Thread: 10-SI alternator checks good but discharges when in car.

Tweet

Here’s a good article on the 10SI and 12SI alternators: Catalog

Almost all electrical problems are due to dirty or bad battery cable connectors. So before you do anything, make sure the connections are bright and well attached. I always like to go directly to the engine block (for the negative) with a #4 AWG if the battery is in the engine bay or a #2 AWG if the battery is in the trunk. I use a hydraulic crimp tool and a tinned copper or solid copper terminal (number 3 below) at the engine. Again, make sure the cast iron is bright and clean. I also use a star washer between the terminal and the block with a stainless 3/8” bolt and a second star washer – it eliminates all connectivity issues and provides peace of mind. I coat with anti-oxidant (NOCO NCP2 is really good – about $12 for a 4 ounce can with a brush) when everything is tight.

At the battery, I use a direct crimp (number 2 or 4). If you want to use a more traditional connector, number 1 is okay in conjunction with number 3. Again, coat with anti-oxidant.

If you have number 5 type connectors you’re courting trouble.

Several quick tests – make sure to use a digital volt meter.

At a reasonable idle (500-750RPM) measure the voltage at your battery with the engine running. A good alternator will maintain battery voltage between 13.9 and 14.8 volts (14.2 is the optimum). With all accessories turned on, there should be at least 13 volts at the battery.

Another test is to measure between the alternator’s output (BAT) terminal and ground. If voltage reads 13.6–14.6, the alternator is fine.

All SI alternators have an internal regulator. To test (with the engine running) put a small screwdriver into the “D” shaped hole on the back and read the voltage. If the voltage goes up, replace the regulator. If the voltage drops, the alternator is bad.

D&B Electrical make a fantastic one-wire, 105 amp direct replacement for $60 – no brainer.
https://www.dbelectrical.com/product...p-10si-se.html

Let us know what you find.

Best and Happy New Year All!
Glenn