Weird Ignition System Issue

[Dan_A]

I've got an issue that really has me scratching my head. I'll explain it the best I can.

I'm in the process of restoring a 1998 Falcon Thunderbird (5.7L Merc), I have the engine ready to fire up but first had to replace the starter. The old one made a clicking sound and failed my bench test. So I purchased a new starter. Yesterday I put the starter on, turned the key, and nothing. Not a click, hum, or anything.

-From here I checked that battery power was okay.
-Checked power to the starter and the was power from the main terminals, but no power to the ignition wire when key was fully turned.
-Checked that the ignition switch was okay.
-Checked continuity from the ignition to the starter.


-Checked power to the ignition and noticed something odd. When connecting negative end of my multimeter to the battery ground terminal and the other to the ignition switch power cable I read 0 volts.

out of curiosity I connected positive end of the multimeter to the battery positive and the negative end to the ignition switch power line, it showed positive 12.5v.

my understanding is that the starter pulls ground from where it connects to block and we send 12.5 volts straight to it from the batter and a lower amperage 12.5 volts from the ignition switch to activate the solenoid/ relay and draw the current directly from your battery to start the engine.

so my thought is that somehow the polarity of the ignition switch has switched? It's now sending the negative side of the circuit therefore never closing the circuit and explaining why I read no power there.

I wired the new exactly the same as the old one shown in the picture. Close large terminal is ground, Far large terminal had the orange and both red wires, small terminal closest the block had the ignition switch, other small terminal wasnt used. All accessories come on.

any suggestions or advice are welcomed!

 

[Dan_A]

I should add that I checked for continuity on the circuit breaker behind the air cleaner. Looked rather corroded but checked out with continuity

 

[dingbat]

I've got an issue that really has me scratching my head. I'll explain it the best I can.

I'm in the process of restoring a 1998 Falcon Thunderbird (5.7L Merc), I have the engine ready to fire up but first had to replace the starter. The old one made a clicking sound and failed my bench test. So I purchased a new starter. Yesterday I put the starter on, turned the key, and nothing. Not a click, hum, or anything.

-From here I checked that battery power was okay.
-Checked power to the starter and the was power from the main terminals, but no power to the ignition wire when key was fully turned.
-Checked that the ignition switch was okay.
-Checked continuity from the ignition to the starter.


-Checked power to the ignition and noticed something odd. When connecting negative end of my multimeter to the battery ground terminal and the other to the ignition switch power cable I read 0 volts.

out of curiosity I connected positive end of the multimeter to the battery positive and the negative end to the ignition switch power line, it showed positive 12.5v.

my understanding is that the starter pulls ground from where it connects to block and we send 12.5 volts straight to it from the batter and a lower amperage 12.5 volts from the ignition switch to activate the solenoid/ relay and draw the current directly from your battery to start the engine.

so my thought is that somehow the polarity of the ignition switch has switched? It's now sending the negative side of the circuit therefore never closing the circuit and explaining why I read no power there.

I wired the new exactly the same as the old one shown in the picture. Close large terminal is ground, Far large terminal had the orange and both red wires, small terminal closest the block had the ignition switch, other small terminal wasnt used. All accessories come on.

any suggestions or advice are welcomed!

https://forums.iboats.com/forum/eng...ves/603989-1997-mercruiser-5-7-starter-wiring

 

[Dan_A]

That seems to be a different issue, my starter is wired properly as confirmed by a bench test where the starter does its job. When in the boat it doesnt seem to be getting positive power from the ignition, but instead its sending ground through

 

[alldodge]

Close large terminal is ground, Far large terminal had the orange and both red wires, small terminal closest the block had the ignition switch, other small terminal wasnt used.

Which close terminal is ground?

And where does the wire go the arrow is pointing?

Assume wires are on there just for the pic and not the actual connection

 

[Dan_A]

Which close terminal is ground?

And where does the wire go the arrow is pointing?

Assume wires are on there just for the pic and not the actual connection

I'll have to confirm but the wire for arrow points to goes to the circuit breaker. This breaker seems to be okay since there is continuity there. Ground is the large post nearest the starter motor.

I get power to the starter through the large leads but not from ignition when the key is turned. So nothing is telling the starter to kick on. Im beginning to wonder about the slave solenoid, i'm 95% certain the ignition switch is good.

 

[alldodge]

Ground is the housing of the starter it self. The starter has no wires that are shown or can be seend which go to ground.



Suggest, use the voltmeter function trace power. Use a connection to the Negative battery post or engine block

On starter top post 12V
Should be 12V on both post of the 50 amp breaker
Should be 12V on slave relay on motor Red/Purple wire
Should be 12V on the Red/Purple wire at the key switch

When key is turned to ON, should be 12V on Purple wire of key switch
When key is turned to start, should have 12V on Yellow/Red wire

With Key ON, should be 12V on + side of coil
With key is start position, should be 12V on small Yellow/Red wire on bottom of slave relay

Slave relay should energize with key in start position and transfer main power from Red/Purple large wire to Yellow/Red large wire to starter solenoid

 

[Dan_A]

When checking power at the ignition switch I came across this. Does this count as power going to the ignition switch?


"Checked power to the ignition and noticed something odd. When connecting negative end of my multimeter to the battery ground terminal and the other to the ignition switch power cable I read 0 volts.

out of curiosity I connected positive end of the multimeter to the battery positive and the negative end to the ignition switch power line, it showed positive 12.5v. "

 

[alldodge]

Which "switch power line" as in what color was the wire?

 

[Dan_A]

It's red.

And the starter needs a positive line on the red/yellow line that the switch has as an output. But it looks to be reading as a ground

 

[alldodge]

I'm just not following what your saying. Standard color wires is the major color and then the stripe (Yellow wire with a red stripe is Yellow/Red). Your motor should not have a Red/Yellow so its probably just method of understanding and that's all good.

The 1998 5.7 used a electric fuel pump so there should also be a Purple/Yellow wire that goes on the other small post on the starter. This wire goes to an oil pressure switch which then powers the fuel pump once the motor starts.

Here is the helm to motor wiring



Here is some of your motor wiring

 

[Dan_A]

My apologies I didnt know the convention for wire coloring. It is in fact yellow/red then. However this is carborated and I have not seen the purple/yellow wire. Not on the old starter either which used to run. It's the 5.7 L MCM

I just tried jumping the slave solenoid and got a clunk but nothing more

 

[alldodge]

I just tried jumping the slave solenoid and got a clunk but nothing more

If the starter engaged and you got a clunk, then the motor may be seized. Suggest pulling all the plugs and see if you can turn it over by hand. If hand doesn't work then try again with the starter

 

[Dan_A]

Plugs are out, I can turn it by hand! That's why i'm very confused, starter works too im sure of it.

 

[alldodge]

If the clunk was the starter then that is weird. If the clunk was the relay then maybe thats the issue

 

[dingbat]

When in the boat it doesnt seem to be getting positive power from the ignition, but instead its sending ground through

Your assuming the slave is powered from the key.

Typically the power from key is only used to power the ignition. The slave is powered through the starter. The key is simply a remote, normally open contact closure, to control the slave relay

 

[Dan_A]

I have a new solenoid, i'll throw it on today

 

[Dan_A]

Starter will spin the engine with the sew slave solenoid when the large posts are jumped. Ignotion issue still hasn't been found.

it was enough that I was able to run a compression test and my results are confusing. This boat was running before its starter went out. But I got some very very low compression readings on 2 cylinders and 2 rather low. I'll try to type it out instead of attempting to post a picture.

Prop
1 - 73 5 - 30
2 - 73 6 - 40
3 - 100 7 - 95
4 - 100 8 - 100

 

[Dan_A]

Starter will spin the engine with the sew slave solenoid when the large posts are jumped. Ignotion issue still hasn't been found.

it was enough that I was able to run a compression test and my results are confusing. This boat was running before its starter went out. But I got some very very low compression readings on 2 cylinders and 2 rather low. I'll try to type it out instead of attempting to post a picture.

Prop
1 - 73 5 - 30
2 - 73 6 - 40
3 - 100 7 - 95
4 - 100 8 - 100

 

[Dan_A]

Your assuming the slave is powered from the key.

Typically the power from key is only used to power the ignition. The slave is powered through the starter. The key is simply a remote, normally open contact closure, to control the slave relay

So maybe it would be worth throwing in a new ignition switch?