I have a 88 7.3, went to Napa and the one for the external regulator was showing 65 AMP. (Maybe Ford rounded up and said 70amp.) The high output ambulance one had different wiring on the back so I did not upgrade. It had to be ordered but they had it there the next AM. Also be sure to check your fusible link to make sure it works. (Charge wire between alternator and battery, but hooks via the batt terminal on starter relay as I recall.) Mine died prior from vibration and rubbing and my truck stopped charging. (Alternator died a year later.)
Also I recommend you spend another $35 and replace your external regulator. (10 minute fix. Take a minute and clean the terminals.) Many links and message boards suggesting not replacing both is a bad idea. Evidently many found the older part caused the new part to die a quick death. Also you will have the peace of mind your overall charging system is now updgraded. When I replaced mine I ended up with a new issues. One of the wires from the regulator connector goes up to a second single connector, then to ground on the fender well. Oddly from moving the regulator the connector between the regulator and fender well moved and now was not allowing a connection. (It was corroded and now that it moved a little it would not make a good connection. I thought my regulator was perhaps bad. It was this random connector mid wire (Not clear why they put it there.) that was no longer making a good connection. So for good measure you might want to clean up your battery terminals, clean up your grounds, and check the fusible link and ALT wires for continuity.
Lastley most towns have a place or two to rebuild Alternators and Starters. If you cannot get something delivered quick see if someone can rebuild it today or tomorrow. Most common issues with those are the brushes as I recall. The new 2000 up ford alternators eat up the stator (? Brass/Copper part the brushes ride on.) shaft and that is a whole different issue to fix.
all this headache is why I suggest moving to a 1 wire GM self exciting delco alternator for $70 or less total ( can get these from salvage yards for $10 or so usually in working order these alternators are tanks and rarely ever fail ) ( can reuse the factory pulley from ford alternator ) and eliminate all the headaches of the external regulator and that rats nest of 30yr old wiring that usually has been hacked up by either previous owner or mice or whatever
I live by the KISS theory ( keep it simple stupid ). The GM 1 wire alternator mod is very simple and cheap / reliable and well easily rebuilt by you if needed on side of road for like $25 in less than 1hr with minimal tools and back on the road again happy days
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Oh and nearly every single auto parts store has the single wire GM alternator in stock 99.9% of time and for cheap the good old 10si / 12si alternator is a legend among construction industry / mining industry / hot rodders / racers / alternative energy industry and farmers for a reason theyre reliable and can be adapted to almost any vehicle/motor with ease and did I mention cheap and many use these in wind mill /hydro power and such they turn these into PMA alternators and use them for alternative power sources and much more.
The big problem for our motors is they don't make quality electronic components for them anymore according to most part manufacturers our engines are end of life and obsolete so the only factories making the electronics anymore are crappy quality and often 2nds and 3rds on the quality scale. This is why most electronics for almost any vehicle from autozone / advance auto parts are crap they buy 2nds and 3rds to get cheaper parts so it costs them less to stock them and they sell them for a premium.
basically tiering refers to quality control lvl as you go up in number the quality drops meaning theyre closer to failing or closer to being out of specifications Napa is mainly a tier 1 parts seller Oreily's auto parts is mainly a tier 1&2 and autozone / advance auto parts are mainly a tier 2&3 parts seller this means the cheaper price your paying is often for a much inferior part closer to failure second you buy it and often are bad when you buy them.
Trust me I had to argue with a customer over a starter took 6 starter swaps to get 1 good 1 ( it failed 1 month later ) I told him to have autozone test them before he brought them to me to install and he did not. I charged him labor for each and every time I had to install / remove the starter ( cadillac north star under the intake alot of labor ) needless to say he wasn't happy with me but he got what he asked for and paid for parts wise.
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to give you a idea how much of a pain it was I did this 6 times because of the customer argued with me and demanded I just put it in saying it was good. I even explained had to tear top of motor apart to change it and he didn't listen I said its a 2-3 hr process each time and he just couldn't understand it needless to say I never wanted to see him ever again I was furious and so was he.
