85 FB

Okay, this is an easy to follow write-up for anyone that is wanting to have a stronger alternator in their 1st Gen. Let’s face it, the stock 55-60 amp alternator in our 1st Gens are extremely wimpy, and the S5 (’89-’91) alternator is a nice upgrade at 80 amps. I’m providing this install guide in case anyone is currently slightly confused at how to wire up and install a 2nd Gen’s alternator.

Below, you'll find the photos in order since I do not have a storage space to direct link them. You can click on them one by one to see the progress. I apologize for some of them being blurry, but hopefully you can still see what I've done. If someone is willing to host the photos for an easier view, I'd appreciate it.

First, is a shot of all the items you will need. Please note, the first photo was taken before the install of the alternator, so the pack of washers and the 16 gauge wire is NOT NEEDED.

S5 alternator. Mine is a Duralast from AutoZone, Part # 14639. Cost was $139.99 + $55 core charge.

2x small metal washers. Use these to take up the slack on the small output post, since only part of it is threaded.

2x small plastic washers. Use these washers to separate the metal washers on the output post from the alternator. It took me awhile to realize why the output wire was sparking everytime I went to put it on. The metal washers were grounding out on the alternator.

Dielectric tune-up grease.

Soldering Iron (Optional/Recommended).

Wire cutters/crimpers.

Inline fuse holder w/5 amp fuse. The wire on this is long enough to cover the distance of the S terminal and the output post. I actually cut half of the wire on each side to make a better fit.

Assorted spade connectors. This assortment pack comes with plenty of the three popular gauge size (22-16, 16-14, 12-10) male and female spade connectors. You will be using the last two, which are blue and red in color.
NOTE: For a cleaner install, you can always get the 2nd Gen connector from a junkyard or a parted out car, but for now, this’ll do just fine.

The alternator terminals are clearly labeled as B, S, and L on the back of it, so don’t worry figuring out which one is which. The tall black post is the B Terminal and is for the output wire. Your stock wire will not fit on it, so all you need to do is remove the little black plastic snap-on lid at the base of the post. Behind this cap is a small nut which requires an 8mm socket to remove it.

Step 1: After disconnecting all your old wiring from your old alternator, bolt in your new S5 alternator. The new one bolts right in. My '85 had a spacer with the old alternator so I had no need for washers. Also, the S5 alternator has a nut built into its lower rear ear, so you'll no longer need to use the nut that held on the old alternator.

Step 2: On your old terminal connector, you have two wires: one is white with a black stripe, the other is black with a white stripe. Ignore the black wire with the white stripe, you will NOT be using this again. The white wire with the black stripe is the Alternator Warning Light wire. You will be running this into the L terminal. Simply cut off the old connector and install a new female spade connector onto it. Apply dielectric tune-up grease to the connector and install onto the terminal.
RECOMMENDED: Solder the new connector onto the wire for a secure connection.

NOTE: All 3 different female spade connectors, regardless of their gauge, will fit onto the terminal plug.

Step 3: Run the fuse holder (with a 5 amp fuse) from the S terminal to a constant 12v source. The battery or the B terminal will do just fine. The FC and FD’s had their wire run straight to the battery, but it’s up to you how you want to do it. I just ran the wire to the B terminal (output post) to minimize the amount of wire draping across the engine. On one end, I crimped and soldered a female spade connector onto the terminal and on the other, I crimped and soldered a small terminal ring. Don't forget the dielectric grease.
RECOMMENDED: Solder both ends of the fuse holder's connectors for a secure connection.

Step 4: Connect your old output wire onto the B terminal. Remove the tall black post to fit the wire onto the smaller connection. Just remove the post nut with an 8mm socket. Once the post is off, spread dielectric grease alone the entire output post, and then install the two small plastic washers, followed by the two metal washers. Be sure to also coat the washers in dielectric grease.

Step 5: Reconnect the alternator belt, double-check your connections, start up the car, and check your voltage. If everything was done right, you now have a steady 80 amp alternator powering your car’s electrical system.

In the second to last photo, you'll notice the main output wire is securely fastened onto the output post, along with the fuse holder wire. The last photo shows the built in voltage meter in my radio showing a nice STEADY 14.3 volts. I took my car out for a test drive and was glad to notice that the reading didn't drop below 14, a big welcome compared to my old wimpy alternator.

I hope this helps out anyone wanting to do it, and maybe this'll be stuck in with the FAQ page.

Thanks goes to gsl-se addict for helping me with the install instructions and his suggestion to put this up for anyone else that is wanting to do it.

diabolical1

iTrader: (3)

yeah ... very good writeup. thank you for the time and effort. i agree it should be archived.

drunkclever

Where exactly do you check to make sure your getting 80 amps?

REVHED

80amps is the maximum output but the alternator will only ever put out how much is required of it. That means the sum of all your electrical components (lights, stereo, thermo fans etc.) plus the current required keep the battery charged. I doubt most of the people upgrading their alternators are using even close to the maximum load.

gsl-se addict

iTrader: (3)

Good job on the write-up. Glad you like the alt. +1 for being archived.

REVHEAD is correct. The 80 amps is the maximum rating on the alt. Having an upgraded alt basically gives more ability to keep the battery charged with higher electrical loads. If the stock alt works well, there is no need to upgrade unless you have added an e-fan, lots of stero equipment, and so on. The upgrade is nice to do if you have the old alt going out on you. You can get used S5 alts cheap and have them rebuilt if needed. The upgraded alt may cost about the same as a stock alt, so it makes sense to upgrade. I upgraded when my old alt was going out. I got a used jspec alt and then had rebuilt (had a bad regulator). Total cost was less than $100.

kenn_chan

I thought that the s terminal had to go to a switched 12volt source to keep the battery from draining overnight?

something about how it forms a circuit when the engine is off becasue the diode triode set expects X amount of voltage when there is power to the S terminal????


or was this only for the 3rd gen alternator into a 1st/2nd gen body?

any alternator gurus want to chime in?

kenn

gsl-se addict

iTrader: (3)

Close, Kenn. It is actually the opposite. The L/S regulators (S5 and FD) expect to see 12v at the S terminal at all times. The battery drain issues were from people trying to use both stock alt wires (switched 12v and alt light). If you connect switched 12v to the S, the alt sees 0v at S, but 12.x volts at the output. The alt sees this low voltage at S as a big demand for more output. The alt basically tries to charge at its maximum ability with the engine off. Off course, the alt can't charge with the engine off and this ends up draining the battery over the period of 2 days or so. This isn't good for the alt or the battery. I have seen people even try to install relays and such to keep it from happening. With it wired correctly (like in this write-up) there is no issue. On my SE with the S5 alt, the drain with the car off is about 20 mA (about what an LED typically uses). I believe with it wired incorrectly, the discharge rate is like 1 A or more.

craigw1

this is a great post, def needs archiving.

unfortunately for me i have the alt with an external regulator. Using your guys help i've connected it up similar to the setup here. But because of the regulator there is much more wires around. I've disconnected everything....ran the output cable from B terminal to battery as above, ran a fuse protected wire from S to battery ie not a switched 12V but constant 12V then for L I joined to a wire which i guessed by process of elimination to be alt warning light.

my engine install is not complete yet so i haven't fired up. I have put battery in and wired up and got ignition and all red lights came on and voltmeter on dash gave 12 volt reading....and no smoke, thank God.

but proof will be in the pudding.....when i finally start up and alt light goes out and battery does not drain when I leave car standing for 2 days.

at that point I will post a detailed set of instructions as above with pics.

vipernicus42

iTrader: (4)

Don't forget, you can't connect the S terminal to the "B" terminal, you have to go straight to the battery. The S terminal, as gsl-se addict already mentioned, is what tells the alt's internal regulator how hard the alt should be working to charge. You want it to see the battery's current voltage, not the voltage of the circuit at the B terminal. You've gotta think, if they could have just connected B and S, they would have done it inside the alt.

Easy way to remember, no "BS" when hooking up your alt

Jon