Electrical Issue - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Mike Massingill · 05-06-2009, 09:35 PM

Just finished rewiring truck, new single wire alternator with built in regulator, new optima battery.

We have a main circuit 30A fuse that blows after driving the truck about 5 minutes. Replace the fuse and drive another 5 minutes. Does not blow while the truck is idling.

We do not feel we have a short, we have traced the wires and the wiring is new.

We feel the fuse is blowing from an overload of maybe 35-40A.

Could this be caused by the atlernator somehow over feeding the circuit?

I will pull the wire to the alt in the AM and drive it to see what it does. If it does not blow what do you recomend to fix it?

Thanks, Mike

**KevsClassics** · 05-07-2009, 12:50 AM

You would need a 80- 100 amp fuse. Best way use at least 8 gauge wire with a fusible link where it connects to bat.

Mike Massingill · 05-07-2009, 09:09 AM

Yep, I think that is the problem.
I will change it out today.

68gmsee · 05-07-2009, 09:23 AM

Before you install a higher fuse check the output voltage. The one wire alternator shouldn't overfeed the circuit it should self regulate to within 13.8 to 14 vdc (+/-). Put a meter between the battery posts see what voltages are being fed to the battery at idle and at higher rpms.

More than likely it's the alternator. From what I've read about single wire alternator, it needs a "feed" to excite it to start regulating and usually gets it from the stators themselves after you crank it. Yours doesn't blow the fuse at lower speeds because it's using battery power at that point. Once you rev it up to higher speeds the transistor gets "excited" and regulates the output.

05-06-2009, 09:35 PM	#1
Mike Massingill Registered User Join Date: Sep 2006 Location: Houston, TX Posts: 28	Electrical Issue Just finished rewiring truck, new single wire alternator with built in regulator, new optima battery. We have a main circuit 30A fuse that blows after driving the truck about 5 minutes. Replace the fuse and drive another 5 minutes. Does not blow while the truck is idling. We do not feel we have a short, we have traced the wires and the wiring is new. We feel the fuse is blowing from an overload of maybe 35-40A. Could this be caused by the atlernator somehow over feeding the circuit? I will pull the wire to the alt in the AM and drive it to see what it does. If it does not blow what do you recomend to fix it? Thanks, Mike

05-07-2009, 12:50 AM	#2
KevsClassics TILT COLUMN GURU Join Date: Dec 2006 Location: FRESNO CA Posts: 4,276	Re: Electrical Issue You would need a 80- 100 amp fuse. Best way use at least 8 gauge wire with a fusible link where it connects to bat. __________________ Instagram kevs_classics64 64 Impala SS Conv 72 Blazer 2wd 75 Jimmy 2wd 63 Belair wagon 02 Silverado ext cab. DD RIP EL JAY Last edited by KevsClassics; 05-07-2009 at 12:51 AM.

05-07-2009, 09:09 AM	#3
Mike Massingill Registered User Join Date: Sep 2006 Location: Houston, TX Posts: 28	Re: Electrical Issue Yep, I think that is the problem. I will change it out today.

05-07-2009, 09:23 AM	#4
68gmsee Active Member Join Date: Jul 2007 Location: Centrally located between Houston, Austin and Waco. BCS area. Posts: 7,947	Re: Electrical Issue Before you install a higher fuse check the output voltage. The one wire alternator shouldn't overfeed the circuit it should self regulate to within 13.8 to 14 vdc (+/-). Put a meter between the battery posts see what voltages are being fed to the battery at idle and at higher rpms. More than likely it's the alternator. From what I've read about single wire alternator, it needs a "feed" to excite it to start regulating and usually gets it from the stators themselves after you crank it. Yours doesn't blow the fuse at lower speeds because it's using battery power at that point. Once you rev it up to higher speeds the transistor gets "excited" and regulates the output.



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