100 amp ALT upgrade ?
Burning Brakes
Joined: Jul 2009
Posts: 1,238
Likes: 288
From: ESCONDIDO CA
2025 C2 of the Year ('63 and '67) Finalist - Unmodified
C2 of Year Finalist (appearance mods) 2019
I recently read an article about replacement. It recommended an 8 gauge wire for 100 amp alternator.
Team Owner
Joined: Jul 1999
Posts: 65,492
Likes: 230
From: Orange Park Florida
Leave the stock wiring alone, and keep any increased loads to be taken off the new alt. directly with it's own wire, NOT run through the wiring harness .....all else including running any power amps off the battery is not to be done, you can run a PREAMP/control device off the battery direct, just be sure you turn the damn thing off.....
or put in an ignition sw controlled relay to the +12 battery source.....
or put in an ignition sw controlled relay to the +12 battery source.....
Le Mans Master
Joined: Oct 2010
Posts: 6,930
Likes: 845
From: melbourne florida
2023 C3 of the Year Finalist - Modified
i ran my upgraded wiring for my headlights directly off the alternator through relays. i also ran an extra larger wire from the alternator to the starter and it works very well.
Le Mans Master
Joined: Oct 2007
Posts: 7,445
Likes: 971
From: Tennessee/Rhode Island
Leave the stock wiring alone, and keep any increased loads to be taken off the new alt. directly with it's own wire, NOT run through the wiring harness .....all else including running any power amps off the battery is not to be done, you can run a PREAMP/control device off the battery direct, just be sure you turn the damn thing off.....
or put in an ignition sw controlled relay to the +12 battery source.....
or put in an ignition sw controlled relay to the +12 battery source.....
Unless you are running extreme amperage draw directly off the battery (which you should not if you can avoid it), there is no wiring change necessary. Of course, running a thicker wire from the alternator to the starter is a nice upgrade, if you are inclined to take on the task. I put 4 Hella Euro Halogen headlights (55/60 watt lows, 100 watt highs) on my 78 in 1990 with a 100 amp 12 SI alternator and ran the relays and wiring direct to the alternator-no other changes to the stock amperage draw. That alternator worked OK (12Si high amp alternators are not great at providing high amp output at idle and the Stock housing does not adequately cool the alternator at high amp output) until I switched in 2009 to one of GM's best modern alternators, the CS-144 140 amp stock output, primarily for the high amperage output at idle, not that I needed 140 amps. The CS-144 charges like a champ at idle, runs cool, and provides more amperage output at idle than the OEM alternator put out (63 amps) at full capacity, and fits right in where the old 12Si alternator sat-paid $169 brand new. I have not touched the stock wiring to the starter and the wiring never gets hot at first start or with all accessories running. Hope that helps!
Last edited by jb78L-82; Apr 4, 2015 at 07:38 AM.
Melting Slicks
Joined: Oct 2006
Posts: 2,417
Likes: 336
From: Texas
i did the same as 7t9l82, my elec. cooling fans / headlights run directly off the alt. (cs130) through relays. i also paralleled a 10 ga. wire from the alt. following the oem charging wire to the starter + lug. i did this for the times when the engine is hot and you turn the key on, engine not running, and the 2 cooling fans come on, backfeeding power through the oem charging wire to the alt. lug and fans or if i forget and leave the headlights or DRL s on also or both.
Last edited by speedreed8; Apr 4, 2015 at 04:23 PM.
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Drifting
Joined: Apr 2008
Posts: 1,305
Likes: 2
From: Lewisburg WV
Unless you are running extreme amperage draw directly off the battery (which you should not if you can avoid it), there is no wiring change necessary. Of course, running a thicker wire from the alternator to the starter is a nice upgrade, if you are inclined to take on the task. I put 4 Hella Euro Halogen headlights (55/60 watt lows, 100 watt highs) on my 78 in 1990 with a 100 amp 12 SI alternator and ran the relays and wiring direct to the alternator-no other changes to the stock amperage draw. That alternator worked OK (12Si high amp alternators are not great at providing high amp output at idle and the Stock housing does not adequately cool the alternator at high amp output) until I switched in 2009 to one of GM's best modern alternators, the CS-144 140 amp stock output, primarily for the high amperage output at idle, not that I needed 140 amps. The CS-144 charges like a champ at idle, runs cool, and provides more amperage output at idle than the OEM alternator put out (63 amps) at full capacity, and fits right in where the old 12Si alternator sat-paid $169 brand new. I have not touched the stock wiring to the starter and the wiring never gets hot at first start or with all accessories running. Hope that helps!
Burning Brakes
Joined: Aug 2008
Posts: 845
Likes: 12
From: LAKE BARRINGTON IL
I agree with upgrading the wires that are involved in the charging process or handling the extra load. You got alot of good advice.
I recently did a 100amp upgrade on my 69...with all the wires invovled, and did the headlight upgrade and radiator fans...so I have fuses there too.
as explained to me...you are upgrading a system that was supposed to handle 63AMP max, thus the GAUGE of wiring used is to support that flow. Moving upwards in AMP will require thicker/lower GAUGE wiring to allow proper flow of electric and minimize resistance. THUS, each level of GAUGE is intended for a certain AMP. google it.
search for my thread...I did pics too. Tony at CE auto electric knows his stuff. tell him corvette Ron sent you...(i get nothing, but he will know the package)
good luck!
R
I recently did a 100amp upgrade on my 69...with all the wires invovled, and did the headlight upgrade and radiator fans...so I have fuses there too.
as explained to me...you are upgrading a system that was supposed to handle 63AMP max, thus the GAUGE of wiring used is to support that flow. Moving upwards in AMP will require thicker/lower GAUGE wiring to allow proper flow of electric and minimize resistance. THUS, each level of GAUGE is intended for a certain AMP. google it.
search for my thread...I did pics too. Tony at CE auto electric knows his stuff. tell him corvette Ron sent you...(i get nothing, but he will know the package)
good luck!
R
Race Director
Joined: Apr 2007
Posts: 11,150
Likes: 890
From: South Western Ontario
The proper way to do this upgrade is by replacing the wires between the alternator and the starter solenoid. 8 gauge would be the minimum size to use.
I assume you're adding more electrical load? I'd run the wire from the alternator to a terminal block and then from the terminal block to the solenoid. Use the terminal block to power the new loads. Also, jumper a 10 gauge wire from the terminal block to the horn relay to power the horns and the under dash harness.
I assume you're adding more electrical load? I'd run the wire from the alternator to a terminal block and then from the terminal block to the solenoid. Use the terminal block to power the new loads. Also, jumper a 10 gauge wire from the terminal block to the horn relay to power the horns and the under dash harness.
Thread Starter
Instructor
Joined: Dec 2007
Posts: 246
Likes: 2
From: colonia New jeresy
thanks for the info i now have a msd 6al box and a amp. the amp is direct to the battery. i still have the stock alt. if i add ele fans i think the alt will need to be upgraded ?