I've got a 78 k20 that I just bought a winch for. So I went out and bought a new 140 amp alternator. My question is should I just replace the two wires coming off the battery or should I upgrade the smaller one that goes from the alternator to the starter to? Also whats the difference between a 1 wire and a 3 wire alternator?
CK5
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Replacing Battery Cables
- Thread starter BlahBlah
- Start date
As I recall, the highest output alternator offered by the factory in '78 was a whopping 63 amps. 
GM sized the charging wire from the alternator to the starter post accordingly. To keep the charging wire from melting when the new 140 amp alternator goes into full charge mode, you definitely need to increase the size of that wire consierably. 
To handle that much current, you need to use at least a 4 gauge wire.
GM sized the charging wire from the alternator to the starter post accordingly. To keep the charging wire from melting when the new 140 amp alternator goes into full charge mode, you definitely need to increase the size of that wire consierably. To handle that much current, you need to use at least a 4 gauge wire.
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a 3 wire has 3 wires: Big red Hot, exciter (usually white), and hot jumper(post to terminal). 1 wire alternator has only the hot wire going straight to the post on the back. If I were you, id run 4 guage straight to the starter from the alternator, and 2 guage from the batterey to the starter. Also a 2 guage ground to the block from batterey.
just hook the old wire to the junction block on the firewall
84gmcjimmy
1 ton status
hijack:
anyone know the size of alternator that came in a 84 blazer/jimmy from the factory?
hijack off
anyone know the size of alternator that came in a 84 blazer/jimmy from the factory?
hijack off
If it's got a V-belt, then it's most likely a 63 amp model. 
I would remove the old one. The insulation on it has probably seen better days anyway. It gets really brittle down where it passes by the exhaust.BlahBlah said:
4xcrazy
3/4 ton status
thought they had 78 amp models in the 84 some-odd years?
I just did some quick poking around at www.partsamerica.com and found a 78 amp AND a 108 amp unit listed as available for a diesel powered '84 Suburban. The 108 amp unit is listed for under $100. Not a bad upgrade for the V-belt set! 
However, they don't list the 108 amp unit as being available from AC Delco, so perhaps it wasn't a factory option?
However, they don't list the 108 amp unit as being available from AC Delco, so perhaps it wasn't a factory option?
1985_K5_Silverado
1/2 ton status
Not positive about '84, but the optional alternator that's originally was on miy '85 when it rolled out of Flint was the RPO K81 66-amp. Believe it or not, the standard alt on the gasoline models was a 37-amp job! Diesels had the 66 amper as standard equipment.84gmcjimmy said:
84gmcjimmy
1 ton status
1985_K5_Silverado said:
Wow I sure hope mines not a 37 amp one.
driney said:
Theres alot of good info on that site, good post.
