Hooked up battery backwards for a sec... now tach& trim ga working eraticall

Just as the title says I have an OMC tach on an 83 115 Evinrude that was working fine. I recently gave the boat a complete once over and decided on a new deep cycle battery but the posts are BOTH 5/16" where the battery i was switching out from had one 3/8" and one 5/16" and the cables coresponded. Unfortunately I did not notice this difference before I hooked up the battery for just a second or two backwards and since then my tach either doesn't work or reads all off seldom showing more than 2000 RPM and the trim gauge sits static until you reach halfway up and it then just immediately rises to full.<br /><br /> This is very annoying and before I start buying new parts i would like to hear what you guys figure I fried or damaged so I know where to start. I wonder if it is the gauges or if I roasted something else in the equation? Its the fact that BOTH gauges are working eratic that has me wondering. These are the only two gauges I have BTW. The engine runs fine and the lights work and radio is fine and no fuses that I have found were blown so? I am stumped any help would be greatly appreciated. Thanks.

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Is your charging system working? Often a polarity reversal will burn up the alternator bridge rectifier and/ or regulator.

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Sounds like you toasted the rectifier. It only takes an instant of reverse polarity.

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

You probably shorted the diodes in the rectifier. Test the rectifier according to the book.

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

I'm not really sure if the charging system is working but I would have to think so. I have run the boat for considerable time since swapping the battery and would be surprised I made it this far with no charging but who knows. The thing that really got me is the trim gauge too... even if its not running it does not work properly. These are OEM OMC gauges and the tach is plugged into the control at the factory plug. <br /><br /> Got two votes for the rectifier so I will order one and try that. Will the tach work okay again provided thats the problem? I have no book to accord too sadly. Thanks guys

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

As others have said your problem with your tachometer is probably due to a blown rectifier. However, this would most likely not be the problem with your trim gauge. When the leads were reversed 12vdc was put on the grounded trim sender wire and damaged either the sender or the gauge. My guess is the sender. The following should help with troubleshooting it. Trim Gauge Troubleshooting

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Don't replace the rectifier before testing it. This is just a waste of money. With the engine running, measure the voltage across the battery. You should have between 13 and 14.5 volts with the throttle advanced to a fast idle.If less, then there is something wrong with the charging system. Rectifiers aren't hard to test with a meter.

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Right on thanks guys. I ordered a new rectifier so lets hope thats it re the tach. I'll check out the sender as those instructions spec out and see whats what there. Gotta love boats!! ( or should I say gotta laugh at half drunken fools who hook up batteries backwards ) lol Thanks again

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Whoa talk about timing. Posted that as I posted mine. Anyways its not real easy to run the boat in my garage without going through the hassle of moving everything to hook up the water and the rectifier is cheap so I really hope thats it. I did look at the rectifier closely and the wires look fine but the bakelite ( whatever that goop is they are glued in with ) is all cracked around the perimeter does that matter or signify its end?

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

Re: Hooked up battery backwards for a sec... now tach& trim ga working erati

The cracking is probably due to the heat caused by it burning up. That's a common tell-tale sign