I had a funny and slightly embarassing incident a week ago. My cousin has a 1970 Chevy Malibu ragtop that I replaced the engine in 14-15 yrs ago. It lives in a garage and only comes out for summer drives, probably only about 1000 miles on the rebuilt engine. So my Cuz asked me to come over to see and fix a no-start condition.
IT had a fresh battery fully charged to about 12.7 volts. A new starter as well, but no sign of response with a turn of the key. So we hemmed and hawed over it, I checked the fuse box the fuses had corrosion and only showed a bit over 8 volts...? Even w/ a fully charged newer battery the car was electrically dead.
The battery terminals looked perfect batt. cables were excellent too. No corrosion at all... Tried direct hot wiring the starter solonoid, still nothing. Thinking it was a bad starter or solonoid, we proceeded to spend several hours pulling the header and starter, then connecting the solonoid hot terminal direct and grounding the case- and click goes the solonoid!
Ok so we reinstall starter and header after I scrupulously cleaned the block metal for a good ground to the starter...and AGAIN nothing from the solonoid or starter. Then- I noticed a short thin stud at the front of the starter winding case. On a hunch I had my Cuz feed a 12 guage wire w/ alligator clips on it down to me. I clipped on to the thin stud and had Cuz ground the other end to batt. neg. terminal--and CLICK goes the starter solonoid!!
So- I removed the batt. neg cable from the battery terminal and cleaned it even though it looked fine. Re-connected it and it cranked and started!
I tell ya the battery posts and cables looked PERFECT, but there was enough oxidation on the neg. post and ground cable terminal to cause a 4 volt voltage drop!
So I got to learn about bad grounds and re-learned about voltage Drops all over again. Boy did we have a good laugh over this, and my cuz and wife fed me a real nice steak dinner for resuscitating the Cruiser! How to turn a 5 min. job into a full afternoon of wrenching!!
Dr Jacobs said in his book- "By 4 to 1 most electrical problems are caused by bad Grounds."