For all you electrical Whizzes out there!
 

Seems I've done something interesting. I replaced the MSD box in my car a couple of weeks ago and since then, I've noticed that the Voltmeter needle is pegged when the iginition is on. I was poking around today and found out that both sides of the alternator and both sides of the coil are open to the valve covers. Presumably, that means that they are shorted to ground.

I've pulled the connector from the voltage regulator and that isn't shorted anywhere. So I'm stumped. Any suggestions?:confused:

Dan, re-check all the work and wiring done with the replacement of the MSD box. I assume it was OK before the changing of the box.

Mike

They would be open to ground.

Think about the points system your MSD replaces. One side of the coil to +12v the other is ground closure from the points.

It sounds like the voltage regulator is sending full excitation voltage to the field terminal on the Alt. So it's either a bad regulator or there is a bad ground connection to the regulator.

The voltage regulator will have up to five connections:

1: Power sense (to measure vehicle 12v).

2: Field coil in alternator (to vary output of alternator to load).

3: Trouble light out, normally supplies ground to alternator trouble light on dash. (this can be opposite supplying 12v on fail, depends on system)

4: Ignition (turn on/off output).

5: Ground.

Sounds like the ground is lifted at the regulator to me... Your alternator gets it's ground through the housing.

electric
 

The valve covers are sometimes not a good ground to use for testing purposes.
use the engine block.
try your test with the key on as well as off.
make sure the cases for the MSD and voltage regulator are grounded.

Checked with the key off and the cutoff switch in the disconnect postion. Everything is properly grounded. I think Ronbo hit the answer. I disconnected the voltage regulator and rechecked the continuity. There was no continuity to the valve covers with the VR disconnected. I'm going to get a new voltage regulator today and try it. I'll let you know how it shakes.

Okay. That's not it. I replaced the voltage regulator. NO change. I've checked with the Voltage Reg, alternator, coil, distributor all disconnected and it still pegs the volt meter. I haven't got a trace of an idea left. Any suggestions besides rewiring the whole car?

Did you have an MSD ignition in the car before?

Are the MSD wires to the coil the only thing going to the coil? Are they crossed?
MSD box has one constant power and one switched power. Maybe one got crossed with the positive output that should go to the coil?

The field coil will be referanced either to +12v or Gnd. From your input you have a single field connection. There were also isolated field alternators like the old GM units that had a "F" and "R" terminal.

You can check this by seeing if there is continuity to the output terminal (field is tied internally to +12v) or continuity to ground. (field is tied to case internally)

This will tell you what you would see from the reg output. (either a pull to + or pull to gnd to excite field coil)

You can verify the alternator (although it sounds like it's working) by disconnecting the field from the harness and putting a jumper on and touch it to +12 and gnd. to verify output. once you know this "bias" you know what the regulator should be putting out. **Warning do this briefly as when you slam full voltage across the field the v belt will likely start screaming under the load.**

Sorry this is so vauge but it's been some time since I delt with a external regulator system and they weren't real consistant among mfg's.

Is this the standard four terminal unit? (with case being gnd. conection)

I'll see if I can find some online references and look at mine to get a pin-out and what you should see. Also try a jumper wire from the block to the reg case to verify the wire harness isn't the culprit.

Actually I just re-read your posts.

Your seeing a pegged voltmeter (on the dash) with the motor not running or alternator disconnected? This says to me your dash gauge is bad.

You aren't running dual batteries by chance? (possibly been re-wired in series instead of paralell)

Do you have a multimeter you can check vehicle voltage with?

Well, the strangest thing. I changed out the voltmeter and suddenly the alternator is putting out less charge than it should. I'm going to resolve this the old way. I'm calling a mechanic to come and rewire the car to use an interally regulated alternator. Hopefully that will solve the problem.

Thanks for everyone's help.

Ya that's probably a good idea at this point. Sounds like multiple problems or mis-wiring.

Except for nostalgia, external regulators are just an annoyance you don't need. Most of the auto mfgs. dumped them through the 70's with good reason.

The old GM internal reg alternator is tough to beat for reliability. I converted a couple of my old Chevys to these to get rid of the relay-based regulators they used.

Sorry, I wasn't more help to you. This stuff can be a little tough to diagnose without being there.

Ron, you were lots of help. You offered suggestions. Oh, and I have a clue for you. It's tough to diagnose the problems even when you are here..

Thanks for the help.

Check the earth on the MSD box is attached and grounded.

What ever you do get r done before Sat.

If I don't get er done before Saturday, can Linda and I ride with you and Judy? We'll ride in the backseat..

You got it.

Just a warning to any reading through this thread.

If you use either a external regulator or internal reg alternator make sure to connect the sense lead to a point as close to the battery as possible. (more importantly away from the output terminal of the alternator)

There's an important reason for this: The lead wire from the alternator will drop some voltage depending on size between it and the load. The battery is the critical component here so it's best to sense voltage right at the battery or off the heavy gauge wire to the starter.

For example if the alternator is supplying 60 amps and the lead wire is .01 ohms resistance then there would be .6 volts drop across the wire. IE: 13.8v at the battery but 14.4v at the alternator.

Use a good stout 8ga wire to the starter battery lug for alternator output. The sense lead is usually fairly high impedance so a 12 ga. wire sould be fine here. In the case of 100 amp use about 4 ga wire. Fine strand preferable in either case. (32 strand or higher)

The regulator won't charge the battery properly if it's getting bad readings from the sense lead so this is very important to battery life.

Well, the problem is solved. Ahren from Ultimate Automotive Diagnostics came over and we went through it and through it and finally found the issue. There is plug that goes through the firewall that has/had four bayonet style fittings. One of the plugs had somehow broken one of the bayonet fittings. Sometimes when the wire was flexed just right, you got continuity. Sometimes you didn't. (Bet you'd never guess that the wire with the busted bayonet fitting was the power wire from the alternator, would you?) It was very confusing for a while and almost... not quite.... but almost rated the R245 solution. Anyway, now my generator charges, my lites work, and I'm a happy camper again and headed to Bartlett Lake on Saturday with the rest of the club. Thank you Ahren. THey guy is a wizard..

Dan,

Send that info about the shop to Mr Pink. He can add it to our growing list of service providers.

Mike

That's a good idea Mike, but Ahren is already listed there. The guy knows his business and the price is generally excellent. If you want someone working on your vehicle that is anal about doing things right, he's your man.