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Look on LH inner fender underhood and you should see a junction block. It will have: battery cable from battery to JB, battery cable from JB to starter, a horn relay, and a threaded post with numerous smaller gage wires attached to it. That's where ALL the electrical power for this car is sourced. Check to see those wires are in place, especially a 10 gage red wire.
The factory shop book Joe P showed you will have a full color wiring diagram in it that shows where all power feeds route to.
Good luck!
I have a question about the 10 gauge red wire mentioned above. I intend on installing an under dash ammeter. I will splice into this wire or replace it. Should I use 8 gauge or is 10 gauge enough?
X3 on voltmeter. An ammeter is an easy and unexpected way to burn your car up. A voltmeter is a simple installation, + and - connections and mounting it, and it tells you what you need to know.
I would vote also for voltmeter. Many years ago I had 57 Nomad with an ampmeter. I was in the Navy stationed in Willow Grove PA. Driving home one night on leave I lost all power, no lights, engine died, somewhere in Arkansas. Luckily I was in a town so I pulled over and found the wiring to the ampmeter has loosened and lost contact. Very scary, when I arrived at my parents house, a quick re-wiring took place.
Wiring an ammeter does not require running the load of the car through it. Its wired as a secondary monitoring system that reads the differential in load from the generating side vs the fuse box load side. Its wired in some variance of the diagram below.
My only comment is when running an ammeter, be sure to use an appropriate sized fuse (or circuit breaker) in the wiring, as close to the battery as possible.
I disagree Eric. My brother-in-law's 68 GTO almost burned when the something shorted out on the way to our camping spot and the ammeter wire under the dash heated up and caught fire. I think the alternator may have shorted out. We had to use all of our 12 ounce cans of campout beverage to put the under dash fire out. Shake vigorously, point under dash, pull tab, and spray. We both installed fuses in the ammeter wiring after that event.
My '68 442 was purchased out of Dallas. I reserved plane tickets from Tulsa the week before. The morning of my flight, I called the seller and he said he had a problem when retrieving the car from storage. On the trip back to his home, something had shorted out under the dash and caused a fire. A fire truck was called, they clipped some wire under the hood and the car was towed to an impound.
Of course, my plane is leaving in an hour and a half and I have to make a decision on whether I can rig this thing back together in the impound yard, and then drive it all the way back to Tulsa. After asking a few questions, I felt confident that the underdash ammeter gauge had shorted.
I took the risk, flew to Dallas and we drove to the impound yard. Popping the hood, I could see two wires melted, one of which was missing all the insulation. These ran through the firewall and to the gauge set. Turns out, the bracket that holds the gauge to the gauge pod had loosened and grounded out the 10 gauges wires. So, you had the alternator and the battery sending massive current direct to ground. He's lucky the whole thing didn't go up in flames. I just clipped out the best piece of the 10 gauge, and used a couple of PIDG crimp terminals to go directly from the battery to the alternator. Unfortunately, any of the factory harness that had been lying against the 10 gauge was also cooked. I simply parted these wires and bent them away from each other and away from body contact. Somehow, it all worked and I drove it all the way back to Tulsa. I know, I'm an idiot....
Moral of the story - Ammeters are a hazard. A volt meter is less likely to cause a fire. It also provides you with battery voltage when the engine is off and alternator voltage when the engine is running. Pretty convenient and informative compared to a simple amp meter.
Also, as Oldcutlass pointed out, most GM ammeters are small gauge wires with a 4 amp fuse in line. They simply detect the charge or discharge between the battery and alternator. The load is not intended to be carried through this circuit. Much safer than the underdash, aftermarket accident waiting to happen.
By the way, American Auto Wire makes really nice factory fit wiring. I ended up replacing the light, engine, a/c and courtesy light harnesses. That's okay, it was pretty ratty even before the fire.
Last edited by bry593; March 31st, 2019 at 02:56 PM.
My perfect setup would be both an ammeter and a voltmeter. With both you would have all the information you would ever need about your charging system and battery.
March 21st, 2019, 06:29 AM
