1966 Jetstar 88 330 2bbl. I've replaced the alternator twice on this car and it runs fine for a bit (I don't drive it regularly so maybe 5 or so driving sessions.) Then I take it out on the road and get the gen light on the dash and only 12v at the battery with the engine running. Checking both from batt + to ground and batt + to batt - gives the same result. When I jump the F (dark blue) and hot (red) at the regulator the alternator made a whining noise but didn't put any more juice than 12v. Before I go tearing grounds apart any other suggestions?

 

Where/who is rebuilding/supplying the alternator? New, used or rebuilt? What amperage?

Have aftermarket extra electrical loads been added e.g., stereo amps?

Is there a good condition braided ground strap from the engine clock to the firewall?

 

Car is all stock. The alternator is the new from autozone Duralast Gold 7122N. This is the second one of this model I've had. I haven't traced wires yet (IE checking grounds) as that takes a lot of work for me to do. According to the website it's 55amps.

 

The only things that I know of that have been changed on this car is the air conditioner condenser was replaced at some point (currently disconnected due to a failure,) the driver's side valve cover has been painted due to paint peeling off, rear tail lights, and probably headlights at some point, not counting the alternator.

Oh and the CB radio was removed at some point so that was a mod I'd forgotten about. *at least there is a wire to the trunk and a whip antenna in the trunk. I haven't dug into it any further than that.

 

Those mods/repairs should not affect the alternator. 55 amps should also be ok. Id suggest having the alternator rebuilt by a local independent shop.

 

There are two (minimum) wires you should evaluate: (1) Negative (-) battery terminal to engine block; (2) Engine head to firewall; and, (3) if you have a ground wire from battery terminal to chassis (located near fan shroud metal upright). Ensure the wires themselves are in good condition free of corrosion (consider peeling back the exterior rubber insulation ~6" on each end of each wire for a look). Ensure the wire ring terminals are free of corrosion & the metal where each wire is secured to the block, firewall & chassis are clean & free from corrosion (use a wire brush &/or sandpaper to clean). I'm not certain where your ALT gains its ground, likely its the attachment point from ALT bracket to engine block.

 

Before you go any further, I would suggest you get a 1965 Oldsmobile Chassis Service Manual.
1965 Oldsmobile Chassis Service Manual | eBay
Review the procedure to check the charging system.
Note that this alternator has a remote regulator on the firewall.
This could also cause your problem.

 

I have the chasis service manual and also read testing the regulator here in a really old thread by jumping F and 3 to activate the field at the regulator connector on the firewall. I do not have some of the tools they ask for (a bulb mercury thermometer and the test adapter connector J-21053) and I'm not sure making adjustments to the regulator they suggest will solve the problem but I guess I can look at that when I have a couple hours to devote to it. The main issue is that this works when I first put the alternator in and then after maybe 100 miles of driving the alternator fails. I've even put in a new regulator (which doesn't guarantee a working regulator) and had the same result with the current alternator that's only putting out 12v. (Should have mentioned that in the OP.)

I did find one of the test adapters but they are super not common. I'd try having autozone test the alternator but every time I've tried the local ones they either don't have someone available or don't know how to use the machine. (IE they don't want to.)

For those curious basically what the j-21053 connector does is the same thing that jumping F and #3 (Dark blue and red) on the regulator connector. It runs 12v to the Field connection on the alternator which should if it's working correctly set the alternator to charge. Instead of going through the regulator wiring however it is just a direct connection to the battery terminal*. Page 12-12 in the Chasis service manual.

 

The greatest majority of electrical issues reside on the negative (ground) side of the circuit. The external VR secured to the firewall obtains its ground via connection to the metal firewall; albeit, the importance of ensuring the ground connections (Post #6) are good. Best of luck!

 

Now I need to figure out where the old ground wire on the alternator used to run. There aren't any loose wires in the engine bay at all so not sure when/where it was removed. Looks like something was connected (have what I think is the original delco remy alternator. Finding someone to rebuild it????)

 

 

If it is the original Delco-Remy ALT there will be a part number located on the case which can be validated via a parts manual. I'm not 100% on a 1965 ALT; yet, often an ALT doesn't require the GRD lug/post to be grounded as the ALT is often grounded via its attachment to the ALT bracket which in turn is connected to the engine block which in turn is grounded to the negative (-) battery terminal - again, I'm not 100% on the original OEM Delco-Remy; and, as you stated you don't know "if" it's the original ALT (so, there's that). At any rate, I think you said you've replaced the ALT twice now? Not sure where this is going relative to an external ALT ground wire if you've already replaced the ALT twice. Did/Do either or both ALTs you replaced have an external GRD lug/post? "If" you elect to use an external GRD wire connected to an ALT lug/post, you can connect that wire to any known good ground source - engine block would be ideal.

 

Realize that you are buying from a store known for the cheapest parts, which while they advertise a “lifetime warranty” to get people to buy their parts, they are “the cheapest parts” and are therefore likely to fail prematurely. I worked in the auto parts industry back in school and learned a lot about not only the auto parts industry, but people’s purchasing habits.

Most auto parts stores have different levels of parts, with the cheapest having only the parts that failed during test being replaced, and the most expensive having every replaceable part replaced no matter if it tested bad or not.

My recommendation is to find a local rebuilder and have them completely rebuild an alternator for you. They will replace every part and not just the parts that test bad on the machine. They typically do this for a price equivalent to the parts store rebuilds.

 

^^That's solid advice.^^

 

I'm going to chime in and just say that I installed the exact same alternator 5 months ago on my '72 Supreme and it has done well.

 

Looks to me like the GND wire has pulled out and vanished. I recall seeing a wire with a ring terminal under a nut on the alternator securing bolt (nut). I would check your CSM. I think you need to get a couple "ring terminals" and a piece of wire, clean and connect GND and a solid ground on the engine or alternator bracket.

 

Refresh all the grounds... at least the major grounds in the charge/start system to include the voltage regulator (VR) ground.
Find an OEM correct unmolested alternator. Get it rebuilt by a professional that uses USA parts.

Verify the VR is in good shape.
Take it to the shop that does the Alt rebuild so they can test both as an assembly. If the VR is in question upgrade to a digital VR. Save the Delco cover on the old one and affix it to the new one if the OEM look is desired. Or sell it to someone looking fer the Delco stamp, don't toss it. It will cover the cost of the digital. VR.

https://www.prorebuilders.com/
Ask for Rick.
They sell VRs too.