Hi Everyone, Recently I have had Very strange problems with the alternator , I purchased a new alternator, had them check it( it was perfect) took it home and hooked it up and nothing !! no output at the rear terminal, so I took it back, they checked it again and it was putting out 14.3 volts.I took it home, hooked it up and NOTHING. So before I went crazy I started checking all of the wiring, I noticed that there are 5 red wires on the pos post of the battery, I decided to clean up the connections. I can not find any info that describes what these are for (other than the main cable going to the starter). Can someone tell me what these are for and also any guesses on my alternator problem. Thanks for any help, Bill

 

the other red wires, 2 go to the 'positive terminal' which is tucked up under the dashboard, and provides power to all sorts of electrical systems in the car. another goes to the headlight 'stepper relay', another goes to the radiator fan relay, and another goes to the 'radio suppression relay' which powers the fuel injectors.

when the alternator is hooked up, and you turn on your ignition, does the "ALT' or 'BATT' light come on? does this light go off when you start the car? if it does, thats normally an indication things are correct. if it doesn't come on before starting the car, the alternator won't work.

 

if the alt light is behaving well, next test is to check the grounding, using a volt meter. set the meter for a DC volt scale (if it has manual range, choose a scale with 1 or 2 decimal places rather than autoranging). start the car.

measure the voltage from the battery GROUND (-) terminal to the body of the alternator or its ground screw. this should be quite close to zero volts. if its closer to 12V, you have a ground problem. if its zero volts (or less than about 0.2V) then your grounds are good, skip the rest of this post.

if it was closer to 12V, then check the voltage from the battery (-) ground to the engine ground at the fuel rail... this should again be close to zero. if its not, then your battery ground cable, or the engine block ground cable has a bad connection.

if the batt to engine ground was bad, check from batt(-) to the chassis (I use the metal bracket that supports the power steering reservoir and diagnostic jack). if this is above 0.1V, measure from the chassis to the engine block grounds at the fuel rail, that will tell you if its the battery-chassis cable, or the chassis to engine block.

if batt to engine ground is good, check the voltage from the alternator body or ground screw to the engine grounds near the fuel rail. this also should be close to zero volts, if its closer to 12V, then its the engine-alternator ground cable thats bad. on my 740T, thats connected to the hanger bracket on the front top left side of the motor, its a light blue wire.

oh, each of these ground places, make sure you scrape off any dirt and oxide, so your volt meter probes are contacting bare shiny metal.