Low voltage at dash volt meter and at ignition terminal on the ignition switch....

[Lou C]

This has been a more or less chronic problem on my '88 Four Winns with OMC I/O. The dash gauge will read low when I turn the key to the ignition position and the dash gauge reads 10-11 Volts. If I hook up a digital volt meter positive terminal to the ignition terminal on the switch and the other to the return terminal (ground) on the fuse box I get the same thing. However, when I hook up the volt meter pos terminal to the batt terminal on the ig switch, I get battery volts. It seems like I am losing voltage somewhere in the dash wiring, but I can't figure out how the current flows through the switch, gauges and dash accessories like the blower and bilge pump.

With the engine running the batteries read 14.3-14.4 V so its not an alt problem, it's a dash wiring problem. I looked in my OMC shop manual and the F/W dash wiring schematic. F/Ws way of wiring it different than OMCs (even though F/W was owned by OMC when this boat was built) and the F/W schematic is very difficult to read. It looks to me like there are several junction connectors where there could be corrosion but I am reluctant to try to pull these apart due to the age of the wiring and possibility of damaging the pins inside. The boat starts, runs but you can tell the dash wiring voltage is low because the blower runs slower than it used to. At first I thought it was just an old voltmeter with corrosion internally but as it turns out the old voltmeter is reading exactly the same as the digitial voltmeter when hooked up to the ignition terminal....with the engine running, the voltemeter reads about 2 volts low, vs what I have at the batteries.

Thoughts.....like where to start.....

In the past, I also had a no ignition issue that I traced to oxidation in the old fuse box and the old metal/glass fuses. I do have battery voltage at the fuse box though. I wish Painless Wiring made harnesses for boats like they do for muscle cars!

thanks for any suggestions.

 

[alldodge]

Am I reading this correctly?
The negative lead connection does not change

If I hook up a digital volt meter positive terminal to the ignition terminal on the switch and the other to the return terminal (ground) on the fuse box I get the same thing.

Pos lead is on the Purple wire (read 10-11V)

However, when I hook up the volt meter pos terminal to the batt terminal on the ig switch, I get battery volts.

Pos lead on Red/Purple wire (read 14.3-14.4V)

 

[Scott Danforth]

Ignition switch may be corroded internally

 

[Lou C]

Am I reading this correctly?
The negative lead connection does not change



Pos lead is on the Purple wire (read 10-11V)



Pos lead on Red/Purple wire (read 14.3-14.4V)

On both checks yes the negative terminal from the volt meter is connected to the ground point (return path) at the fuse box. I get battery volts at the B terminal on the ig switch and only 10 volts at the ig terminal on the ig switch with it switched on. For some odd reason F/W did not use standard colors for the battery lead at the ig switch, it is orange, the ignition lead is purple, start is yellow/red.

 

[Lou C]

Ignition switch may be corroded internally

I wish it was that, I replaced the old switch with a Cole/Hersee, same result.

 

[Lou C]

What I am thinking of doing next is disconnecting the ground (return path) lead for the gauges at the gauges and connect the digital voltmeter between this lead and battery voltage to see where I am losing voltage. Make sense?

 

[alldodge]

The ignition switch has one main pole which connects to power and start. To get a higher voltage on one side and lower on the other, even though the switch has been changed, it has to be the switch. This could be proved out by jump across the bat and ignition tabs and see if power is the same.

What I am thinking of doing next is disconnecting the ground (return path) lead for the gauges at the gauges and connect the digital voltmeter between this lead and battery voltage to see where I am losing voltage. Make sense?

Would agree if there was the same voltage at the other side of the switch

 

[tpenfield]

I would look for heat in the wiring. Turn on lots of electronics, etc to draw more current and see if you can use an IR Temp gun or even just by touch to see if you can find a 'hot' wire or connection.

 

[Lou C]

Thanks all for the suggestions, I am going back at it when it quits raining later today. I realized when I checked the voltage at the ignition tab on the ignition switch, I still had the ignition lead hooked up which obscured the results. I should have disconnected it and connected the voltmeter between the ignition tab and the ground on the fuse box, with the switch turned on. I will do that later, and see if I get the same 12.6v battery volts I get at the battery tab. Then I am going to disconnect the ground for the voltmeter and hook up a jumper wire between the ground terminal on the gauge and the ground at the fuse box. If this gives the same low volts, then I know its in the positive feed to the gauge. If on the other hand, this gives me close to battery voltage, then I know its in the grounding for the gauges.

This boat still has the original Medallion gauges which used a push on style of connector that goes onto a threaded stud. I bet these all have oxidization/corrosion in the terminals, although the only one that is reading off is the voltmeter, the gas gauge, temp gauge and oil pressure are all reading normally and the gauge lighting works.

 

[alldodge]

Most gauges will work correctly so long as voltage is around 7 to 18 vdc

 

[Lou C]

I would not be surprised if that whole grounding system for the gauges is the issue. I might just disconnect it and make up a new one and run it to the ground tab on the fuse box. The boat has been moored in salt water for approx. 16-17 seasons, been in the salt air a lot.

 

[Lou C]

I spend about 2 hrs under the dash today. I checked all the connections for the gauges, and grounds and surprisingly did not find corrosion. I was able to unplug the connecters in the harness (the harness, fuse box and gauges were all made by Medallion) and didn't find corrosion there either, everything was surprisingly clean. Ignition switch checked out OK as well. When I ran a jumper in place of the ground wire for the voltmeter, I got the same 10-11 volts, suggesting that the problem is not in the grounding system. Next I disconnected the positive lead to the voltmeter and ran a jumper wire from the ignition terminal on the switch. This gave me battery voltage (12.6) which suggests that the problem is in the positive feed to the dash wiring. The issue is that I don't have a good wiring diagram for this Medallion system and its difficult to figure out how the current is supposed to flow. Any other thoughts would be appreciated....​

 

[alldodge]

Measuring voltage drop with the meter consist of place Neg probe on one end of wire and Pos probe on the other. Anything much above 0.1V is to much

 

[Lou C]

Did some more checking, I had a long 10 gauge wire with aliigator clips on either end. As a test I hooked up one end to the fuse box negative terminal and the battery neg post. No difference in volts in on the voltmeter, still about 10.5-11V. Then took the same wire and hooked up to the fuse box positive and the positive post on the battery. The voltmeter jumped up to battery voltage and with the engine running, the voltmeter read the same as my digital voltmeter on the battery (14.3V). And all the accessories in the dash wiring worked as they should, blower, radios etc. As a test I put a fuse on one end with a ring terminal, hooked that up to the battery switch common post and the connected the other end to the fuse box positive. Did voltage checks with the ignition off, on and engine running. All were as they should be so the resistance was in the positive feed to the dash wiring. I was doing some reading on the Seaswirl owners website because a lot of their older boats were OMC rigged, probably with the same wiring harness as mine. And a few owners had the exact same problem, a lack of current capacity to the fuse box and did the same thing, adding a positive wire to help carry the load on the system. While it is not the orthodox way of fixing a problem like this, it may be better than trying to pull apart a 30 year old harness.

 

[alldodge]

If adding an additional wire to feed power fixes issue, then the original wire has the issue