There's that "Oh, Crap!" moment when things are clearly not working. This moment of horrigying clarity is balanced by the utter obscurity of the root cause. After all, I only changed a one simple thing. How could it go so horribly wrong?
A solution is something that must be earned. It's never simply given, and the price is always dear. And often, there's no actual progress, just increased understanding.
That "Oh, Crap!" moment was 2A power bleed. More of a hemorrhage, really; a "drain your battery to useless over the next 4 days" level of bleeding.
Wiser heads at American Diesel Company, Kilmarnock, VA, suggested that's it was the "Oil Pressure Exciter Switch". See the sidebar for details on what this switch is and does.
It turns out that the switch was not actually the culprit.
It turns out that we have a much more obscure problem. We have the "Faulty Isolating Diode" problem. Find a copy of Edgar J. Beyn's The 12 Volt Doctor's Alternator Handbook. On page 104, Beyn adds this information: "a shorted isolating diode by itself would hardly be noticed. Make sure there is no other problem."
I followed the wiser heads at ADC and Beyn's book so that I could be absolutely sure what the problem was. Merely finding this kind of problem has a cost.
The easy way to diagnose this is to remove the alternator from the engine. This is messy and unpleasant. And. If the alternator is good, it means reassembling the engine.
It took some scraping and brushing to clean up the connectors enough to measure a super-low (but non-zero) resistance between one of the diodes and ground. This is the kind of resistance that leads to about 2A current in 12V.
Poseidon Closes a Door and All the Windows, Too
This seems like progress. It isn't, actually. But it starts out feeling like progress.
The blown diode is replaceable. It's a "MO ISOL PLATE-DUAL 1-30 25A". A good automotive electric shop can order one. But.
This old Motorola alternator is really only about 55A of output (at best). Assuming it's only 75% efficient means about 2 hours of run-time to charge the house batteries every single day. That's crazy.
Modern thinking suggests that we should have at least a 100A alternator for our house batteries. That leaves us closer to an hour each day of engine run-time.
ADC carries the Balmar 712-110; a 110A alternator that is designed specifically to replace the old Motorola 8MR that we have. This is often paired with the ARS-5 regulator. Defender, for example, offers the Balmar 7-Series Alternator / Regulator Kit. Defender's price was almost double what ADC asked. Call Brian at 804-435-3107 to get hooked up.
) is a forgiving and loving God; when He closes a door, He opens a window. Poseidon (Ποσειδῶν) is a harsh son-of-a-bitch. When he closes a door, you have to figure out whether or not there's a window you can force open.
What's So Bad About That?
The tricky part about the Lehman installation is the water pump and alternator belt geometry. The belt is threaded through the cooling system. To change belts, you must drain a few gallons of coolant, take the hoses apart, thread in the new belt through the hoses, and then reassemble and recharge the cooling system.
All that to put on the belt.
Wiser heads suggest putting on two belts. The second belt can be cable-tied out of the way. It permits emergency repairs without enjoying the complexity of the Lehman plumbing geometry.
OK. So. Where were we?
Right. Draining coolant before we can add belts before we can install the new alternator before we can install the new regulator before we can be sure we've resolve the electrical problem with the new switches.
The engine coolant drain is a little bitty brass "Angle Bib Drain" fitting thing hidden under the alternator. After removing the alternator, it's easy to see the drain. The drain cock even has a hose barb making it easy to add a hose to drain the anti-freeze into a bucket so that it can be reused.
The little "ears" on the drain cock have cracked and are spinning free.
We need to get a replacement drain cock from ADC. It's clear that when we put the Vise-Grip brand locking pliers on the broken drain cock to open it, it will be mashed into a pulp. Ideally, we can capture the engine coolant and reuse it. Once we've drained the coolant and replaced the drain cock, we can then get back what we were supposed to be doing: dismantling the cooling system so we can can back to what we were supposed to be doing: replacing the belt with a new one and a spare.
After we replace the belts, then we can get back to what we were doing: replacing the alternator. Then we can add a regulator. And be sure that the 2A battery drain problem is actually solved.