Electrical Question (Merc 90)

[CharlieZulu]

Ever since I've owned this motor, this has bugged me..... there are two wires which someone has cut. They start at a terminal block on the right side of tthe motor and there are a number of other wires coming off the same point.

Also, my overheat and oil level alarms have never worked. Could these be connected?

This terminal block seems to be a common point for a lot of stuff. The two wires I am referring to go down to the right. One blue and one light brown.

Also..there's a red wire which doesn't go anywhere, but it hasn't been cut, it just terminates in a black female connector.

So what do there wires do?

 

[Silvertip]

Re: Electrical Question (Merc 90)

The tan wire looks like the temperature alarm wire. The overheat switch on the cylinder head has a tan wire on it. The previous owner apparently had a constant alarm (or worse -- a overheat issue) and cut the wire as a solution to mask a serious issue. Either the alarm is bad or the temp switch is suspect. Disconnect the bullet connector on the temp switch wire and measure resistance to ground. Should show open circuit on a cold engine. If it shows closed circuit on a cold engine the switch is bad.

 

[electricjohn]

Re: Electrical Question (Merc 90)

The red wire might be the +12 volts for the power trim relays. Do you have trim?

 

[CharlieZulu]

Re: Electrical Question (Merc 90)

Yep, I have trim. Here are some more clues...see my schematic sketch:

In my original pic you can see the blue and tan wire come together into a black tube and they disappear behind my oil reservoir. It's the cable with the lettering on it.

Here is where the black wire goes into the engine block. Overheat sensor?

 

[CharlieZulu]

Re: Electrical Question (Merc 90)

So, I didn't hear back from anyone......if you look at my sketch, it seems to me that yes, I have two cut wires, but from the same terminal other wires do seem to be going to the right places?? The tan and blue go into a black sheath, and also the tan does up into the engine body. (This is overtemp, right??)

I put labels on the pic:

 

[electricjohn]

Re: Electrical Question (Merc 90)

The two cut wires may go to the low oil alarm float in the oil tank. The float brings in an alarm when there is less than 1 qt of oil left in the tank. This float loses buoyancy as it ages and triggers false alarms, which is why the wire may have been cut.

 

[CharlieZulu]

Re: Electrical Question (Merc 90)

The two cut wires may go to the low oil alarm float in the oil tank. The float brings in an alarm when there is less than 1 qt of oil left in the tank. This float loses buoyancy as it ages and triggers false alarms, which is why the wire may have been cut.

Then where do the two wires go that I have circled in the above pic? I cannot trace them but I assumed they go to the oil tank (??)

 

[electricjohn]

Re: Electrical Question (Merc 90)

I looked at a diagram in my 1988 90 HP Merc. service manual and the blue and tan wires you have circled go to the oil tank. The two cut wires may have gone to aa alarm test button. My engine does not have the test button shown in my service manual. Don't know why. The single tan wire should go to the alarm (buzzer) somewhere at the helm. If you have a Commander type remote control (throttle), the alarm is in there.

 

[CharlieZulu]

Re: Electrical Question (Merc 90)

Just checked my oil tank, and I do not have the level sensor -- my tank does not have it installed.

curiouser and curiouser.....

 

[79camaro]

Re: Electrical Question (Merc 90)

Not sure about this post but note that some after market replacement parts don't use all the wires. I learned this from replacing the switchbox with a cdi switchbox. I thought it was odd that it had me cut a wire and tape it off, but it worked.