MG Car Repair: Changed generator, jumper wire, starter solenoid

Question
Howard, have 67mgb, pos ground, recently when running headlights the battery ran down very quick so pulled generator and voltage regulator turns out gen was toast so purchased a new one , shop that checked out both pieces indicated both were now fine ,, installed the new gen and wiring was same as on old one but now when it starts up the amp gauge jumps to negative , I shut it down quick just in case but am baffled what changed could the new gen not be good? I am certain wires went back on regulator correct , any clue for mr.
Please respond to  

Answer
Hi rod,

Here is the test sequence. First put a volt meter across the two batteries or across the two posts if you have a single 12v battery. Read battery voltage. (12v +) leave the volt meter attached and start the engine and hold the idle to 1500 RPM and read the volt meter. It should read between 13.8v to 14.5v but not higher or lower.

If it is lower then you need to test the generator. To do that you need to "Full Field" the generator.

Do this, take a jumper wire of 12 gauge (same size as the large brown wire on the generator) add a clip or clamp on one end or a large female spade connector like the one on the large brown wire and add a short pig tail to that end of a smaller wire (14 gauge) like the one on the field terminal on the generator.

Remove the two wires from the back of the generator and attach your 12 ga jumper wire to the large terminal and the pig tail small wire to the small flat spade terminal (field). Now you have a single 12 ga wire attache to both terminals on the generator. Be sure the jumper wire will reach the starter solenoid (67 MGB had a remote starter solenoid under the hood) One of the large cables on the solenoid is the battery cable and the other is the starter cable.

Hold your jumper wire so it does not contact anything and be sure that the two wires you removed from the generator do not contact anything. Have someone start the engine and set the RPM at 1500. With your voltmeter attached (you can attach the volt meter to that battery cable end at the starter solenoid to read battery voltage)

When the engine is at 1500 touch the end of your jumper to the battery cable on the solenoid and read the voltage. DON'T LEAVE THE JUMPER ON THE CABLE FOR MORE THEN A COUPLE OD SECONDS!!! The voltage should be at or close to 15 volts.

This is a "Full Field" test of the generator and tells if the generator is good. If you don't get 15 volts then the generator has a problem. If you do get 15 volts the next test is for the regulator and /or wiring.

If you get 15v disconnect both the jumper wire and the pig tail from the generator and replace the original wires on to the generator. Now with the voltmeter attached to the battery cable and reading 12v + start the engine and put it at 1500 RPM and read the voltage. If it does not read from 13.8 to 14.5 volts then the regulator or the wiring is bad.

Be sure you belt is tight because a generator is very hard to turn when charging and a slipping belt will cause a low or no charge condition.

Let me know.

Howard