Chiltons used to be the #1 with details out the butt.
They were just expensive. These days they are about the same as in fact containing info. Chiltons tend to also cover more then one make model automobile thus making then more expensive.
Nothing beats the GM tech manual though.
I've bought several over the years used off ebay, realy cheap. Just have to make sure they are clean and no torn pages before bidding or buying.
Your Haynes should have the test procedure in the chassis electrical section.