S70 How to test Alternator signal wire

roycr · Post by **roycr** » 07 Oct 2018, 13:44

During an accident, my front bumper assembly and all attacked to it where shifted sideways a few inches. Drive train subframe was not affected. Yank bumper back and all works like normal except the alternator. During the wreck the top radiator hose was ripped off at the motor. This most probably means coolant was leaked onto the alternator.
I would just assume it was the alternator, except the dash warning light does not come on with key in on position or with car running. The bulb test good. All other warning lights work. Check engine and service light have gone on and off since I've owned the car so they're no help. Wiring diagram TP3941202 shows an item 24/13c as the only thing between the ignition and the alternator. (except the bulb).
I use the car daily by charging the battery with a charger, so would like to be able to test the alternator in car before removing it. Voltage at alternator is always the same as battery when running and there is no voltage drop on the cables.
My question is would a dead alternator make the dash light not work and is it possible to test it in car other than no change in voltage at the battery. Not really sure what the purpose of the signal wire is.

Post by **misha** » 07 Oct 2018, 15:54

If signal wire isn't attached the alternator will not charge!
It acts like "awakening" for it.

If it doesn't get ON on bulb check then it isn't attached or it have a break somewhere.

Post by **Ozark Lee** » 07 Oct 2018, 17:45

The easy way is to unplug the wire from the alternator and see if the battery light on the instrument cluster lights up. The way the cluster is wired up when the alternator has a problem it lights up nearly every warning light on the cluster along with the battery light.

...Lee

roycr · Post by **roycr** » 08 Oct 2018, 02:27

Thank you both for your quick reply. I will do some more testing tomorrow and let you know.