PL510 Tach Needle Bounces, Headlights Flicker on Decell and Using Turn Signals

[D52E]

So I've been chasing this one recently. When driving my 1969 510 at night I see the headlights flicker and tach needle jump at times I when release the throttle. Also, turn signal usage caused headlamps to flicker at times.

 

The solution appears to be adding a ground from the battery to the chasiss. The vehicle only had a battery ground cable going to the side of the engine block (I could not find a ground from the battery to body). its possible the cable on there right now is an aftermarket piece that was put on at some point and the previous owner didnt bother adding a chasiss ground. Also, the engine is not original so it's possible there may have been something forgotten when it was installed.

 

Does anyone know where the battery would be connected to chasiss ground originally?

[datzenmike]

Well first be sure the volt regulator is well bolted down and grounded.

 

Off hand I don't know the exact location for this chassis ground, but most are from the negative post to the nearest bolt ... possibly even the one that mounts the volt regulator to the fender. If there is no little wire available on the negative cable then run a 10 or 12 gauge wire from anywhere on the block or head to the body sheet metal. A fine strand cable is best to handle the flexing of the motor. I think I have seen some from the rear exhaust stud bolt to the firewall. Anything is better than nothing.

 

It could be as simple as a wire from the engine side of a motor mount bolt to the chassis side of the motor mount that jumpers past the rubber isolator.

[rpowell25]

I put a ground cable from a starter bolt to a captured nut on the firewall and a ground to the body from the battery.

 

 

 

 

 

 

 

[D52E]

In the end I did run a short 10ga wire from the neg battery terminal to the bolt that secures the voltage regulator on the right strut tower. It seems to have resolved the original issue as well as helping the horns to work.

 

I think I understand now why throttle input seemed to affect the electrical parts operation. Somehow the chassis grounding path was changing with the torsional movement of the engine. Perhaps the exhaust or engine mounts were providing the marginal ground path so it still worked just enough.

 

I'm hoping someone can definitively tel me what the original chassis ground location is from the factory for my curiosity. Perhaps this information can also help other forum members with weird electrical issues.

[datzenmike]

I (can't believe I'm admitting this) fried two throttle cables on a 521 because the ground was missing. Motor and tranny mounts, leaf springs, shocks and body mounts are all rubber and pretty much insulate the ground strap on the motor from the frame and the body. Except the throttle cable. Like all Datsun owners I didn't have the battery secure and it flipped over and the positive terminal touched the inner fender. Current flowed through the body to the throttle cable, to the carb and to the ground on the head. Probably glowed orange hot before I pulled the battery upright. The heat melted the plastic cover on the throttle cable and it hardened like cement. Could not push down on the throttle. Thinking this was a random event I fixed the cable and three months later did it again. Lesson learned the hard way. Both cables were $15 in '77 money!!!!

 

So if the throttle was causing the lights to dim it's probably because it was the path to ground.

[D52E]

That makes sense now... When i would apply throttle, the cable ends (aftermarket cable) would tension up creating a better connection from engine to body. When i released the throttle, the connection would intermittently go open or high resistance causing the electrical items to flicker.

 

After further studdy of the wiring and Mikes help, I believe the ground wire going from the backside of the alternator case (E terminal) to voltage regulator on shock tower could be the designated chasis ground path originally. When I upgraded to an internally regulated alternator I did not reconnect the ground wire to the alternator case becasue there wasn't a convenient point to bolt it to. New lesson learned...

[banzai510(hainz)]

When I upgraded to an internally regulated alternator I did not reconnect the ground wire to the alternator case becasue there wasn't a convenient point to bolt it to. New lesson learned...

 

Thats it right there.

 

 

The volt reg black wire that goes to strut

and balck batter cable wire to head or use a starter bolt thru trans should be good enough ground.

 

 

adding a extra ground would still be good

[doomdatsun]

when grounding the chassis always use sanding paper to clear the paint until you reach bare metal, the metal would be good, to prevent corrosion spray lithium grease on it,

I (can't believe I'm admitting this) fried two throttle cables on a 521 because the Like all Datsun owners I didn't have the battery secure and it flipped over and the positive terminal touched the inner fender.

 

:rofl: :rofl: :rofl: reminds me of someone :devil: