Gps and radio turn off when starting engine

[mmiela]

Not all the time but once in a while if I don’t turn the key all the way to the start the engine. When it happens the key might go back to run and have to turn it to start. That is when the radio and gps go off and reboot. Almost like there is a low voltage or something when it happens. Very intermittent.

Thoughts?

 

[seasick]

Yes, it is a low voltage issue. Assuming it didn't always happen, and that you haven;t added additional electrical load to the you need to check the following:
General battery condition and voltage
Inspect and clean battery cable connections (more common cause)
Inspect and clean if necessary, battery switch connections (it could be a bad battery switch also
Inspect and clean cable connections at fuse block/bus bar)
Ground connections are as important as 12v feeds

Since both radio and GPS reset, the issue is in the common wiring.
Start at the battery cables and battery connections, especially any cables connected at the battery grounds that are not the big fat ones .

 

[mmiela]

Thanks I’ll check those things.

 

[Fishtales]

All good points I. Above post. I had the same issue ended up being a voltage sensitive digital sounder.
Maybe set your battery switches to both and then each bank for starting. Might help isolate if a battery issue.

 

[Halfhitch]

On a previous boat I had two Group 24 batteries. If I had only one battery selected it would cause my Garmin to shut down. If the switch was on "Both" then it would never happen. I checked connections till I was blue in the face and finally decided it was just a combination of small batteries and a sensitive instrument.

 

[seasick]

On a previous boat I had two Group 24 batteries. If I had only one battery selected it would cause my Garmin to shut down. If the switch was on "Both" then it would never happen. I checked connections till I was blue in the face and finally decided it was just a combination of small batteries and a sensitive instrument.

I think this is easy to explain. If you are not up to speed on electrical DC theory, it may be a bit confusing.

All cables, connectors, witches and the like have some resistance. When a current is drawn,there is a voltage drop that equal to the current times the resistance. In general for battery cables and switches, the resistance is quite small. So when small currents are applied, the voltage drop is small.
When you start the motor, the current is large, 100 amps or more is possible.
In your boat, when two batteries were selected, the GPS didn't restart but it did when one battery was selected. In the first instance, the voltage drop was not large enough to cause an issue but one one battery it was. Why? On two batteries, the current draw is split between two cables, one from each battery to the switch. The voltage drop between the battery and the switch was half ( assuming same condition of batteries and cables) of the drop that occurred when one battery was selected. Your accessories feed off a point after the two lengths of battery cables meet ( at the switch).
Your voltage drop on one battery is greater than on two batteries and happened to be large enough to cause the plotter to restart.
In all likelihood, larger gauge cables would have eliminated the issue.