Needing advice on an electrical issue that is driving me nuts!

Ok my new Lowrance Ti came in yesterday. I hook up the hot and ground. The hot is a switched hot and ground is on the fuse panel at the top. I verified I am getting a good ground and battery voltage. I run my transducer then go to power on the Ti and it will not power up. I checked the connector and one pin has battery voltage and the other is a good ground. My other unit at the bow is another Lowrance so I hook the Ti up to it and it powers on. My older unit won't power on at the new connection either. I noticed the horn wasn't working a few days ago so I bought a new one and hooked it up but it doesn't work either even though I have battery on one side and ground on the other. So I am thinking the Ti and horn issues are related but what could it be since there is battery and ground at both locations? Oh and both the bow unit and new Ti are powered by the same battery.

Check all fuses.

If a fuse was bad it wouldn't have battery voltage. I am not an electrician by any means but if it has battery voltage and a good geound it (and the horn) should work.

May be a bad (high resistance connection) on either the ground or positive for the new unit. If you use a multimeter, they pull so little current that it can still read fine 12v+. But the instant it is under a real load the voltage drops too much for the unit to run. Try a test light and see how bright it is compared to a check at the fuse box.

It could also be reversed polarity.

That means you have a bad connection somewhere. When no power is needed it will have voltage, and as soon as power is drawn it goes away. The only way to find it is start at beginning or at end with probe while turning unit {or what ever} on. (power before on, Yes?) Power when turned on. Yes? (Power after turned on.Yes?) May take two people to make it easier. Yes they are hard to find when Like that. Watch meter when turning unit on. Any funny business and woot there it is.

I would check the ground connection first and make sure it is getting ground from the same battery as the positive also. 90% of the time my problems are due to the ground side....

Thanks for the advice everyone. I was thinking I could run a temp wire from the neg or pos on the battery (one side at a time) to the unit so I would know if it's a power or ground issue, then go from there. I did see a bunch of ground wires at the top of the fuse panel. If it's a ground issue I could always put a bus bar under the dash and route all the ground wires to it, that's if the problem isn't an easy or obvious fix. I'm gonna tinker with it tonight and will let yall know what I found. Thank's again!

Check resettable breakers

Well I first narrowed it down to voltage. I hooked a wire from the neg directly to the battery. With my meter hooked up voltage would drop from 13 to 6 when I tried to turn on the FF or hit the horn. I pulled the switch panel loose and as I was moving it trying to look for something obvious I noticed a few of the lights on the switch would come on. So I held the horn button while moving the switch panel around and the horn scared the [censored] out of me. So it's either a bad connection on one of the switches or maybe a switch is messed up internally. Gotta get up early for work tomorrow but at least I have it narrowed down. Thanks again everyone!

I would look first at the connection of both the power wire(s) and the ground wire(s) that operate the switch panel. I'd bet one of them is not making the trip as they are right now.

Wayne

You don't need to add a bus bar for GND to fix the issue. You already have the connection points you need; you just have one not making good contact.

The voltage drop you see with the meter when you activate any load at that switch panel is because the boat circuits at that switch panel do NOT have a low-resistance path back to the battery negative (GND as we refer to it). You have one common problem that existed before you installed the new FF, and the FF malfunction is just a further symptom of that issue. You have an open GND circuit that is causing what we refer to as a "Ground Loop" via some alternate but high resistance path. This is why you get some indication of voltage, but it drops as soon as a load is applied. The front unit works fine because it has a different reliable low-resistance path to GND while the circuits at the switch panel do not.

You indicated that the fuse panel you have has a group of GND connections (typically for circuits wired to the fuse panel).. Those grounds should be on a common metal plate. That plate will typically have a stud connection for a wire that goes back to the battery, maybe of a bit larger gauge wire. Somewhere along its path, that connection is compromised. You will find that it is loose or corroded, resulting in no GND for anything connected to GND at that switch panel - note your common problem of horn and FF as evidence of this. It could be you just need to clean a connection and/or tighten one. You're giving evidence of this by the fact that the horn sounded as you moved the switch panel around. The problem isn't with any of the ground connections for individual items at that fuse panel - it's the wire going back to the battery. The problem is even at the fuse panel end of the wire as opposed to the battery end of the wire since it worked briefly just because you were wiggling it around.