Guys I've been tinkering with the Thunderbeast and I replaced all the Charging system components ie; alt, battery, voltage regulator and I've stll got a problem, the alternator is not charging the battery...or producing enough power to keep the car running when I disconnect the battery, this is a rebuilt alt and I know its very possible that it's bad out of the box. My question is will a bad voltage regulator have the same symptoms as a bad alternator or what symptoms will a bad voltage regulator show?
If you test alternator output, it should show full output before the regulator. If it does, it's the regulator. Have you checked all the grounds and connections for corrosion or bad wires, etc? It's not that uncommon to get a bad rebuild, especially depending on where you purchased it. I remember a chain, now defunct, called Trac Auto that sold a lot of bad electrical rebuilds. I know because I took back 3 alternators until I got my money back and bought it somewhere else. Come to think of it, it was for an '83 LTD I had.
Good point Wes about the alternator, I was just talking to someone yesterday, and they went through 3 alternators, before getting one from somewhere else that actually worked.
Wes I found a few ground connections that were suspect while we were replacing these components and they were fixed. The car is running on the battery only, I went to do a voltage check and as soon as I disconnect positve cable it goes dead. A voltage check with the cable hooked up shows 12 volts but its a little hard to check the output on the alternator if it goes dead when you disconnect the battery. I could put what I know is a good regulator on and if it still goes dead I know its the alternator.
alt With engine off a good battery should read around 12.4-12.8 volts at the terminals. With the engine running a little above idle you should get a reading of 13.2-14.0 at the battery terminals. Another little trick to check the alt while it's running, VERY carefully, take a screw driver and touch the VERY center of the back of the alt. You should have a strong magnetic pull. If not, she ain't puttin out.
You need to do the alternator check with the motor running to check output. Check the voltage at the rear of the alternator. It should be in the 14 volt range. If you are getting full voltage at the alternator, then the regulator may be suspect. The plug in the regulator tends to get cruddy so make sure the connections are clean. Electrical problems are traditionally a mechanic's nightmare. The best way to deal with them is to start simple. Go to the most obvious possible problems and work from there. If all the grounds and wiring are good within the charging system, it leaves the alternator, regulator, and battery as the likely culprits. As to the battery, you'd be surprised how many charging problems lead to deposits on the posts/cable clamps. Also, corrosion travels down the battery cables so they have a finite life. A battery can show a good specific gravity as well as a static charge, but fail a load test which shows bad plates. I just bought a load tester and they can be bought often from $20-$40.
Well yall I relearned a lesson today, never assume the prior owner had replaced a part correctly, turns out the alternator was wired incorrectly by the previous owner, we installed the new one the same way and fried it, when I smelled the third one burning I shut it down and went to the wiring diagram from a mustang manual and sure enough he had put the ground wire on the STA terminal. One of these days I'll practice what I preach. The Thunderchicken is slowly but surely becoming the Thunderbeast...pics to come.
