I'm working on a boat for a friend, but this question is not really boat specific. When I take the key to the "On" position, it applies 12v DC to a purple wire, which then supplies all of the instruments with power, and goes back to the motor to supply the coil. I had a ground to neagtive on this circuit, and would up unplugging all the instruments and gauges to find it. Turned out to be the light for the speedometer. Now, my problem is this: When I start plugging the gauges back in, I get big voltage drops in the circuit. For example, if I just plug in the ammeter, I get a 5 volt drop in the circuit. There's no ground in the ammeter, I verified this with a meter. But whenever any one gauge is plugged in, I get large, some up to 10v, voltage drops. Anyone have any idea? Please...

 

I can help. Please send me a wire diagram and where do you take the voltaje readings.

 

First thing: check the obvious. The battery may be dead, or very near dead and even a small load will cause it to drop voltage. I'd definately check that first since the short most likely discharged the battery. Bad batteries will still show 12 V, but then when loaded drop drastically.

Secondly, if you did charge the battery, can you check each meter while it is wired to a different battery (that you are certain is good) to see how they behave on it?

Try these and I'll think about it some more and see what I can come up with for potential problems. Let me know how it works out.

 

I'm gonna have to make copies of the wiring diagrams, as they are in a book and I have a single sheet feed scanner. It may take a day or two, but I will get them. I appreciate you taking the time to respond.


Benny, I know that battery is good, it came out of my boat that I use at least once a week. I will jumper each meter to the battery individually, that is a goo idea... Any other ideas, please let me know...

 

If this is an I/O then you still could have a short on that circuit on the other side of the breaker or even before the switch, or even a bad connection in the breaker.

Is this a fiberglass boat?

Is it an I/O or O/B?

I'm not the best person to ask, I have electrical gremlins in my boat I am trying to chase them down too. But I can help with trouble shooting ideas.

 

It's an I/O, a '94 3.0L Mercruiser with an Alpha Outdrive. And it's a fiberglass boat. I've disconnected everything from that circuit. I seperated the wiring harness at the engine. It electrically seperates the dash wiring and engine harness. I found one short on the engine side of this circuit that was in the electric choke. I'm working on trying to get my scanner working, if I can, I'll unstable the book and try to scan the schematics. I've done a lot of electrical work, hell I'm a Electronics Technician on a submarine, and I haven't had anything kick me a$$ like this before...

 

Yea fiberglass creates a wonderful situation for shorts and lack of grounds. Then combined with a decade of, I'm sure other peoples hacking attempts.

There is probably a 90% chance that the voltage drop is due to the ground. Use a pair of jumper cables, clamp the ground on the battery and run it up under the dash. The ground wire on each gauge will be ran just like the power, in parallel from one to the other. Clamp it on the ground of the gauge and see what happens. If voltage is stable with direct ground, then start checking the ground on each gauge.

I personaly got tired of that and ran an 8ga wire straight from the battery to a grounding block, mounted the grounding block to the boat under the dash and grounded everything under the dash to that.

 

Any luck fixing it yet?

 

No, my wife managed to crash my computer, so I've spent all night rebuilding it... Plus it's to the point where I'm just gonna walk away before I do something that I'll regret, such as get pissed and rip out every shred of wire in that boat, and then re-do. That's crossed my mind several times...

 

Boy that sounds familiar....we'd better not work on a project together...we might end up torching the boat and rebuilding the whole dang thing.

 

See, the minute you brought up torching the thing, I'd be saying, no that's the easy way out. Let's haul it back in the woods and see if a .357 really will go through an engine block... Then, I'd get hold of some C-4, and tell the dude, sorry, I was playing with the ignition trying to get it to spark, and I guess that gas wasn't as old as you thought...

 

That'd be more fun I just usually don't think that far ahead when I throw my temper tantrums. My latest victim was a shower door. It didn't want to go in and I wanted it to go in. Dang that aluminum bent way to easy....

 

Bigger Hammer, BIGGER HAMMER!

 

Yeah, my kids thought it would be funny to lock me out one day when I went out for a smoke... They wouldn't unlock the door, so they got a 'small' spanking, and I ended up replacing a door frame...:o But I was very dissapointed to learn how easy it was to kick in... One medium powered kick and the wooden frame shattered around the deadbolt. So the new frame has a few strategically place iron straps....

 

Here are the wiring diagrams. I know the quality isn't that great, but it's the best I could find.