Datsun Roadster Forum-311s.org

Hi everyone,

I'm not very experienced in electrical work and I've hit a dead end. I recently replaced my battery. After reconnecting the new one, I turned the switch to start the car and got exactly one turn of the motor before everything went completely dead - no headlights, horn, signals, etc. Nothing other than swapping the battery - i.e. I didn't disconnect any other wiring.

I did some research on the forum and found many references to the ammeter possibly failing, so I bypassed that. That didn't change anything and I'm kind of stuck given my lack of knowledge / experience w/ electrical issues.

Right now, I get voltage at the fuse box with the key in either the OFF or the ACCESSORY position. As soon as I turn the switch to RUN, voltage to the fuse box drops to .02->.04 volts (not zero). This is a 69 SRL w/ EI in case that matters.

This feels like a short somewhere but I have no idea where to go next in diagnosing the problem. If anyone has ideas I would really appreciate the help! Thanks!

Welcome.
I would probably start with the easy stuff:
Re-check fuses
Check to make sure the battery is actually charged (no, seriously … it happens).
Check terminals/connections for corrosion and tightness.
Check your battery connection at the starter (you may have pulled on the cable a bit hard) and check the solenoid connections while you’re there.
Check all the negative grounds (including the grounding strap at the starter).

Let us know.

PS. Don’t forget to disconnect the battery first before wenching at the starter and solenoid

See if this helps.

http://kendo-usa.org/datsun/datsun_char ... _69_70.pdf

Did you Replace with a new battery? sounds of a weak battery If used
1st trickle charge that battery, then have it load tested free at a parts store , a multimeter is needed to check for voltage drop tests & check charging volts dont assume its one problem of the system , especially on this age car
the solinoid may have contact probs
Any obvious probs need to be addressed

My suggestion is to clean all the battery terminals and cable connections really well as a start.

If this all occurred with just a battery change-no other changes that is your clue.

1) If BOTH of the terminals are not very clean (but do have a high resistance connection), they can conduct enough to read 12V at the FB under no load. but when any significant load is applied, the connection is no longer "good enough" and the voltage to the FB and car goes way down.

2) The new battery can just be tested lots of ways, load tester, jumpstart, etc. but chances are the new battery is fine if you just purchased it from a store.

Try that first before disturbing other things that were working fine before the battery swap. Hope this helps!

2X what JT68 said. I have run into this a few times with my old farm tractors. That load of that one turn of the motor can be all that is left in the poor connection, and at the instant when it fails an arc will jump in the connection. This arc will deposit carbon which insulates the connection. Not just clean and tight but SHINY clean and tight.

Double check your ground.

Most likely 2 things, bad ground due to poor fastening, or you broke a poor connection somehow when moving it. That or a fluke bad battery.

Well, I took your collective advice and really scrubbed the inside of the battery terminals. On the outside they appeared perfectly clean (certainly not any corrosion) but evidently they had enough gunk on the inside to be the culprit.

THANK YOU - THANK YOU - THANK YOU!!!!!!

Happy to help. Glad you got it running!

pcarguy wrote: Fri Nov 19, 2021 4:52 pm Well, I took your collective advice and really scrubbed the inside of the battery terminals. On the outside they appeared perfectly clean (certainly not any corrosion) but evidently they had enough gunk on the inside to be the culprit.

THANK YOU - THANK YOU - THANK YOU!!!!!!

You are welcome! I have cleaned the inside of battery terminals many times and what works best for me is my pocket knife.