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Strange electrical behavior - need advice 1996 5.7 L

I just read through this and see some great advice being offered by KGHOST! I'd suggest following it!

I have a question for KGHOST re; the engine/hull harness connector.... I think you're calling it a 10 pin!
Do these still use the round split pins? The ones that can become a bit collapsed and loose some continuity?

If so, can they be spread open some to gain continuity?
I've done this in years past with the older Mercruiser harness connections.
Is there any chance that something like this could be part of the issue at/on one or more of these circuits?

.
 
RicardoMarine said:
I just read through this and see some great advice being offered by KGHOST! I'd suggest following it!

I have a question for KGHOST re; the engine/hull harness connector.... I think you're calling it a 10 pin!
Do these still use the round split pins? The ones that can become a bit collapsed and loose some continuity?

If so, can they be spread open some to gain continuity?
I've done this in years past with the older Mercruiser harness connections.
Is there any chance that something like this could be part of the issue at/on one or more of these circuits?

.
Click to expand...


I believe that the connectors are the round pin split type you refere to. I did not think of this.......Many other issues going on here at home so my memory is a bit diverted. Good call!!

Some good dielctric grease also after the pins are confimed to be OK would be good. Also do not spread them too much they can break!!
 
kghost said:
I believe that the connectors are the round pin split type you refere to. I did not think of this....... Many other issues going on here at home so my memory is a bit diverted. Good call!!

Some good dielctric grease also after the pins are confimed to be OK would be good. Also do not spread them too much they can break!!
Click to expand...
Ditto!
Good call back at ya! :D

BTW, the older AQ series Volvo Penta engine/hull harness connections weren't any better, if at all.
We have issues with these as well..... especially the helm POS/NEG and start solenoid circuits. :mad:
One good and additional reason to run a new/fresh dedicated circuit foward for Nav equipment, etc.
But that's a different story...... for another day!

.
 
kghost said:
...Hook up your remote starter rig to the motor, do your voltage check at the connector pin. One meter lead to the pin, one to ground. Does your voltage equal the test of your alt, orange wire??? If so we can say the engine wire harness is good. If not the we have an issue with the motor wire harness/connection within the harness. If it is good then go to next step....
Click to expand...

Thanks KG, I'm hoping to be able to implement your plan after work tonight. One question on the above, though. When I was testing the ALT yesterday, I noted that the orange wire voltage would be roughly 0.5-0.7V higher than the purple wire on the ALT. Readings I would get with the harness disconnected would be Orange: 15V, Purple: 14.4. So based on that, am I looking for the PIN 6 output to match the purple wire reading, the orange wire reading (both from the ALT), or the Battery+? (I recall that the Battery+ was typically in between the purple and orange wire voltage readings).
 
At this point dont get stuck on a specific voltage.... The key here is it is above 13 or as you said 14 ish and does not drop down as seen on the dash guage.

Keep it simple and try not to get to caught up on +/- a half of a volt or so. Not at this point...
 
KG, thanks for all your continuing advice and step by step instructions. Here are the (as of yet unsuccessful) results of tonight's testing:

I confirmed that the engine side of the main bus is good, with no drop in voltage between the output of pin 6 and the ALT orange output. So, I got to testing the front end. Remember the symptom that I'm looking to see change is the drop in voltage when I rev the motor. (I noticed tonight that the voltage will stay around 12V when starting, but will j8ump to 14-15V once I rev the motor once, and then will stay there. But if I rev the mnotor again, the dash gauge and multimeter show a drop of ~.7-1.5V. Just want to make sure that is not normal, so that I'm not chasing a phantom problem.)

1. Removed the key switch again, and confirmed that the voltage on the power lead was roughly the same as at the ALT output of the same color. With motor running using rmeote rig, same result.
2. Added a 10gauge wire direct from Battery- to the ground bus up front (to try to rule out a faulty ground somwhere along the run) - no change in the problem symptom.
3. Started chasing the purple wire, by disconnecting at tach and other gauges, and trying to find the one that leads back to the engine. My Clymer manual has a full wiring diagram of the engine wiring, but doesn't seem to have a diagram from the dash. And, the wiring is all bundled and I'm having a bit of trouble tracing the underdash wires. But the strange thing is that I found +12V on some of them, and open circuit on others. That got me to thinking that I first need to understand what the purple wire does. I know that on the ALT when runing, I see a +12V (or more, usually a full 1V below Orange). So I was up front looking for a hot lead. But, when I remove the key switch from the circuit, all the purple lines are dead. So as I think about it, does the circuit work like this: key switch to "on" connects the purple lead to +12V, powering all the gauges and sending (what I assume is) a +12V to the field circuit of the ALT? If that is correct, then I assume that the purple wire "originates" at the key switch, runs to all gauges, then runs to the run/off switch in the throttle, and then back to the motor. That would explain why one can turn the run switch off and kill the motor without turning the key off or shutting down the gauges. That should get me through your test, to determine whether the gauges are the issue. Then I can start disconnecting them in series...

Assuming I have that right, the plan tomorrow will be to do a continuity test between the purple lead on the ALT to the purple leads at the switch. I'll see if I can find the lead that will send power to the motor but not the gauges. I will probably also have to unbundle the whole mess in order to visually trace.
 
Yes you are correct. The purple wire ORIGINATES at the key switch and does power the guage cluster when the key is on.

One more note: If some of your guages lite up when the key is in the on position and are not controlled by a seperate switch then this may create a voltage drop.

Here is the Merc schematic of a typical dash wiring set up


View attachment 2161
 
Well, tonight showed success...and failure. I managed to trace the wire based on KG's post, and confirmed that I get no voltage drop with increased revs when the only things in circuit are the key switch, run/off switch and the purple wiring from run switch to the ALT. Then I started adding in components, each time checking the ALT output (orange) for total and changes in voltage. Tachometer (which I was SURE was the culprit, came out clean. Next, connecting the voltage meter into the purple circuit did not create the symptom. Next, the warning buzzer (which feeds off the voltage meter) - still no issue. BUT... as I was finishing the last test, I noticed that the dash voltmeter WAS showing a drop in voltage, even though the ALT output had remained steady at 14-15V (or rose slightly) with increased revs. So I went back and did the same process (nothing in circuit, then adding tach, and then voltmeter, but htis time using the multimeter on the purple output at the ALT. What I found is that the purple lead from the ALT did not seem to react at all with nothing in circuit (meaning, it did not seem to drop or rise by more than 0.3V). It seemed to react a bit when I added the tach, but not conclusively (the swings were still ~0.4V, and with a digital it is tougher to see the "trend" downwards unlike the analog gauge). Adding in the analog voltmeter and buzzer, and I did see a drop in voltage with increasing revs - not much, roughly 0.5V, and the analog voltage gauge in the dash also showed that behavior. At that point, I figured I would stop and see what folks had to say. Based on this, I can't now tell whether I'm chasing a ghost. It appears that unlike before, the Orange output is charging all the time, going up with increasing revs. The Purple output exhibits the reduction in voltage when the tach and voltmeter are in the circuit, but I can't tell whether that is "normal" to have the dash power lead drop in voltage while battery and ALT output do not. So, my next plan is to use a second multimeter on the dash purple voltage, and/or a new analog gauge. If the voltage drops on those with just the tach in circuit, I think I'm looking at a tach that is draining excessive voltage as it tries to display changes in the motor speed. Or, that's how it is supposed to work and I'm now wasting my time... :) I may also run a separate switched circuit off of either the organe lead or the battery lead up to the dash, and install a second voltmeter in the dash so as to keep an eye on whether the system is truly charging when underway.



Thoughts?
 
If you could when you post voltage info, instead of what you see as a change (.4, .7) post it as the actual votlage (13.6. 14.2 etc etc.) Hate doing math!!!

At this point I would GUESS that you may be looking at a weak connection. I understand how frustrating this is as I have had very similar issues before so dont get discouraged!!

There should be a 20 amp fuse or breaker that I belive is inline with this power to key circut. Have you looked at this closely? Typically is is labeled IGNITION.

Pull this fuse and/or inspect the connections here. If this is weak what it will do is cause a severe voltage drop on a guage with no affect on the actual operation of the charging circut...

WHat is happening here in my opinion is when all guages are connected this is creating voltage drop and may be due to a bad wire connector (ring terminal or what ever you have on your wire ends)

The reality is your volt meter will normally read at 2000 rpms ~ 13.5 -14.5 volts. So anything below 13.5 is an issue (unless lights and accessories are on) then it iwll read lower than normal.

Closely look at each guage and the ground wire that is going to it. Remeber that the ground wire(s) are the other half of the circut. If one of those are not good then this can create this issue. SO make sure all grounds are good......

Just for additional info. I have a 1987 boat, this boat suffered some extra moisture for a season when I had a new cover made for it and it did not vent propperly and held moisture inside. (wrong material used by cover maker!!!!). My guage cluster in my dash took a beating due to this moisture......Almost all my connections (which are spade not ring) connected to all my breakers are oxidized. This creates all kinds of electrical gremlins.....Because I understand this and I tend to be a bit lazy on rewiring my whole dash I see it as, it is what it is.lol
 
KG, good point on specifying the voltage. I've run the tests again tonight, this time with an analog multimeter on the dash and the digital monitoring the purple lead on the ALT. The voltage on the purple lead of the ALT would be at 12.0-12.4V when the motor is first started, and then jumps to 13.5-14.3V once the motor is revved once (is that normal?). Once the ALT starts charging, I saw voltages on the ALT purple lead remain in the 13.2-13.6 range, with the lower numbers being seen when the motor revved (inverse relation of the revs and voltage at the ALT purple lead). The analog mulimeter registered no change between the key switch purple lead and a good ground (which makes sense since the only element between that lead and battery power is the switch). So I added an automotive voltage meter on the last purple lead in the series (my purple wiring originanates at key, goes to half the guages in series and then to the tach, where it splits with one lead going to voltmeter and oil pressure and the other going to the kill switch and to the ALT). I saw the same drop in voltage at the "other end" of the circuit (meaning, I compared the behavior at the key switch and then with all the gauges in between the switch and my test lead). Voltage readings were in the 13.2-13.7 range in the dash, 13.0-13.5 at the ALT (with a strange momentary ddrop to 12.5V at one point).

I did clean the contacts on the circuit breaker, and a continuity test showed about 1 ohm. I probably should shunt across that circuit breaker for testing and see if the behavior is the same. I also ran leads from the various grounds to a good ground, to try to offset any bad connections - no effect.

So, given that I'm now seeing purple input and orange output in the 13V to 15V range consistently, I'm wondering if the drop in voltage on purple is actually correct. Is the purple wire the power lead for the ALT field? Would it be natural for the field voltage to drop as the stator speed increases (generating current?). I don't know, but apart from a ~0.5V fluctuation (13.0-13.5) when the motor revs, I see not other indications of an electrical problem. Maybe it is time for a checkout run?
 
At the Alternator:

Orange. = output

Purple. = excitation

Red/purple. = sensing

Black. = ground

The voltage on the purple lead of the ALT would be at 12.0-12.4V, Yes this should be the same on any purple connection with engine not running

when the motor is first started, and then jumps to 13.5-14.3V once the motor is revved once (is that normal?). Yes the alt will not output until excited.

I am no expert with altenators..........kinda voodoo for me. I kinda understand them but do not quote me on all of there function....lol



I still think we are dealing with a bad connection or weak something some where.

There are a couple of other areas to look at.

first.
I just reread the whole post, Do yourself a favor, disconnect one battery for the circut, temporarly remove the battery switch from the circut. Wire one (known good 12.6 static voltage) battery directly to the starter as if the boat came with only one battery and no battery switch. Re start and monitor the volt meter. Report what happens back to us.... Make sure the ONE battery is fully charged!!

My thought here is having two batteries and one not so good could and would cause a voltage drop.

Also try doing this test, just for the sake of one more thing, disconnect the purple wire going to the choke after the engine is warmed up. see if this has any impact on the readings........you "may" have to remove the flame arrestor and stick a screwdrive handle in the carb to keep the choke fully open.

You may be dealing with a battery issue or battery switch issue.........


Here are some other tid bits but may not be an issue at this time but keep in the back of your mind incase nothing else seems to work.


Also in the engine wire harness there is a terminal point where the purple wires meet. this is or may be a bunch of ring terminals connected with a small screw and taped up real good. This maybe an issue. weak connections.

Also the red with purple wire is also at many points on the engine, the slave solenid, the large breaker with the red button. Look at those carefully and see if there is a connection issue.

Just for your info
 
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Well, at long last, I think I can report success. After having my neighbor come over to politely ask how much longer I would be working on the boat and revving the motor (in fairness, it was 9:30pm for the third night in a row), I decided to take it out on a small local lake and test out the theory that something in the purple ignition lead or ground wires of the dash was faulty. After three hours on the water (and a nice sun burn) I determined to fully replace all of the purple wires in the dash. I finished that today, and tested it (on land). The system charged correctly on the orange wire (15V), and registered 14+V on the purple wires. Voltage drop was negligible when revving - 0.1V or at most 0.2V (14.1 down to 13.9-ish). So I don't know what it was, but I know the scattershot approach worked. Oh, and the rough runnig from earlier - determined that was just old gas (thanks California for the 10% ethanol). Many thanks to all who helped, and in particular to KGHost. KG was so instrumental, patient and reliable (for several days, he responded each night to my latest posts). Thanks again!
 
You mentioned earlier that the alternator belt was tight - good. But remember that the alternator's resistance to rotate goes up as rpm and output demand increases. Often this directly leads to slippage at the belt, and old highly polished belts are more likely to slip under load even when "tight". Consider installing a new belt to see if that reduces slippage and voltage drop at higher speeds. If it doesn't, at least you then have a spare belt. Belts will slip a lot before they get to the point of squealing.
 
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