1988 Rinker Captiva alternator question

Mrblue4274

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Jul 17, 2014
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Hi, newbie here on my first boat, 1988 Rinker Captiva, with a merc 4.3 v6. The original owner said he'd noticed the voltage gauge had quit working, and thought it might be the alternator. I started it with water muffs on and read 14.5 volts on the battery while running, 12.5v when off. Seems to be charging like it should, but volt gauge still doesn't move. I noticed on the back of the alternator there was a wire that came off a case screw and goes to a little black box marked Mando .5 250v, then a heavier black wire goes from a tab on the black box into the wiring harness. The red wire coming out of the black to the case lug on the alternator is broke off. Does anyone know what this box is for, and if it'd have anything to do with my volt gauge not working. I also noticed the oil pressure gauge doesn't move, it's close to maxed out running or off, and the temp gauge didn't move either. Thanks for any help.
 

alldodge

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Hi, newbie here on my first boat, 1988 Rinker Captiva, with a merc 4.3 v6. The original owner said he'd noticed the voltage gauge had quit working, and thought it might be the alternator. I started it with water muffs on and read 14.5 volts on the battery while running, 12.5v when off. Seems to be charging like it should, but volt gauge still doesn't move. I noticed on the back of the alternator there was a wire that came off a case screw and goes to a little black box marked Mando .5 250v, then a heavier black wire goes from a tab on the black box into the wiring harness. The red wire coming out of the black to the case lug on the alternator is broke off. Does anyone know what this box is for, and if it'd have anything to do with my volt gauge not working. I also noticed the oil pressure gauge doesn't move, it's close to maxed out running or off, and the temp gauge didn't move either. Thanks for any help.

:welcome: to iboats

Could use your engine serial number but it sounds like someone has been messing around with the electrical system. Yes, agree your ALT appears to be working. If you could post a pic of the Mando black box that may help in determining what you have.

All gauges are run off the ignition circuit which becomes hot when the key is turned to run. In the run position, the purple wire becomes hot with power from the battery. If none of the gauges are working it could be the 20amp fuse, that being said most time when the fuse blows the engine will do nothing.
 
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sounds like a condenser. Mando is a brand name so there plenty of info on the net on wiring and parts. I don't think that has anything to do with your gauges. First test is to measure voltage at the gauge. Measure from positive post to negative post then positive to a different negative point as your problem sounds like a bad ground. Oil pressure and temp can act as a ground path if the negative wire has a problem. The gauges normally peg to max when this happens. If you have voltage then you probably need to test all the gauges and see which ones are bad.

may be part# 811879
 
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Mrblue4274

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http://instagram.com/p/qtp_lLxR51/ I determined the box was a fusible link, like the one mounted on the back of this guy . For testing purposes I installed a. .5 A fuse and noticed no change in gauges. To verify someone has definitely been into wiring. I also found the trim gauge not working, but upon inspection of the trim rotor plate I found it to be cracked into pieces, then later found the wires just hanging down by the motor, not hooked up. One thing I did find on the oil sending unit was a pretty crusty wire which I cut back and installed a new ring on. The weird thing about it is I grounded it and it maxed out, installed it onto sender and it stayed zero , slightly cranked motor for a second and pressure jumped up to 40psi, then just kinda stayed there, then when I shut off key it maxed out. I think now I'm battling multiple issues. The temp gauge seems to check out ok, so now I'm thinking maybe thermostat is stuck, no letting it build temp. We'll not sure where to go from here, but thanks for the replies.
 
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I can not see the picture you linked to.

http://www.boatfix.com/merc/Techbk/96/96HGC4.PDF are you sure it was a fuse?. The black box with 0.5 250v written on it should be a 0.5 mfd condenser. if you look at the link i attached theres a exploded diagram of a mando alternator. I presume you are talking about item number 9 which is a small black box with one wire going to the positive post of the alternator.
 

Mrblue4274

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Glenn, your 100% correct. Someone for whatever reason had it connected to ground on the alternator, then connected to a wire in the harness. That wire was a bigger gauge wire and goes into the harness with other alternator wires. My gauge problem I'm beginning to the is related to power backfeed of some sort. The oil pressure gauge requires voltage to move the needle to its max position, and when I shut the key off that's exactly where it goes. Also the aftermarket radio shuts off when the ANC/nav switch is switched to nav, so that's an issue as well, and maybe the source of the voltage feedback. I'll see what I can get figured out tonight , after I get off work. Thanks again for the replies
 

Mrblue4274

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Jul 17, 2014
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Ok , here's where I'm at, back to gauges. I have 12v on the purple wires to all the gauges with key on. If I pull the signal wire off from what I've read, I should read 12v on it, but I'm only reading 8.3v on the oil pressure, 8.2v on the temp, does this seem like the gauges are bad ? My wires ohm out good, and sensors seem to ohm out. Am I correct in the thinking that if I pull the wire off the temp sensor , and measure from it to ground I should be reading 12 v ?
 
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Jul 21, 2014
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Your signal voltages are going to vary, That's how the gauges will be able to have readings other than min/max. If they were dummy lights than yes those usually use an open/closed sending switch. Most of these are variable resistors affected by changing temp, pressure etc and will send higher lower voltages to the gauge. If you had voltage feedback into the gauges I would not hold my breath on them working again - at least properly.
 

Mrblue4274

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Jul 17, 2014
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Ok , I think I've got a handle on it. Originally I found the condenser wired between a black wire out of the wire loom and the alternator case . I traced the black wire to the big plug in on the motor and then traced it up to the main ground under the dash. I'm convinced that the gauges and other lights where pulling there grounds through the devices like the oil sender and water temp gauge. I fixed the temp gauge by grounding the case of the sensor, which it not receiving a ground probably kept it from getting screwed up. The volt gauge however does not move at all, with power connected to it directly from the battery, so it probably fried too. The oil gauge seems to operate properly, the sending unit seems to be the issue there, I disconnect the sensor wire at the sensor and reading goes to zero. I reconnect sensor wire and it stays at zero then start engine and get 40psi on gauge, shut off engine and gauge maxs out, then turn key back on and gauge goes to 40, pull wire off sensor and gauge reads zero. Also at idle or revving engine the gauge just reads 40 psi and has no fluctuation. I believe all issues probably came about from that main ground not being connected, or at least being isolated from ground since for some crazy reason they wired it off the condenser wire, ugh!!!!!!
 
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