solwyt

Could someone please simplify my life? Ive read and read and everyone seems to be doing different things. I have installed and not wired in a 100 amp 3 wire alternator in my 78 corvette. I have installed but not run the wiring for my dual fans which draw 25 amps each. Someone please tell me what wires I need to switch out and what guages to use. Someone who has actually done it and has had no issues. Wire to battery? Wire to starter? Wire to horn relay? Wire to something else? Just which ones and what guages and i will do it.....

ignatz

FWIW: I have a 100 Amp 3 wire alternator with stock wiring harness in my 69. I run the fans from a relay sourced directly by the positive battery cable, jumped from near the starter motor. Hard to say what the draw is on the alternator when the fans are running as I would guess the regulation is sensitive to battery voltage and I don't know what voltage the positive terminal sits at when the fans are running. The alternator never gets hot. I think that answers a couple of your questions. The horns are as originally wired.

DUB

I have done this.and NO ISSUES but it working perfectly.

I ran a larger gauge wire from the starter over to a custom made junction block. Then the wire from the alternator I also increased the gauge size to what I just used from the starter....just because I felt it could not hurt. I installed a fusible link in the wire that I attached to the starter positive battery cable stud. The fusible link was about 6 inches long and it has to be 4 gauge sizes smaller than the wire I used.

Now the reason I did this was because I also changed how the headlight were wired in and used relays....so that is why I made a junction block. The junction block and be bought.

PM me if you need any specific help...and I can give you my shop phone number so you can call me.

OR...wait for some others to post their thoughts.

I assume you have the wiring and relays for these new electric fans???

And I also assume that you also have some type of switch that will control these fans so they come on when the coolant temp gets to a specific temperature???.

'Richard454' has employed some amazing wiring changes in his build. SO...just to let you know that there are some people otehr than myself who can get you through this.

You horn relay does not good in your year model if you are thinking of wiring something to it.....it is NOT like the early Corvettes.

DUB

mrvette

20 years ago, not knowing much about the new alts.....I installed a 17 SI on my serp drive changeout....108 amps rated, wired like the OEM wimpy style......over the years I swapped out the silly wire to the horn relay across the fender well, and went down the valve cover and to firewall, across and out....8 gauge......the OEM broke and long story....I have DPFI on my car...

so as to the FANS, they draw a steady 25 amps or so, Mine are Dual Spals 11" and I put the control relay on top of the fan shroud, putting the wire from the alt, through a inline fuse and a ten gauge wire to the relay.....computer control wire in same harness, ground to main frame directly beneath the fans.....it's a 30+ amp relay.....

DO NOT run the fan power through the wiring harness and especially off the battery/cable/starter directly....you are then pulling the current from the alt through the main factory harness, and dropping over a volt or so in battery charge...and if you do a bunch of short trips and running a/c the battery is never quite too happy.....as the voltage at the battery will never reach over 12.5 or so, even if the alt is pushing 14v on charge....because in fact the alt regulator is being lied to by the wiring system.....introduced by your going off the battery directly.....



you know, when you wiring a house, say, you playing with 110 volts....you drop say 2 volts off a 20 amp run....so what?? appliances don't notice, power plants vary by more than that, and the % is just that 2% or so.....

you drop 2 volts outta 12 and no one is happy .......especially the battinator......

solwyt

What guage wire did you run from starter over to your block? This sounds like a good option considering im going to be doing all the connections on drivers side from inner wheelwell. Have more room there on that side. That would make things easy togeab power for fans. Also, what size wire should run from alt over to starter? Can i leave the wire from starter to batt alone?

lionelhutz

Dub describes what works perfectly. No need to run wires all the way to the battery or any other nonsense like that. Wire from alternator to terminal block and terminal block to the solenoid. Use 6 gauge wire. Use a 10 gauge fusible link to protect it. You generally want to put wire short circuit protection any time you tap off with a smaller gauge wire so put the fusible link at the starter solenoid.

You could then remove the original wire that goes from the alternator to the firewall connector. In case you didn't know, on a 78 the charging wire goes into one firewall plug and then jumpers to another plug where it exits and goes to the solenoid. You definitely do NOT want to run 100A of charging current through this original circuit. You could leave the original wire too, but it something ever happened to the new wire from the alternator then the charging current would be going through the firewall connectors.

A simple terminal block like this works great as a connection point in a suitable location to tap your fan power or other power from.

https://www.summitracing.com/int/par...-215/overview/

If you want to get fancier then something like this works too. The wires go out between the tabs.

https://www.summitracing.com/int/par...0155/overview/

Street Rat

My new fusible link is blue and says 3.0 mm. Is that ok for 4 ga power wire from alternator / junction to starter? I already have the 4 ga wire to use.

lionelhutz

That sounds like the right size for 4 gauge wire.

DUB

YES...I used 6 gauge wire and got it from a welding supply house close to my shop. I liked it due to the countless strands in it and that the housing was very flexible and I still protected it with some of the sheathing.

DUB

Tampa Jerry

Do a search for Mad Electronics. They have a great Website for upgrading electrical systems for these old cars. Dub and others are correct, the best way to to is to bulk up your main feed wire and add relays. Mad has the kits and instructions. The kits are inexpensive. Good luck. Jerry