Datsun Roadster Forum-311s.org

OK roadster guru's, I need a little technical help from the collective group. My car is an all original 1967 SPL311. My ammeter has always read between -3 and +5 ish depending on RPM and load on the system.
Yesterday after I serviced the car I went for a drive and started smelling something, looking and my ammeter it was pegged at +30. The car was running fine but I turned and came home ASAP. Popped the hood and I guess during servicing I pushed the pigtail harness between the alternator and the voltage regulator close to the cooling fins on the alternator. The effect was a severely melted pigtail harness. I figured, no big deal. Didn't see any other melted wires or damage, car runs fine just appears to be over drawing amps. I have all the correct wiring, connectors etc. so made a new harness. Plugged it in and went for a drive. At idle my ammeter still reads +2 and with a rev above 1000 rpm it quickly goes to +30. If I turn on lights, heater motor I can get it down to about +8 at a high rev.
Went home, charged the battery which tested viable. Inspected alternator, tightened the ground and hot wires, brushes etc. Still the same +30 above 1000 rpm. Borrowed a spare voltage regulator and tested again. Still +30 above 1000 rpm with no power load on the system.

What am I missing? Any ideas and suggestions are appreciated.

Measure the battery voltage while the ammeter is in the 30A range. If the voltage is below about 14v, you probably have a bad battery, if higher either you mid-connected the new wiring or possibly the alternator is bad (or your new, borrowed regulator is bad).

Alternator & battery can be tested out of the car @ most auto parts stores.

Peace,
Pat

Just for grins, disconnect the regulator @ see if the problem is the same.

Peace,
Pat

regulator is what keeps the amperage down.

you could also check for AC voltage @ the battery to see how the diodes are doing.

you may still have a short somewhere after the melt fiasco.

Thank you Pat and cbez for ideas. I unplugged the regulator and with a rev could only get ammeter to -2???

Will also try another battery tomorrow.

Anything else come to mind? Auto electric issues are not my strength. I'd rather go to the dentist vs trouble shoot electrical lol

Duralast VR728 works fine as a regulator.

what does the voltage read at the battery stopped and running? does it climb significantly when revved?

ps at this amperage you are close to burning out your gauge or damaging more wiring. I would suggest a temporary 35A fuse or self resetting breaker temporarily while you figure it out.

One thing that you did not miss but that you "cooked up" is that the cooling air out of the alternator melted wire insulation. This is not possible. The air is no where near hot enough. The melting had to have been caused by a severe overdraw, most likely a short. When I took my '67 for its first short drive after two years working on it, as soon as it got up to 1500 RPMs it died. This turned out to be caused a wiring work-around by the PO to solve another problem which I had only partially corrected in re-stalling the wiring harness. It just took some slogging through and tracing out using the excellent wiring diagrams supplied here by Curtis.

+30 amps is a good thing , it's charging very good /well
( Which isn't usually the case on these old cars stock )
If it's charging the battery , is the alt singing belt slipping a bit ? Yes ,check voltage turn on headlines, wipers blower mtr , bet it drops way down or if not it's false reading
the voltage reg will charge FULL THROTTLE
( Guy Fieri ) until the VR coil pulls the contacts apart , Ocillating , on off on off , but if the wiring to it has a weak connection
It can do that, check grounding ohms to the VR ,or add redundant grounds
Most parts stores us a amp clamp to read amp output go have it tested , if voltage output is low it will Boost amps

You have a voltage regulator that has failed! Do not run the car until you replace it and check the large white wire for heat damage to the insulation. You could have a real nice electrical fire if you keep running it.

As has been noted numerous times there is NO fuse to protect your charging circuit except the now very expensive fusible link called your ammeter. If you fry the wire that comes from the ammeter to the alternator it will take several wires with it. Also the wire coming from the starter can do the same. Stock alternator is only 25 amps unless you've changed it. Either way not protecting the circuit with a fuse somewhere is a gamble which you may lose badly at some point.

Frankly with what I have seen I might even take out the stock ammeter and use an aftermarket one until you know sure. A bit of a pain to get to though. Many have put a fuse right at the alternator since it is very easy to do.

First take Premo's advice and think about a fuse somewhere. I build in safety fuses for everyone that wants a stock type harness in the driver foot well so you can access it but don't see it unless you want to crawl in there.

Curtis wrote: Tue Feb 08, 2022 11:38 am As has been noted numerous times there is NO fuse to protect your charging circuit except the now very expensive fusible link called your ammeter. If you fry the wire that comes from the ammeter to the alternator it will take several wires with it. Also the wire coming from the starter can do the same. Stock alternator is only 25 amps unless you've changed it. Either way not protecting the circuit with a fuse somewhere is a gamble which you may lose badly at some point.

Frankly with what I have seen I might even take out the stock ammeter and use an aftermarket one until you know sure. A bit of a pain to get to though. Many have put a fuse right at the alternator since it is very easy to do.

First take Premo's advice and think about a fuse somewhere. I build in safety fuses for everyone that wants a stock type harness in the driver foot well so you can access it but don't see it unless you want to crawl in there.

Curtis I bought some 8 Gauge ATC Blade In-Line Fuse Holders a while back to protect my circuits as you and others have outlined. I believe 8 gauge handles up to 40 amps and should be good? What size fuse would you recommend 30, 35? (stock alternator)

Thanks

Thanks

Myself on a 25 amp alternator I would not use higher than 35 and most likely I would use 30. I have an ato fuse box in my car and a 50 amp Nissan alternator. I have a 40 amp main fuse in the fuse box.

Thanks for the ideas and ways to protect the wiring/ammeter during testing. I do appreciate all the suggestions. I had a 4:00 am sit up in bed "oh crap" I'd like to clear up first with someone who has a stock SPL311 in thier garage.


Just so we all are on the same page. The issue started when the alternator to voltage regulator wiring pigtail rubbed up against alternator cooling fins. This caused the wires to be exposed and cooked the harness.

The harness was in pretty bad condition and now I wonder "did I get the new wires in the harness in the correct positions"?
I am going to attempt to attach a drawing of my wire placement with hopes someone with a stock SPL311 can verify my wiring order.

Thank you ahead of time to someone who can verify or clear up the wiring placement on this pigtail harness.

Paging Dr. Curtis to the operating room... Dr. Curtis...

Okay, okay Greg. Here you go, just made it.

Wire positions as viewed from the front of the plug.

http://www.kendo-usa.org/datsun/alternatorplugs.pdf