A couple of items I can think of. FMJ cars came with three different alternators. The normal 25 to 78-amp version (used for 98% of all Chrysler cars/trucks – from ’70 to 87).
The 100/114-amp version (used on most police, taxis and some special-order cars) used from early ‘70’s until ‘87.
Note: this is huge and weighs as much as the other three designs combined, weigh.
The ’88-89 had different alternators. A Nippondenso (Denso for short) 90-amp (small but external fan) and a (new) Chrysler design 120-amp. Some people refer to the Denso as a lightweight design (it is by a pound or so). The 120-amp Chrysler design looks more like a GM alternator than anything else. The 120-amp is a lot smaller and lighter than the 100/114-amp design. I “believe” the 120-amp version only came on police vehicles.
’88 on Nippondenso (Denso). Note Chrysler only used 90-amp – but aftermarket has bumped of the amperage to 200-amps.
’88 on Chrysler design (120-amp)
Note: all four use external voltage regulators. A person can fit a large array of alternators onto our vehicles – but not all are externally regulated (which can cause problems).
Both ’88-89 alternator designs use different brackets than the ’76-87 alternator designs. Also, the low amp and high amp versions use different alternator brackets of each year group (so, four different alternator bracket setups).
The next issue is wiring. The 25-78 amp and 90-amp alternators uses an 8-gauge output wire – which is good for about 50-65 amps (at 14 volts)
100/114 amp and 120-amp alternators use a 6-gauge output wire – which is good for about 65-85 amps (at 14 volts).
Now we know how much amperage the wiring can handle – but that is not taking into effect the fusible link attached to each alternator output wire:
The 25-78-amp alternators use a (red) 14-gauge fusible link.
The 90 and 100/114-amp alternators use (black) 12-gauge fusible link.
The 120-amp alternators use (black) 10-gauge fusible link.
I have seen a lot of people install larger alternators on cars, mainly for vehicles with large radio/amplifiers installed, but really, for any reason – but don't attempt to replace the alternator output wire with a wire size to accommodate the alternator (or is fused accordingly).
Because of that, I have seen a lot of melted wiring harness and melted fusible links (and underhood fires).
There is nothing wrong with having a larger output alternator – but please do a little work with the wiring at same time. I don’t want to see anyone’s ride burnt to a crisp, aka: having a “bad day”.
Lastly, after an alternator (or voltage regulator, or wiring harness modification) has been installed – always check battery voltage both at idle and at 2000 RPM.
- Battery voltage should be at 13-13.2 volts, engine off.
- Between 13.5 to 14.8 volts depending on outside temperature when running – and only slightly higher at higher RPM.
If voltage is above 14.8 volts and it’s not freezing outside – then you have an overcharging problem.
That said, if the car fender temperature is -20’F (-30’C) then battery voltage when running, can be as high as 14.9 to 15.8 volts and still be OK.
BudW
