Low Voltage to the Ignition Switch

[Danno1966]

Hey all, I've been chasing a problem and have it isolated. Maybe you can fet me over the hump.
98 350 Mag Mpi B3 set up.
new batteries fully charged, new battery cables, starter, starter solenoid, alternator bla bla bla.
I have 11.6/11.7V at the ignition switch, and thus to the solenoid, circuit breaker, alternator and starter...low voltage while starting isn't fun. The Volt meter barely reads anything on the dash till the engine starts, then it, and a tester at the battery will read only 12.6/12.7V.
All other 12V connections read perfect. If I jump a wire from 12v source to the ignition switch all problems disappear. Batteries reading over 13 to 14V when running, the dash volt meter reads 12v with the key on...

So, what feeds the ignition switch, and why would just this have a low voltage issue Just in the starting circuit? Suggestions?

Dan

 

[kenny nunez]

Try unplugging the main cannon plug, then carefully spread each male pin, sometimes that is all that is the problem.
Also try to inspect the main harness from front to rear, I once encountered a drill hole in the harness from when the rub rail was installed. Be sure that every wire terminal behind the gauges are tight.

 

[Danno1966]

Try unplugging the main cannon plug, then carefully spread each male pin, sometimes that is all that is the problem.
Also try to inspect the main harness from front to rear, I once encountered a drill hole in the harness from when the rub rail was installed. Be sure that every wire terminal behind the gauges are tight.

I'll try that.
Does it make a difference that feeding good 12v to the ignition switch completely fixes it?

 

[Scott Danforth]

in addition to the cannon plug, clean all connections from the battery to the engine block and starter, from the starter up to the main breaker, then to the cannon plug. you have bad connection(s) somewhere

 

[Danno1966]

Is it hurting anything to use a jumper wire temporarily? I wouldn't think so, but...

 

[Scott Danforth]

Why not fix it correctly

 

[Danno1966]

Is the ignition switch fed from the battery through the plug, and then ba

Why not fix it correctly

I will. Like it said, temporary...

 

[kenny nunez]

The wire to the ignition switch comes from the harness. Can you tell if the harness is a genuine Mercruiser part. Some boat builders use a cheaper version. Bayliner is a good example. I just helped someone with a non mercruiser harness. We had to run new oil, temperature and ignition feed wires. This was on a 75 Glastron.

 

[Danno1966]

The wire to the ignition switch comes from the harness. Can you tell if the harness is a genuine Mercruiser part. Some boat builders use a cheaper version. Bayliner is a good example. I just helped someone with a non mercruiser harness. We had to run new oil, temperature and ignition feed wires. This was on a 75 Glastron.

I fully intend to pull the harness plug apart, but in the mean time, will it hurt anything to jump a wire from clean 12V to the ignition switch for a temporary solution?
I can easiky get a clean 12V to the ignition switch. Does it matter where it comes from?
All circuit breakers, and the neutral safety switch are all still in operation.

 

[kenny nunez]

Should not hurt, I forgot to tell you that before. It will be a good idea to have a fuse in the temporary circuit.

 

[Fun Times]

Did you replace the black ground battery cable to the engine block too? when you put a new red cable to the engine starter?

Also try wiggling some wires and cables around with the key on.

You may have a bad/dirty connection at the engine starter white fuse not allowing full 12.6 volts to the circuit breaker and orange wire to the Alternator... Also just to be sure, check the purple (and surrounding) wire/s out the back of the alternator for an open cut wire situation.




An example of a bad fuse at the starter,

 

[Danno1966]

The more I think about this (which can be scary) the issue must be between the battery and the engine harness plug.
Here's why I think that. Need your thoughts on this...
Every point that is hot in the starting circuit, at the starter (yel/red), the circuit breaker, the hot side of the solenoid, the alternator, even the hot prong of the ignition switch, all read 11.7V. BUT, if if I jump a good 12V to the engine circuit breaker, all is good. So I backed up and jumped 12V to the ignition switch, all is good. So it seems to me everything going TO the engine is fine, it must be the voltage coming from the battery, through the engine harness plug, then to the ignition switch that's the problem.
Follow my logic? Does it make sense?
Then I question, with all the different circuits going through the engine harness plug, why is JUST THIS one effected?
And here's another clue: the longer it sits, the higher the voltage gets. When it's been cranking, it may drop to 11.3V then as I watch the test meter, it will slowly go back to 11.7 ish. Don't know if that tells anything. Bottom line, I need to mess with the big plug.
Thoughts?

 

[Scott Danforth]

see post #4. start at the battery, remove every connection and clean them with 150 grit until they are shiny enough your mother in law will eat off them. then tighten the connection, and seal with marine electrical sealant. then move on to the next connection and repeat.

if your battery cables are crusty and crunchy, replace them. clean the new cables.

 

[Danno1966]

see post #4. start at the battery, remove every connection and clean them with 150 grit until they are shiny enough your mother in law will eat off them. then tighten the connection, and seal with marine electrical sealant. then move on to the next connection and repeat.

if your battery cables are crusty and crunchy, replace them. clean the new cables.

What are the possibilities of a bad 90 amp fuse causing a low voltage condition? Seems like everything from that point has low voltage. The starter was replaced, but not the 90 amp fuse. Can it be tested for resistance?

 

[Scott Danforth]

doubt its the fuse itself. however most likely the connections.

 

[nola mike]

Fwiw I've had a bad fuse that tested fine statically that wasn't passing enough current under load. But still least likely.
Only a few connections to fail. Most likely are ignition switch, fuses, cannon plug, gauges, and dead man switch. Probably a combination though. If everything if perfect with a jumper to I terminal then downstream (gauges, dead man) is good. Jumper to B terminal rules out ignition switch. Measure voltage to ground on both sides of each connection. You might get lucky and find a big difference. Better test is a voltage drop test across Cannon plug and ignition fuse (<--my bet if it's a glass fuse). With ignition on measure the voltage across the connection (both probes connected to the purple wire. There should be minimal voltage reading. Anything greater than a couple of ⅒ v is a problem.

EDIT: Rereading this. Your ignition circuit shouldn't affect cranking speed. As long as you're getting enough juice to trip the slave solenoid, the starter is getting power from the battery, so problem is in that circuit as mentioned in some of the posts

 

[Danno1966]

Update!!!
The Cannon plug still had only 11.7 V on the pur/red wire.
Going to the 90 amp fuse on the starter...had 12.6 v to the battery (#1) but only 11.7 on the back side (#2).
Ordering a new fuse, and jumped a wire to the Ignition switch in the mean time.

 

[Lou C]

I had a no crank no gauges condition one year that was caused by oxidation on the glass fuse base and tabs in the fuse box, for the ignition system. Fuse had continuity but there was too much oxidation for current to pass.

 

[nola mike]

Did you clean those connections at the fuse? Still not seeing how a jumper to the ignition switch would fix a slow crank condition. Did you try jumping at the starter?

 

[Danno1966]

I havent attacked the fuse yet, only because t's really difficult to get to, and I'm not a young, or limber (or small) man anymore, but I'm going to replace it soon.
My thoughts on why it worked, remembering i am, let's say, an advanced novice on electrical. First, it worked to jump anywhere into the starting circuit. Since it was low voltage, not no voltage, adding a 12v source is like a booster. I basically bypassed the fuse from a different clean circuit, kinds like through the back door. I fed it from the main 12v block at the helm, which is straight from the battery. I dunno...but it works. It will only be temporary and the fuse will be replaced well before the busy boating season is back, but we do use our boat year round.