Alternator and horn relay wiring
#1
Alternator and horn relay wiring
‘70 Cutlass, 350, no a/c... Every wire under the hood has been cut and attached incorrectly somewhere, and I’m trying to fix it.
I have two red wires coming from the firewall towards the battery - a heavy gauge (10-12?) red w/black stripe, and a lighter gauge (14-16). I cannot find the red/black on a schematic. For sure, this is not the pink/black that goes to the relay. P.O. had the heavier going to the (incorrect) horn relay, and the lighter one going to the alternator. I think both should go to the horn relay stud and a new wire should run from the stud to the alternator. I also think that the heavier gauge should have a fusible link wire. Can anyone help me straighten this out?
I have two red wires coming from the firewall towards the battery - a heavy gauge (10-12?) red w/black stripe, and a lighter gauge (14-16). I cannot find the red/black on a schematic. For sure, this is not the pink/black that goes to the relay. P.O. had the heavier going to the (incorrect) horn relay, and the lighter one going to the alternator. I think both should go to the horn relay stud and a new wire should run from the stud to the alternator. I also think that the heavier gauge should have a fusible link wire. Can anyone help me straighten this out?
#2
There should be 4 red wires to the horn relay power stud. 1 from the bulkhead connector (has the fusible link at the stud), 1 from the battery, 1 from the alt, and 1 from the voltage reg. Trace the red/blk wire back to see where its coming from. You may have an aftermarket harness in yours.
#3
There should be 4 red wires to the horn relay power stud. 1 from the bulkhead connector (has the fusible link at the stud), 1 from the battery, 1 from the alt, and 1 from the voltage reg. Trace the red/blk wire back to see where its coming from. You may have an aftermarket harness in yours.
#5
Here is a pic of the red/black wire coming from the firewall. Why it is different, I don’t know - but I ran it to the power stud on the horn relay.
I think I have everything in the right place along the fender and across to the alternator now. Firewall and starter is tomorrow. I’ve never seen such a wreck of a wiring job - who knows what this car has been through since 1970....
I think I have everything in the right place along the fender and across to the alternator now. Firewall and starter is tomorrow. I’ve never seen such a wreck of a wiring job - who knows what this car has been through since 1970....
#7
Thanks, Bill - after unwrapping the rear harness to the regulator and such, I found such a mess of cut wires that I just ordered a full new wire set for under the hood. If you think the output wire here looks small, you should have seen what was there. I thought I was doing much better by increasing it to this size... It's all coming out and the proper is going in. Thanks for the heads up on this - it sent me in the right direction.
#8
Wire to alternator size
I'm not sure what size your alternator is but this table will help you decide what wire size to use. http://www.usawire-cable.com/pdfs/nec%20ampacities.pdf. In the event my link won't post, just look up "amperage wire size table" and you'll find plenty of references. You're gonna be shocked at how big the wire needs to be for those moments when your alternator is maxed out. I'm going to run multiple smaller conductor wires to achieve the same effect as one big one (again, tables available for figuring this out). Since I'm going with all kinds of extra electronic goodies (FI, pump, electric fans, rear defrost, alarm, windows, locks, blah blah blah), I'm going with a much more stout than factory alternator (125 or more amps). Are you adding any electronic extra goodies now or at any time in the future?
I'd immediately either "add to" or replace the factory or replacement harness alternator wire based on calculated requirements...
I'm now concerned that a standard v-belt won't do well under heavy load and my understanding is that serpentines on the 350 olds platform are not practical or worse, non-existent. hmm, maybe it's time for an LS motor... anyone want to buy an FI unit? ahh, there I go dreaming again.
btw, I re-wired my brother's 72 Cutlass that happened to have a partial 71 harness.. which of course is different enough to cause lots of issues at the firewall connection point. I layed under that dash a lot more than I want to admit. The diagrams from the Olds manuals were priceless (both years)! My own "interpolation" diagrams became my gospel because we ended up with a "Frankenstein".
I'd immediately either "add to" or replace the factory or replacement harness alternator wire based on calculated requirements...
I'm now concerned that a standard v-belt won't do well under heavy load and my understanding is that serpentines on the 350 olds platform are not practical or worse, non-existent. hmm, maybe it's time for an LS motor... anyone want to buy an FI unit? ahh, there I go dreaming again.
btw, I re-wired my brother's 72 Cutlass that happened to have a partial 71 harness.. which of course is different enough to cause lots of issues at the firewall connection point. I layed under that dash a lot more than I want to admit. The diagrams from the Olds manuals were priceless (both years)! My own "interpolation" diagrams became my gospel because we ended up with a "Frankenstein".
Last edited by GammaFlat; December 10th, 2017 at 06:29 PM.
#9
I'm only running a 55A alternator - I have very few accessories. I may add an amp for the stereo at a later date. But I see what you mean about beefing up that cable from the alternator to the relay. Is this table telling me to use an 8 gauge wire for the 55? The wire that was on the car when I got it was 18 gauge And I think I sorted out the under dash wiring the other night - but I won't know for sure until the new harnesses get here and they get installed. What an insane mess this car is. There just isn't any single wire that someone hasn't hacked or moved or removed or tapped....
#10
I'm only running a 55A alternator - I have very few accessories. I may add an amp for the stereo at a later date. But I see what you mean about beefing up that cable from the alternator to the relay. Is this table telling me to use an 8 gauge wire for the 55? The wire that was on the car when I got it was 18 gauge And I think I sorted out the under dash wiring the other night - but I won't know for sure until the new harnesses get here and they get installed. What an insane mess this car is. There just isn't any single wire that someone hasn't hacked or moved or removed or tapped....
..but again, I'll be running a lot of high draw stuff and I don't want my daughter calling me from the side of the road .
So, yes, I think 8 gauge would be ample for your application. I'm not sure how yours is wired exactly but if your alternator goes to the horn relay terminal, you'll also need an 8 gauge from your battery to the terminal to ensure enough capacity for instances when you have a lot of electrical load with no alternator support (car not running, belt broke or slipping or alternator dead, and lots of accessories on). I understand this isn't likely but it is what I'd do. We have to assume there may be failures and you don't want one failure to cause others (cascading event - under hood fire).
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