I was stranded on Wednesday night with a weak battery. Fortunately I was only a few miles from home and my wife brought me some cables and we jumped it and made it home. My car is stock with all stock electronics, no add ons.

Symptoms:

Car started right up when I started my milk run

Noticed that the ammeter was hanging below the centerline when I turned on parking lights; was sitting right in the center before.

Tested battery when I got home: 9.78 volts (actually MM said -9.78. Not sure whats up with that)

Charged battery for 4 hours then tested voltage: 12.87 volts

Car started right up, tested voltage with car idling at 1500, all electronics off: 12.42 volts

Swapped alternators with a grapefruit alternator I had on the shelf: Same exact results

Brought first alternator to get tested: Tests good

So, is this my voltage regulator? Can someone give me details on testing the VR?

A few weeks ago my ammeter was running about half way up the plus side. I assumed this was correct because the car has a 50 amp alternator in it.

The next week I noticed my parking lights and headlights were not working. I chased this for a day or two and realized that I popped all my bulbs. Thought this was weird but didnt know why. So I replaced all the lamps and they have been working fine since but the ammeter does not go above the centerline any longer.

I know these issues are hard to chase but any help would be appreciated.

John

Voltage while running should be 13 to 14 volts.

You have a broken Voltage Regulator.

The overcharging you noticed when the bulbs blew was the first issue.

Now it appears to be not permitting a charge condition at all:rolleyes:

The VR is adjustable but in this day and age it is more convenient to replace it with a new part.

The charge voltage should be ~13.6 - 13.8V when the engine is idling.

Extreme - or + readings on the Ammeter are the indications of a fault condition.

I would really doubt the you have the original voltage regulator since it would likely have been replaced in the last 40 years. I say that becuse somewhere along the way, in the part stores, the mechanical adjustable ones were replaced by solid state, non adjustable ones. Moot point since your info points to a bad VR anyway.

I would really doubt the you have the original voltage regulator since it would likely have been replaced in the last 40 years. I say that becuse somewhere along the way, in the part stores, the mechanical adjustable ones were replaced by solid state, non adjustable ones. Moot point since your info points to a bad VR anyway.

Pretty sure it is original or replacement oem. The car only has 50,000 miles on it and was parked long term for 2 periods during its life.

It is adjustable but does appear to be damaged. I did order a replacement. Should be here this afternoon.

Thanks for the tips all. I'll let you know if it works out.

John

Pretty sure it is original or replacement oem.

Yeah, that looks original to me. Many of the 240Zs I have seen still have the original voltage regulators, so I don't think its that unusual. John, you should put the original cover on the replacement you get, so you keep the stock look.

-Mike

Not sure where to go from here. Replaced the Voltage Regulator and still have the same problem.

I am beginning to wonder if I have a wiring problem. Is there anything in the charging circuit that could cause a problem like this? I have already checked the fusible link for continuity and made sure my white/red wires are connected under the dash.

John

I would advise you to have the Charging System checked by a reputable Shop. It may be a simple wiring fault but they will be able to fully diagnose the problem.

OK, so I figured out the problem. After having all the obvious parts tested or replaced I started checking the wiring. Turns out that the W/R wire that runs from the alternator fusible link to the fuse box was not making contact under the dash where the engine bay harness connects to the dash harness. the Female end had broken free of the wire and I could not see this with the large, discolored boot on it. I recrimped the end and my ammeter now shows a good charge. The Nissan alternator on the car right now is 50 amp so I will probably put the 40 amp stock alternator back on and see how that works.

Thanks for all the help.

John

On my 70 240 there are two heavy gauge wires in that location above the passengers right knee. Can't remember if both are W/R but at least one of them is. On my car the vinyl boots covering the tab connectors for those two wires or whatever they are called have black marks (see pic) which seemed to indicate overheating. I don't know what the best procedure for correcting this is. I thought of soldering the wires together bypassing the conenctors or soldering the crimp but instead I scraped the flat connector with a knife to get all the corrosion off and plugged and unplugged the connector many times after using deoxit. Then I packed the connectors with dielectric grease. Replacing the connectors might be good though I could not seem to find any that would accept such large wire. Being an old duffer I wasn't sure I wanted to stand on my ear on the floor of the passenger compartment to solder the crimp with solder falling in my face.

Edited October 7, 201014 yr by Mikes Z car

Yeah, I don't know If I would do that either. Those connections connect the main power to the fuse block from the engine bay. There is not much play there either.

On my car, both wires to the fuse block are W/R. From the engine bay one is W/R and the other is W.

Nice job finding that one! Those are tough to track down.

While this was not your problem, I can tell you that you'd benefit greatly from a newer (slightly larger) alternator with an internal regulator. This is a very common upgrade, costs about $65.00 with the Erwin adaptor plug, and works great-more juice in the system.