#3 "IGN" Fuse keeps blowing.

[blodi]

I've searched and found nothing (with a solution) to my problem.  71 240z...built L28...triple webers....pertronix ignition

Last week I took the car up through the revs and the engine sputtered a bit and my tach and center gauges went dead. This problem came out of no where. Car has been running great and reliably all year. 

I replaced the blown fuse and the gauges came back...it stayed fine until I tried flooring it again and once again at high rpm.... it sputtered and the fuse blew.  

The problem has gotten quickly worse and now the fuse will blow as soon as I turn on the key...without the engine even starting. 

I've tried hooking up a 12v light to the fuse and unplugged everything associated with that fuse...tach, temp, fuel, water, oil press gauges and turn signals. The test light still stays on when I turn the ignition on. 

The only thing that makes my test light go off is when I unplug either the voltage regulator or the t plug on the alternator.   I replaced both of these last year. I tried again replacing the VR.....no change.  I got MSA's fuse box upgrade for good measure...no change. 

Could it be a bad alternator that would cause this even when the engine isn't running?  Like I said, it's only a year old maybe. I did notice that the amp gauge would read a bit high at times then suddenly come back down to a "normal" reading when driving. 

I'm stumped at this point and am about to take it to a auto electric repair place, but figured I'd ask here and see what you guys think. 

Thanks!

[SteveJ]

Are you sure you got an externally regulated alternator when you replaced it last year?

[Zed Head]

Try disconnecting the Pertronix unit.  It could be shorted.  Fits the initial "rev" symptom, I think.

[Mark Maras]

 I think I'd start by looking for a bare wire(s) down by the gas pedal and or throttle linkage. I'm wondering if there's a wire hanging down from under the dash that got the insulation scraped off and was grounding when the gas pedal was floored in the beginning and has gotten worse over a short time. Good luck.

[blodi]

30 minutes ago, SteveJ said:

Are you sure you got an externally regulated alternator when you replaced it last year?

No. It was installed by a shop. I've put a few thousand miles on it though and it's been fine until now. Is there a way to tell if it is internally or externally regulated? 

 

30 minutes ago, Zed Head said:

Try disconnecting the Pertronix unit.  It could be shorted.  Fits the initial "rev" symptom, I think.

Just went and tried. No luck. 

28 minutes ago, Mark Maras said:

 I think I'd start by looking for a bare wire(s) down by the gas pedal and or throttle linkage. I'm wondering if there's a wire hanging down from under the dash that got the insulation scraped off and was grounding when the gas pedal was floored in the beginning and has gotten worse over a short time. Good luck.

Nothing close to the pedal at. It really started as an RPM thing and not a throttle position thing. Good thought though. 

[siteunseen]

I'll vote alternator issue.

Hope it's an easy fix so you can get back to the carbs. I enjoy reading those, lots of info for mine when I get the courage.

[SteveJ]

What is the rated output of the alternator? Is there a part number on the housing?

 

[Zed Head]

I would disconnect the VR and the alternator and see if the short stays.  Then count the horse teeth.  Just kidding SteveJ...  Obscure philosophy reference....

[blodi]

1 hour ago, SteveJ said:

What is the rated output of the alternator? Is there a part number on the housing?

 

Attached pics of the alt.  Hard to get a pic with the coolant hose running right over it. 

42 minutes ago, Zed Head said:

I would disconnect the VR and the alternator and see if the short stays.  Then count the horse teeth.  Just kidding SteveJ...  Obscure philosophy reference....

The light goes out.... or rather I should say really dim....with either the vr or alt or both unplugged. 

[Reptoid Overlords]

Should there be a silver capacitor looking device bolted to one of the holes in the back of the alternator?

[blodi]

9 hours ago, Reptoid Overlords said:

Should there be a silver capacitor looking device bolted to one of the holes in the back of the alternator?

That looks to be only on internal regulated alternators..from what I'm seeing? 

Looks like the alternator I have is a 50 amp?

I'm thinking of upgrading to MSA's 60 amp internally regulated alternator...that would trouble shoot the alternator and VR it seems....

Edited September 19, 2017 by blodi

[gundee]

On 9/19/2017 at 7:21 AM, blodi said:

That looks to be only on internal regulated alternators..from what I'm seeing? 

Looks like the alternator I have is a 50 amp?

I'm thinking of upgrading to MSA's 60 amp internally regulated alternator...that would trouble shoot the alternator and VR it seems....

 

Not sure if you purchased another alt yet. I bought this ZX alt from Advance Auto and used the jumper plug from MSA.

I paid $55.99 for the alternator at the time. It looked nicely rebuilt and has really worked well.  (5 years)