Alternator light

I too think this is what happened.

The diodes are usually sold already mounted on a 'diode bridge' or whatever it's called, which is a good thing. A normal home soldering pen won't be strong enough to reliably attach them anyway.

The Alternator can be taken apart and the diode bridge replaced, with more or less normal hand tools. (a big 36mm socket is needed to break the fan nut loose, and without a fabricated special tool to hold the fan/shaft still, you risk twisting the shaft or breaking it.. been there. Do NOT use an impact gun.) Plus I think you still need to get a powerful soldering gun to get the bridge wires disconnected and reconnected.

While there, consider replacing the bearings too.

With all the labor and some tools needed that you may have to buy or rent or ste... borrow from someone, it may well be worth looking into rebuilt units, or even brand new.

The fan holder tool you can make yourself if you have some basic metal working skills and a welder:

internally or externally regulated alternator(74 was a mixed year)?

Thank you Jim and Jan for such quick responses. I an employed as a forklift mechanic in a warehouse and have rebuilt DC motors so I may attempt this one if I can locate a new diode bridge. I have all the tools I could ever need through my employer

As a completely off topic aside. Jim, I owe you a big apology. A long time back I had a stripped bypass air screw on my carburetor. You graciously mailed me a new one. I had a thank you card that I though was mailed to you but found it behind my desk on a recent cleaning. I am truly in your debt for your kindness and feel terrible that I never got that card sent.

Bad news.

Most likely one of the diodes inside the alternator has failed.

Pull the plug off the alternator. Connect a small test lamp (like a speedo illum bulb) from Ground to the D+ terminal.

If the bulb lights, there is a bad diode.

Replacement is not really a DIY job as the alternator needs complete disassembly.

And getting the alternator out on a DP engine usually means pulling the engine, though in a pinch it can be shoe-horned/ crow-barred out.

Speedy Jim

LOL!

All is forgiven.

Jim

Ooooooooo :) Oh, to have worked for Grainger! Sweet.

I'm, assuming you have a Motorola alternator, rather than the Bosch which was used on some '74 cars.

There is a .pdf of the most common Motorola parts here:

Good description of alternator internal wiring:

Excellent step-by-step w/pics, showing alt/gen removal with engine in the car:

Speedy Jim

And a nod of the head to Srogers!, who epitomizes the spirit of RAMVA

-Bob Hoover

Dear Speedy,

'Way back in the dark ages... or the mid-'80's, one of them two, I came up with a heat-sensing circuit that kept an eye on the external rectal frier used on the coaxial rectal frier I installed on most of the engines I built. It had a smart little circuit that decided when hot meant TOO hot... and triggered a big mother of a switch, disconnecting the output of the rectal frier from the load. Turn off the engine, you prepped the circuit to fire IF the output was greater than 50 degrees F more than the ambient temp, AND the temperature of the rectal frier was fifty degrees hotter than ambient.

-Bob

HaHa! That must have been monster selenium rectifiers on (maybe) a Leece-Neville alternator?

And glad to see that your sense of humor has not been diminished in the slightest!

:)

Jim

I happened to have a Motorola alternator all apart and took some photos. In this model, the diodes are staked to the alum heatsink and would have to be replaced as a complete bridge.

Speedy Jim

_________________________________

Prolly Leece-Nevilly... the red ones you could pick up by yourself, vs the gray ones which you couldn't.

But I had one hell of a time convincing the over-educated electronics type trying to keep those tube-type Motor-roller Monstrosities we had to install in our Shore Patrol pick-ups running soz we could have cross-frequency compatibility , that our 24volt 'generators' were actually ALTERNATORS or, crazier still, DYNAMOS, despite the screaming fits of college-diploma'd rage. Worse job in the world, pulling duty with those folks even if was only one in four. I guess Father Timex prolly ruled in our favor.

Long time ago, Jim. Long time ago.

-Bob Hoover