The Stovebolt Site Forums The Shop Area The Electrical Bay This is downright wierd!

Has anyone ever seen a 1971 truck wired for both the early style external reg alternator AND for the later style internal reg type? This 1971 C-10 is turning into a real learning experience. So far, I have seen almost every mistake one can make electrically with setting the truck on fire! This "dual" alternator wiring takes the cake. I have the "--" type plug on the passenger's side with the correct color coded wires just laying on the intake doing nothing and the "II" type plug on the drivers side with the alternator hooked to it. The alt seems to charge the battery but the case is cracked and the cover is almost rusted off the reg.

It looks like every previous owner with 3 feet of wire and a box of scotch locks has figured that he was smarter than the Chevrolet engineers. I dread cutting into the harness to see what has been done, considering that I found 9 (nine) scotch locks in the rear wiring and an extra 15+ feet of wire. There was a "hot with the brake lights" wire going to the front right behind the battery with a fuse holder at the end! Yes it was still HOT!

Anyway, any thoughts why there are two different alternator plugs? I know they can't both work.

best wishes,

Les

Sounds like you've got a "Frankentruck" there! I really love straightening out other folks' wiring mistakes before I start making some of my own! If you're going back original, or close to it, find an original wiring diagram and try to follow it as closely as possible, eliminatind extra wiring as you go.
Jerry

Thanks Jerry, but that's gonna be tough. It looks like a monkey jungle under the hood and dash with vines going everywhere. I guess I can probably remove the household lamp cord without a diagram, though.

Really, you give good advice and I plan to follow it.

What gets me is the alternator wiring for both looks factory. What I'm guessing is that somebody spliced part of another harness in at some point. Why I don't know.

Best wishes,

Les

The type 1D alternator with the external regulator would have been the original-equipment application. With the exception of the main charging lead from the alternator to the battery, I don't think any of that wiring would be needed to connect the 10SI internal-regulated alternator. There are several varieties of regulator units available for the 10SI, and some need external excitation while others are self-exciting, needing only a jumper wire from the battery terminal to connector #2 of the regulator. Connector #1 is an idiot light ground, and usually isn't absolutely necessary unless you plan to use the dummy light. My Massey-Ferguson tractor is set up that way now, and only requires a quick goose of the RPM to begin charging after startup.
Jerry

Bought a '70 car once, it was wired half for one year, half for another, and neither was the right year! It got so bad I just unplugged everything, got the correct diagram, and plugged it all back in wire by wire. Crazy part was it worked and never gave me issue for 13 years.

My old bolt was a nightmare, lots of "extra" wires, and at some point some shade tree engineer had decided fuses were for sissies. This person took everything that required power, ran a large wire from the batery, & tied all of it together with a monster wire nut,... It was a minor miracle anything worked (a lot didn'tA). I gave up trying to fix that mess and yanked it all out and made a new harness from scratch.

Sounds like somebody got a "deal" on an alternator and harness in a Meijer parking lot one night when their alt died. They ran in and got some scotch locks and another 12 pack, installed it and now you have two hookups. Mystery solved!!! Good stuff.

Howdy 561tonpanel,

What you suggest wouldn't surprise me except I bought it from a cop who'd had it a while. Who knows, he lied in about half of what he said so maybe. It did have the original type alternator in place on the original bracket when I got it.

That's a nice and unusual panel you have.

Best wishes,

Les

NOOO! A cop lied about something he sold,
Go figure.

Whatever makes them look better at the time. Cop would rather lie when the truth sounds the best. Thanks for the complement on my panel. She does seem to be an oddity. I cant find any like her.

Can you see where the 2nd alt harness was scotchlocked in? I know some tractors had both harnesses in transition years but they would be on the same side.. not one on each side as they didn't move the alternator when they converted from a 10DN to a 10SI.
ps I know where theres a GMC pannel like that one.

if that wiring was addd later it was probably for a "low budget" fix meaning they had a alt. laying around and wired it in to use it, i have done it before and left the modification.

Maybe the alt went bad and someone had one the other style on hand and never did anything about it .

I want to thank everyone who responded and apologize for not revisiting this thread earlier. What this wiring was has been solved! I was talking to an old time ex dealer mechanic and I asked him about the extra wiring. He said no, that the wiring had to hook up differently like hotrod lincoln said. He asked if I had some "unknown" relays on the firewall on the drivers side. I had those relays, I said. He told me that it was probably the TSC (Transmission Spark Control) harness and that it probably wasn't hooked to anything any more. TSC was an early emission control system that controlled vacuum advance, but it was still hooked to the hot side of the coil. The plug would fit a 10si alternator, but since there weren't any in '71, there was no problem with mistaking plugs. It just happened that the TSC harness ended up laying along the inside of the right hand rocker almost like the alternator harness! Anyway, it is all gone now and everything works fine. Strange, huh?

Best wishes,

Les

Yep, I remember the TCS system. It only allowed the vacuum advance to work under very specific combinations of speed and engine temperature. The GM engineers had found that it was possible to reduce unburned hydrocarbons by retarding the timing a little, and the easiest way to do that was to prevent the vacuum advance from working in the part-throttle ranges. A speed-sensor switch and a vacuum valve kept the intake vacuum away from the advance chamber unless the speed was above a certain limit or the engine started to overheat. Then the vacuum would get switched to the advance, and it would operate and cool the engine down due to higher idle speed and fan volume, plus the earlier timing kept the combustion chambers and exhaust manifolds cooler. Some of those early emission control systems were real Rube Goldberg operations that almost guaranteed lousy gas mileage, even if the engine did run lean enough to pass federal emission requirements!
Jerry

Thanks for the specifics, Jerry. I'm getting most of the "frankentruck" stuff figured out or fixed or whatever. Man, does the '71 drive better with power steering and power brakes! I have had a long, hard lesson in the differences between Canadian and USA engines, too.

Thanks to all for the feedback!

best wishes,

Les