'74 SB Alternator

[cdbrush]

I have a '74 convertible that I have recently started to restore. I have an alternator question. The (white) regulator is fastened to the top, it has (3) wires terminated. A red to the D+, a green to the DF and a brown that I connected to the D- on the side of the reg. All three run as far as underneath the back seat where they are cut off. I connected the red from the D+ to a blue that runs up to the warning light. The Bentley wire diagram shows the green and brown connected to (I'm not sure) a resister of some type?
Is anyone familiar with or know where they go or what that black box symbol is on the Bentley? I sent a e-mail with pictures to Speedy Jim but haven't received a reply yet.
Thank you for your help...this one is driving me up the wall.

[Marc]

`74 was the year of the transition from the externally-regulated alternator to the more modern style with integral regulator. If you had the former, with three slip-on connectors (bottom one in the picture below) you would need a voltage regulator under the back seat, mounted just aft of the B-pillar, about the size of a pack of cigarettes.
It sounds as though yours was replaced with the integral-regulator Motorola (top one in the picture). If that's the case, you only need to use one of the wires in the harness between the alternator and the back seat area, just to connect to the blue wire there that goes to the warning light. It doesn't really matter which one you use - I prefer to use the green but the red one works as well (so long as nobody working on the car in the future tries to hook it up to B+ along with the big red wire). As a bonus, you now have two extra wires that can be used for a tach or gauge if you ever add one.


The gray rectangular box in the Bentley wiring diagram (with a transistor symbol on it, labeled "C1") represents the external regulator. The diagram was never revised to show the later setup, since electrically they're identical - the regulator was simply physically moved from under the back seat to atop (or inside) the alternator.

[aussiebug]

Yes - if there are more that two wires (thick red plus thin green) connections on the Alt, then your car had/has the external-regulator version of the alternator.

As Marc pointed out, if you now have the internal regulated version, you only need the red connected direct to the battery and car's electrics (usually via a strong 3-way connection under the back seat), and the green wire connected to the blue wire under the back seat, which goes to the Alt light on the dash.

If you still have the external regulated version, it needs the regulator under the back seat, but it MUST be an alternator-regulator. The old style generator-regulator will NOT work.

For info, you MUST have a working Alt light in the dash, or the alternator will not charge the battery - it uses the tiny current through that light when you turn the ignition on, to excite it into action with the engine running.