Join Date: Dec 2001
Location: Belleville, Illinois
Thanked 22 Times in 17 Posts
Test on alternator sense line source
Today I decided to wire in a new plug for the alternator, but first I wanted to check the difference in connecting the sense line to the alternator output versus connecting it to the solenoid.
I hooked a 16-gauge jumper to the sense line spade on the alternator and connected the other end to the alternator output post. It took about two minutes after startup for the voltage at the battery to stabilize and the ammeter to show no significant charge. Battery voltage: 14.58.
Then I shut the engine off, moved the jumper to the main lug on the solenoid, and restarted the engine. After a couple of minutes the ammeter was showing no measurable charge, and the voltage at the battery had stabilized at 14.57.
Then I spliced the new connector onto the sense and excite lines and plugged it in. This time the voltage stabilized at 14.56.
As I suspected there is no significant difference in where the alternator gets its sense voltage as long as there is no great power draw. When there is only a couple of amps flowing from the alternator to the battery, the voltage difference between one end of the output wire and the other is miniscule.
For this test there was no power draw except for the parking brake warning LED (50 milliamps I think) and of course the ignition system. The battery taking a couple of minutes to recharge after an easy start is normal in my experience with this vehicle.
On the other hand, if the alternator is cranking hard there might be a significant voltaqe drop in the output wire, and getting the sense from closer to the battery might make the alternator try a little harder.