works. If you'll look at my comment in this thread hopefully that will confirm to you my understanding.

https://www.corvetteforum.com/forums...amp-gauge.html

I've got the wrap off the main harness (for other reasons) and I believe the fusible link in the main harness (orange), directly behind the motor is supplying signal to one side of the ammeter. Just trying to confirm that physical location. Doing everything I can up top BEFORE pulling the dash apart again.

The engine wiring harness on my '68 has been "messed with" by so many clueless folks over the years. I have a half dozen "dead end" wires sticking out of the main harness. For example, when one PO (previous owner) installed an electronic ignition, the starter feed going to the ignition coil became unnecessary. I've identified all but one or two of the dangling wires. But I'm not going to put the main harness into loom or re-wrap it in tape until I have ALL of the loose wires identified, I've also had to replace a few wires that were in bad condition -- cracked, or rock hard insulation; or ends now too short from multiple repairs.

I suspected that at some point along my repairs the ammeter would simply start working but so much is fixed now I'm suspecting the gauge itself.

Chevrolet connecting all the 12V power lines at the bottom of the horn relay was an incredibly ugly way to do things; I plan to install a bus bar for power but need to keep the connectivity the same SO things like the ammeter continue to function. Amazingly enough none of my fusible links were fried even though a couple didn't look so good --- the one by the starter had a previous repair. I had been guessing one of them would be the cause of the inoperative ammeter.

 

I think you still don't understand how your ammeter works. The ammeter needs NO POWER CONNECTION. The signal line are connected to the power line, but not to 'power' the ammeter. Those two lines only measure voltage differential across the length of power wire running between them.

I will say this one last time: If you measure 12vdc (approximately) on BOTH of those ammeter signal lines THERE IS NO REASON TO DIG INTO THE HARNESS WIRING because there is nothing wrong with it.

 

See private message. Thanks.

 

LOL, yes you are correct in your assumptions. One of the wires connects to the horn relay and the other wire is spliced to the main power wire that runs from the solenoid to the horn relay at the firewall behind the engine.

 

Hello. I have somewhat of a related question. My ammeter seems to be stuck at just a hair over “0”. It doesn’t move in either direction at all when driving under normal conditions. A few notes:
1) the alternator is working properly, tested separately
2) the ammeter did move to the left when ignition “on” with headlights turned on
3) battery is new
4) I believe it used to move back and forth a little when driving


thoughts? How to test further for a faulty gauge?

thanks!

 

wadenelson
On my 68
-1 fusible link was in the bundle immediately to the driver side of the wiper motor before the lead heads into the bulkhead and into the cabin.
-Other fusible link was in the lead that connects to the horn relay.
Check these 2 areas. I have replaced multiple fusible links. I buy replacement fusible links (leads) at my local autozone since its nearest. Solder them in (use a heat sink while doing this) and heat shrink the connection.
I can get a picture if you really need one. Lemme know.....but anyway....

Here is my story: I only mention this so as to not send you on a wild goose chase. The reason mine had an issue is because there was another fusible link at the starter post where a fusible link had separated/blown---not a typical scenario since I had a parallel lead going around the front to feed my electric fan and then connected in parallel to the starter post.

https://www.corvetteforum.com/forums...locations.html

 

Jmc2112
If it deflects when the headlights are turned on, then it's probably ok, but I suggest the following check just to verify.

You can turn the headlights to ensure it deflects, and then activate the "flashers" to see if it deflects intermittently.... or the brakes since it's quite sensitive-- mine deflects each time I use the brakes.

 

Since you don't tell us what year model you have it's difficult to provide accurate guidance.
If it moves negative when you turn on the headlights (car off) then it's working.
If you have a good battery and the car starts easily then you shouldn't see much movement from the meter once the car is started.
If all's well then your meter will sit just right of center.

 

Thanks to all. It does sit just right of center! It’s a 1968 L-79 (327/350). Feedback appreciated. Good to know all is well.