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Turns out you were right, the black alternator wire is indeed 8ga. I just measured it and the outer diameter is 0.213"

Good to know I can follow what you guys have been saying and learn from it. You could very well be correct. The Service Manual is very sporadic about the MB300 chassis cab...it was primarily written for the regular B-vans. Since it makes no mention of the 100A voltage regulator that's in my...

If I ran a 8ga. wire, along with a 12 gauge fusible link, from my alternator output stud to my starter relay stud, this should make bypassing the bulkhead connector no longer necessary, right? If I've correctly understood everything you guys have schooled me on, since electricity follows the...

Correct. Yes, the alternator charges the chassis cab battery and a wire runs from the chassis cab battery to the 12v switched battery isolator solenoid, which allows the coach/house batteries to be charged, but only when the engine is running. Everything in the coach uses 12V, water pump...

Point taken, thanks. I can't wait to start taking long trips with it. BTW, where are you at in Idaho? I'm in Nampa. Click For Full-Size Image.

When I started taking the motorhome apart two years ago, I made sure to keep all of the parts I took off. When I reinstalled the engine, I converted over to a dual pulley setup, because I used a Mopar A/C compressor from a 1983 B150. I also took the alternator and the rest of the dual pulleys...

I'm retired, so I'm always interested in reading articles/posts that will increase my knowledge, provided the info is accurate. Sometimes I feel like a monkey doing math in Greek, when I read technical articles (especially when it comes to electrical...I can read a schematic, thanks to my Dad...

Yep, and the guy who takes credit for inventing that TFI conversion goes by the screen name of JeepHammer. Very long-winded guy. His heart is in the right place, but his info is just outdated and some of it is dead wrong.

That isolator is a solenoid....its official name is "Battery Isolator Solenoid". The only thing I don't know is what amp rating my isolator solenoid is. I think it's 90A but I wouldn't bet a nut on it. And you are correct, the solenoid is, for lack of a better word, "dumb". With 12V switched...

Yeah, I tend to think outloud, to make sure I'm on the right track. The Chassis Cab does indeed have an isolator....it's in one of the pics I posted. I tend to keep what the original engineers designed....I still run the original Prestolite ignition system on my CJ-5 and have had ZERO issues. If...

I can, but only to a certain degree. Unfortunately, the MB300 is often overlooked in the Mopar Service Manual....the '74-'77 Parts Catalog is a better, but the people selling them online are very proud of them. But having the correct Voltage Regulator matched to the alternator does play into...

Quick addendum....my Service Manual only lists regulator P/N 3438150...mine is 3755850 (no mention of it in the Service Manual), with a date code of 235 (2-6JUN75), so I know it's the original. My regulator, when I Googled it, is for 100 Amp alternators, so apparently the Warren Plant built...

And it would make perfect sense to keep the ammeter but for one thing....since it is a motorhome, I do want to upgrade the alternator. There were four alternators available on the B-Vans, 41 Amp. (Red Tag), 50 Amp. (Green Tag) and two different 60 Amp. (Blue & Natural Tags)....no idea what the...

Yep, my fusible link going to the bulkhead connector from the battery looks like yours, except that it's red. Yeah, it does. Accidentally grounding the circuit activates the electrical flow, much like when my dumbass German Shepherd bites the garden hose and water starts pissing out of the...

Nope, it's just two wires with a connector. No idea why they have it like that, but the factory must have had a reason. I think I'm misunderstanding you. How can it be hot but have no flow. What I understand as "hot" means that, when you put a test light on it, it lights up or, when you put a...

So I was completely talking out of my fourth point of contact about that fused wire....it isn't, and I'm surprised because I thought I knew this chassis cab inside and out. What I thought was a fuse holder is actually just a factory connector. Click For Full-Size Image. Click For Full-Size...

I don't know either...my first thought was maybe it's there, in case the something happens to the solenoid, like the 12V power source spikes. I really have no idea. As it stands in stock form now, the ammeter is on full time...will it hurt the voltmeter, if it stays on full time? If so, I can...

Or I think I can skip connecting the 10ga. black wire with the fusible link to the starter relay and, instead, run it directly to the Coach/House battery charging solenoid, like the picture below. I think this will be a cleaner setup.

So, final electrical schematic design, and it looks like we have a winner. My Dad was an electrical engineer at Westinghouse, and he taught me enough to be dangerous, LOL! Click For Full-Size Image.

So this sounds like the following drawing would be the way I need to go, since I would need a fusible link to protect the feed to the coach/house battery charging solenoid. Click For Full-Size Image.

So I would want a setup like this then? I redrew the MAD drawing you posted, to reflect the alternator wire running through the bulkhead connector. Click For Full-Size Image.

What is the preferred method for getting rid of the ammeter and replacing with a voltmeter? Is there a way to limit the resistance in the power feed? Yeah, sorry, they are bulkhead connectors. I'm still on my first cup of coffee. The old fusible link insulation was still pliable...the wires...

It was actually a Mopar part, added to the chassis cab at the Warren Truck Plant. Some chassis cabs got it, some didn't. I don't remember the option code off the top of my head, but it was definitely a Mopar option. Since I plan on doing the MAD bypass, would it matter where in the wiring I put...

You're correct, that is the IVR routing, but mine steps it down to 5V, per my service manual. Here's a different angle of the circuit board, before I cleaned up the copper with BarKeeper's Friend. on edit: I just took a look at my service manual again....that circuit breaker on the back of the...

I need to thank all of you for this thread. While I don't own an A Body (or any other letter Body for that matter), I do own a 1975 MB300 Class C motorhome. I've been restoring it for the past two years, and we're at the point where we can take day trips in it now. We took it out today and the...