Blue Sea ACR Wiring Question

[Tiktaalik]

Thank you everyone for helping to educate me on this topic! I do suspect that the alternator works but it isn’t self exciting. The charge light circuit works (the bulb lights up if grounded). The alternator worked when it was tested at the shop. After it was tested I replaced the regulator with an adjustable one set to 14.7v. I wonder if this change has something to do with it?

Why does the new alternator have two B+ terminals and not just one like my old one? Do these two terminals/wires serve different functions? When I wire up the plug I wired them together as one fat cable. I am wondering if I should get the plug with two separate B+ wires and see if those two need to be connected to two different points in the distribution box? That’s not how they were connected but that doesn’t mean it’s correct. I’m also going to clean and grease my engine/frame/transmission grounds.

I have attached the wiring diagram for my Mercedes 300GD here so you can all have a look. Its the "Starter Control, Power Supply" diagram that we should be looking at. I think the dash charge indicator light circuit has a relay in it. I wonder if that relay is not grounded or has stopped working?

That alternator is probably not self exciting. In which case you need to supply a some voltage through the proper wire for it to start charging. This should be done through the D+ wire (this will be how it was wired from the factory). Usually the instrument cluster has a light which supplies power through the D+. This serves the purpose of exciting the alternator to start charging, and also serves as an indicator light. If the alternator is not charging, this light will see ground on the alternator side, thus illuminating. In some cases the factory light is not sufficient to excite the alternator.

In your case it sounds like the regulator may not be functioning properly.

 

[DaveInDenver]

What do you mean grounding the lamp? The lamp goes between +12V and D+ and should only illuminate when there's a problem, it should be off normally. You could jumper D+ and B+ and it would work, the problem being in that case the field is never de-energized and drains the battery when the engine is not running. That's why D+ is wired from an ignition-hot source, so the field is energized only when the key is on. Are you grounding the D+ side of the lamp with the key on just to prove the bulb isn't burned out?

 

[Tiktaalik]

My alternator guy asked me to unplug the alternator cable from the alternator and ground the blue wire to the case if the alternator. If the light doesn't come on there is an issue with the circuit. If it comes on and stays on there's an issue with the alternator. Thats how I was told to test it. The light turned on and stayed on when I did this but it will not turn on otherwise.

 

[DaveInDenver]

The blue wire could be grounded to test that the bulb and charge indication circuit are working, but the D+ needs to be on the +12V side operating for the field to energize. If you leave D+ connected to ground you would bypass the field winding.

I'd have though the light would illuminate with the key on but the engine not yet running normally.

 

[Tiktaalik]

Got it!

Here's what we're looking at in the distribution box. The blue wire on the bottom right hand side is coming from the alternator. The big pink wire on the right hand side, also from alternator. On the opposite end of the distribution box there are two main harnesses. The top one has 2 red and, one black/red wire and 1 blue wire coming out of it. That harness goes into the firewall. Underneath of that (obscured by the top 4 wires in the photo) is a smaller harness with two wires coming out of it. That harness goes to the positive terminal of the battery. Do these appear to be connected the right way?

The blue wire could be grounded to test that the bulb and charge indication circuit are working, but the D+ needs to be on the +12V side operating for the field to energize. If you leave D+ connected to ground you would bypass the field winding.

I'd have though the light would illuminate with the key on but the engine not yet running normally.

 

[DaveInDenver]

The wire colors might not match, so don't use them as absolute references. Trace or check them against the wiring manual.

 

[Tiktaalik]

Will do but perhaps you can help me interpret this? Take a look at the screenshot of the wiring diagram. It appears that the two B+ wires from the alternator go to different places. One appears to go to a relay and I can't really tell where the other goes. I'm not good at reading wiring diagrams. Where do they go? Also, are all the three connection points in the distribution box three isolated circuit or are they combined? Perhaps this is my issue? Disregarding how the old alt was wired up, perhaps the new one needs two separate B+ wires coming out of it? Currently I only have one B+ wire going into the center connector of the distribution box.

 

[luthj]

Those spade terminals are only good for 30A absolute maximum each. If your old alternator was only 30-40A, then it makes sense that the new alternator will have 2 terminals to carry the extra load. Most alternators use output studs, as they produce too much current for a spade or similar type terminal.

 

[Tiktaalik]

That makes sense. The old alternator was stock but had been rebuilt to 88A. It had studs. The new one with 3 prong plug is rated 55A but actual output tested at 65A.

Those spade terminals are only good for 30A absolute maximum each. If your old alternator was only 30-40A, then it makes sense that the new alternator will have 2 terminals to carry the extra load. Most alternators use output studs, as they produce too much current for a spade or similar type terminal.

 

[Tiktaalik]

I still haven't resolved my alternator issue but I thought I'd share photos of my battery tray mock up for my Mercedes 300GD. Fits two Odyssey 34-1500 batteries with room to spare for Blue Sea Systems ACR, fuses, and Power Posts.

 

[luthj]

Why do you have 2 fuses attached to the ACR? You really should have those fuses mounted at the batteries themselves. Otherwise they serve little purpose on the ACR like that . A single fuse would provide the same protection in that config. Best to protect as much wire as possible.

 

[luthj]

Sure, with good wiring practices you could forgo a fuse. Though I would tend towards having one, just cause I have seen engine compartments pretty mangled, and a fire would be possible due to short.

 

[Tiktaalik]

Thats what I've been wrestling with. I have OJOP Battery Connectors that I want to use for both batteries. I can't use the post mount fuse panels with the OJOP Connectors.

Why do you have 2 fuses attached to the ACR? You really should have those fuses mounted at the batteries themselves. Otherwise they serve little purpose on the ACR like that . A single fuse would provide the same protection in that config. Best to protect as much wire as possible.

 

[Tiktaalik]

I tested the Exciter Circuit this morning. Its the blue wire from the Alternator that is connected to the dash charge indicator light. I've been told this circuit should have 12v when ignition is on or the alternator won't excite a charge. I checked this circuit both at the Distribution block end and at the Alternator end. 1.57v and 1.86v. When I ground the blue wire circuit to the alternator housing I get 12.79v. That tells me something in that circuit is preventing sufficient voltage to reach the alternator to excite a charge.

 

[luthj]

I am not a fan of those connectors. They don't seal the cable end, so moisture can wick under the insulation. I have not used them myself, so I can't comment on longevity. Some versions of the Odyssey batteries come with stainless stud terminals, which would be my preference.