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Old 25-11-2016, 15:58   #1
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Location of ground wire - Volvo Penta MD7A

Hi all,

I'm new to the forum and happy to start digging into some articles here!

We have an older monohull / Albin Ballad with a Volvo Penta MD7A engine in it. I'm about to dig into a project of removing the fuel pump (potentially) and some other routine maintenance. However, I'm new to working on boat engines. I have limited experience with BMW motorcycles and Toyota Landcruisers and finding that there's a LOT that I'm unfamiliar with on this engine. I've got a good advisor on this project, but it's via phone and email.

I'm trying to locate the ground wire and cut all power to the engine so that I can begin the process of cleaning it to start working on it. I can't seem to find the ground wire (and i'm terrified of batteries). How can I cut all power to the engine?

The battery bank is in the v-berth and is clearly labeled. It's a set of 3 batteries daisy chained together. I can follow the negative terminal (perhaps) to where it connects to the starter but haven't gotten that far. How are where are these things grounded? I know I'm looking for a large gauge wire going that's serving as the ground, but where / how?

We're in a bit of a situation where we can't find a mechanic who will work on this boat, so I'm going to have to roll up my sleeves and use my limited knowledge to perform some simple tasks on this Jurassic engine.

Thanks in advance for any pointers!
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Old 25-11-2016, 17:11   #2
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Re: Location of ground wire - Volvo Penta MD7A

Generally the negative will be connected to the engine via a bolt on the engine mounts or possible the bell housing. On many boats the engine is the ground point. That's been the case with the two boats I've had.

Some boats have a dedicated ground point, that is not the engine. But you should see a fairly large wire 2,1 O or OO, bolted somewhere around the engine.

If you have a battery switch turning the switch to off should disconnect the + side. You only need one side isolated to prevent the sparks from flying. Some boats have a second battery switch to disconnect the ground.
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Old 25-11-2016, 17:21   #3
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Re: Location of ground wire - Volvo Penta MD7A

The positive wire (it's more properly called a "cable" because of its size) will go to the starter and the negative cable will usually go to a bolt on the engine block itself. Both will be fairly large, unlike any other wires connected to the engine.

If you're planning on doing any significant work on this engine you should find a shop or repair manual and the location of the negative cable will be shown in the manual.
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Old 25-11-2016, 17:44   #4
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Re: Location of ground wire - Volvo Penta MD7A

I suggest that you use your smart phone camera to document every detail of your project (and boat). You can post them with questions... here and get a better response. It's also use when you take apart and then re assemble. These pics can serve as a reference library whether you are on or off the boat.... even for ordering parts. You can often take pics of things that are hard to see because you can stick the phone where your head can't go!
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Old 26-11-2016, 08:57   #5
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Re: Location of ground wire - Volvo Penta MD7A

One of the nice features of the MD7A is that it is all mechanical except for the starter, but even that isn't necessary because it is possible to use the hand crank to get it going.

Look on the port aft side of the engine, near the starter motor. Should be a good sized black cable connected to the engine block with a bolt.

The Alternator B+ wire probably runs from the alternator to the starter and connects to the battery bank through the starter cable.

Remove the Negative cable from the battery and then follow the cable to the engine block.
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Old 26-11-2016, 09:38   #6
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Re: Location of ground wire - Volvo Penta MD7A

Welcome.

None of us was born a boat electrician. We learned. Nothing to be terrified about. Just be prudent, and learn. We all did.

This may help:


Electrical Systems 101 Electrical Systems 101
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Old 26-11-2016, 10:19   #7
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Re: Location of ground wire - Volvo Penta MD7A

Hi Stu,

Thanks for the encouragement. I've been reading and watching videos a ton on electrical systems. I'll take a peek at this link as well. It goes to a Catalina forum. Didn't see a mention of electrical 101 but I'll keep poking!
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Old 26-11-2016, 15:20   #8
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Re: Location of ground wire - Volvo Penta MD7A

removing the ground wire from the engine certainly isn't going to unpower the engine. it'll have grounds from many sources including the water. you need to cut the pos at the battery. you could remove the pos cable from the engine but then you have a live cable hanging next to the metal engine.

if you don't under stand your batteries, switches, and how to use a volt meter to confirm if you still have power or not. then you probably shoudln't be playing with it
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