How to test ground/hot on fuse block?

[PDubs]

I'm ready to wire my GPS unit into the fuse block using a fuse tap on an existing ACC switch. It's pretty obvious that I will plug in the hot (red) to the tap but where do I put the ground? Is there a way I can test this with my DMM? The block has all the hot wires from the factory harness plugged in on the left and right sides. The top of the block has multiple available plugs and appears only three or four are used. The bottom of the block has only two prongs, larger than the ones on top.

If it's of any help, the boat is a 99 Baja 272. I wanted to use the fuse tap so I can tie in to an existing ACC switch. In this case, the switch I'm tapping into controls the factory depth meter. I've used the DMM to determine which ACC switch is routed to which fuse, so as long as someone can tell me how to test for ground (possibly the available plugs on the top of the block?), I'm good.

 

[Silvertip]

Re: How to test ground/hot on fuse block?

there are so many ground points under the helm you can't possibly miss them. Every gauge has a ground terminal. If the fuse panel has a ground bus you will find a whole bunch of black wires connected to it and it looks like the spade connections in the lower right corner of the fuse panel below. Those terminals are all connected together (common) and should have one larger black wire that is the ground wire running back to the negative terminal on the battery.

 

[PDubs]

Re: How to test ground/hot on fuse block?

I figured that was the case, however, I didn't see a 1:1 connection of red/black. That is to say, for every red wire, I did not see an equal number of black wires connected to the fuse block. My assumption is that this is due to the factory wiring harness and they spliced them all together to reduce the connections. The colors of the fuse connections at the top portion I described are blue, green, etc; seem to be everything but red.

I'll have to go back and check to see if there is a black wire connecting to the main block somewhere.

 

[Bondo]

Re: How to test ground/hot on fuse block?

I did not see an equal number of black wires connected to the fuse block.

Ayuh,... Probably because most fuse blocks are for the Hot side Only...
Grounds are carried back to the battery with a Different circuit...

 

[Fireman431]

Re: How to test ground/hot on fuse block?

Test light...test light...test light...

Clip to a hot lead and poke the terminals to find a solid ground. Very simple.

 

[Silvertip]

Re: How to test ground/hot on fuse block?

If you look at the picture of the fuse panel, just above and to the left of the ground bus you will see a threaded post. That is the main +12 volt feed from the battery. If connects all of the INPUT sides of the fuses in the block. The spade connector by each fuse position is the OUTPUT or LOAD side of the circuit. You do not connect a bunch of +12 wires together. They should all originate at a fuse panel.

 

[PDubs]

Re: How to test ground/hot on fuse block?

Went tonight and grabbed a picture of the panel, inserted below. I tested by turning on the appropriate ACC switch and figuring out the polarity using the DMM and touching the needle to the fuses. Turns out the entire thing is hot. It's not pictured well, but at the top of the fuse panel is a bunch of leads I could connect. Also, I saw one threaded connection in the top portion towards the middle. Putting the red DMM lead on there and the black lead on the fuse, more or less validated no grounds available. I then poked around everywhere to see if all the exposed tabs (such as those on the bottom) were hot and sure enough, no ground.

Short of bringing a wire from the battery and splicing existing wires, is there anywhere else I can ground? With cars, you could simply wire the ground to a seat bolt connected to the floor of the car. My guess is I cannot do the same here. Maybe I can just tap into the accessory socket ground? I would assume that's routed back to the battery somewhere.

 

[JustJason]

Re: How to test ground/hot on fuse block?

If all your stuff works then there is a ground already run up to the helm, you just haven't found it yet. Is there any kind of buss bar under there?

 

[bruceb58]

Re: How to test ground/hot on fuse block?

The ground bus looks like it is right there in your picture where all those black wires are plugged in.

It does not look like you have any spare fuses there. You have a couple of options. One is to daisy chain from the main power and ground feeds and install another small fuse block or the other is to add a wire with an inline fuse to the power feed connection. You would need to put a ring connector on the end of the wire.

 

[PDubs]

Re: How to test ground/hot on fuse block?

Jason - I haven't found a separate buss bar for ground but maybe it's on the panel and I just didn't locate it yet? I tried various things using the actual 10A fuse as one of the origin points but now that I had a night's rest, maybe I can check again a little more clearly.

Bruce - I don't have any spare fuses and was planning to use a fuse tap. The fuse tap contains two slots for fuses and I figured there was no harm in doing it this way.

During my testing, I noticed that the screw in the middle towards the top (with the yellow tip) is hot. If I'm hearing you guys right, it sounds like I should put the DMM leads (red) on the screw and (black) in the top right corner with the black wire/yellow tip. I assume I can just put it in these two points and see if I get a voltage and if I get nothing, then that can't be ground right? Is there a specific setting I should set the DMM to? I had it on amps when testing the fuse, I'm sure I have to move it to a voltage reading somewhere on the dial.

 

[JustJason]

Re: How to test ground/hot on fuse block?

I assume I can just put it in these two points and see if I get a voltage and if I get nothing, then that can't be ground right? Is there a specific setting I should set the DMM to?

Not trying to give you a hard time or anything man... but it sounds to me that you don't have a handle on basic DC electricity, or how to use a meter. The best advice I can give you is to pick up a book on the subject or enroll in some kind of community college that teaches the class.

PS~Bruce is right, after a closer look the ground buss is on the top of the block.

 

[PDubs]

Re: How to test ground/hot on fuse block?

Jason - No offense taken. I will readily admit to taking the fast track and getting a needle-point DMM to try and get this darn thing installed quickly. I would rather ask stupid questions in hopes to getting expert advice before blowing a $500 piece of electronics. :beer:

 

[JustJason]

Re: How to test ground/hot on fuse block?

I'll give you some step by step instructions to getting your electronics wired up, but first, what brand and model is your meter? I want to google up a picture of it so I can see what you need to set it to.

 

[PDubs]

Re: How to test ground/hot on fuse block?

Thanks Jason, appreciate the online learning. DMM I'm using is GE2524. Picture for your reference:

 

[JustJason]

Re: How to test ground/hot on fuse block?

Okay,
It looks like on your fuse block all the slots are takes, so the first question is, do all those wires actually do anything, or was the boat wired with extras?
You can try turning everything in the boat on, and start pulling fuses 1 by 1 to see what shuts off.
If you find that you have an extra/open slot, you can get your power there. Just disconnect the wire that's on it, add your own from the gps, and fuse it appropriately. That will take care of your power.
Next is your ground, right above the fuses you'll see all the ground wire tabs, are there any open tabs?

Ground is easy enough to test. If your meter leads are not long enough, get some wire at rat shack along with a couple of alligator clips and make up a lead. They are usefull to have when troubleshooting anything, I have a few that I made up in my toolbox.
Ground 1 end of the lead you made up to the battery's negative. Clamp the other end of the lead to the meters negative. Put your meter on the ohms scale (the omega sign) and select the 2000 scale. Hopefully the meter has a finer resolution than that, but what you want to see is a couple of ohms of resistance, hopefully under 1 ohm, but when you add up the resistance of everything + corrosion sometimes you get a couple. If you do, then there is your ground.
I"m not sure if that meter has continuity or not, I don't recognize the symbol to the right of the diode test. But something you can try is to put your meter on that symbol (the one that looks like a DC sine wave) and touch the meter ends together, if your meter beeps/tones, then it has continuity. If it does then repeat the test above, if you have continuity between the batterys negative and those ground tabs then you can ground there.
Hope that helps.

 

[PDubs]

Re: How to test ground/hot on fuse block?

Jason - Thanks for the instructions. The boat is wired with aftermarket extras. We are the second owners, purchased from family. The boat has three ACC switches and the previous owner installed some audio equipment that is routed to the other switches.

For power...
Since I'm out of space, I plan to use a fuse tap for ACC #1 switch. On this switch is only the factory depth meter, so I'm not too concerned with adding additional load on there, especially since fuse tap has two slots for fuses. Wouldn't this be an acceptable method for sourcing power?

For ground...
I'll have to go back there tonight and take a closer look at the upper right corner to see if there are any available tabs open. If I do, then I'll try the continuity test you mentioned below. I attempted to put the meter on that funky symbol and touched the leads but no sound/tone. If there are no tabs available, can I just splice into say, the lighter socket? This is the standard 12V socket same as on cars. It would be a hack job, but it would at least get me some ground.

 

[Silvertip]

Re: How to test ground/hot on fuse block?

You don't even need a meter to tell what is what on this panel. All of the grounds (e.g., the ground bus) is in the upper right corner where all the black wires are. Of course the entire panel is hot -- that's the way it works. See the metal tab sticking out the bottom of the panel (has a half hole in it). If you set the meter to read 12 volts, touch the red lead to that tab and the black lead to the ground bus. I will bet you read 12 volts. That tab is an extension of the 12 volt bus that runs down the middle of the panel and powers the HOT side of all the fuses. The outside of all the fuses constitutes the feed to whatever device that fuse protects. So the solution as to where to get power and ground is right in front of you. Add another small panel with the +12 volt bus fed by the tab, and the ground bus connected to the existing ground bus. You now have 4, 6, 8, or as many extra circuits as you need. Or you can simply attach an in-line fuse to that tab for power and ground at the ground bus. If you look really carfully you should find not one but two threaded posts. One is +12 volts feed to the panel from the battery. The other is the ground wire from the battery.

 

[PDubs]

Re: How to test ground/hot on fuse block?

Went back tonight and did some more testing and as stated from pretty much everyone, the uppermost portion is the ground. I did the ground test after stopping by and picking up the parts from TheShack today. Sure enough, everything is now plugged in and the GPS fires up just fine.

Thanks to everyone for their help and especially Jason for making me learn HOW to use the DMM properly!

 

[JustJason]

Re: How to test ground/hot on fuse block?

Good luck!

 

[smokeonthewater]

Re: How to test ground/hot on fuse block?

.................... if your meter beeps/tones, then it has continuity. .............. if you have continuity between the batterys negative and those ground tabs then you can ground there.

FYI many if not all meters will show continuity between positive and negative so that test is not reliable.... I learned that the hard way years ago after making several connections and burning some wires up...OOPS..... otherwise good info...

Glad you got it worked out