3.0L Mercruiser TKS turn key start no ground

[spcali]

Hello,
I got a 2006 3.0L with a TKS carburetor that has no “ground” at black/yellow wire #18 with “key off.” This is the connector heading to the enrichment solenoid that connected directly to the carburetor(TKS system).
Steps Taken:
1. I took a volt meter to pin 18 -A purple/ red wire to battery ground. Got 12v
2. Replaced Oil pressure switch that connects to terminal 9
3. Checked continuity for a broken wire at blk/yellow wire 18-A to 9-A blk/yellow wire, Is good it rings out.
4. Checked continuity at 18-A blk/yellow to 7-a blk/yellow wire, is good rings out.
5. Only thing left to replace, is a TKS temp switch on order p/n 87-866115 on order( Arriving Wednesday, Thursday)
I’m kind of stumped that I can have no broken wires heading to the oil pressure switch(9) enrichment solenoid for TKS (18) and TKS temp switch (7) but not have ground. Did I overlook something or then the TKS temp switch being bad?
Assuming I overlooked something, If TKS temp switch doesn’t give me ground at connection 18A, would it be safe to just run a wire from 7A to 18A it appears it would be the same wire or be the same.
Any suggestions are appreciated, I plan on rechecking again today in case I missed something…..I also checked at the connection pins(see yellow arrow) I added a few photos for reference , including circuit diagram.

 

[spcali]

Hello I posted this in Electical boat restoration, but thought Mercruiser area is more appropriate.


I got a 2006 3.0L with a TKS carburetor that has no “ground” at black/yellow wire #18 with “key off.” This connection should have power with key off from what iThis is the connector heading to the enrichment solenoid that connected directly to the carburetor(TKS system).
Steps Taken:
1. I took a volt meter to pin 18 -A purple/ red wire to battery ground. Got 12v
2. Replaced Oil pressure switch that connects to terminal 9
3. Checked continuity for a broken wire at blk/yellow wire 18-A to 9-A blk/yellow wire, Is good it rings out.
4. Checked continuity at 18-A blk/yellow to 7-a blk/yellow wire, is good rings out.
5. Only thing left to replace, is a TKS temp switch on order p/n 87-866115 on order( Arriving Wednesday, Thursday)
I’m kind of stumped that I can have no broken wires heading to the oil pressure switch(9) enrichment solenoid for TKS (18) and TKS temp switch (7) but not have ground. Did I overlook something or then the TKS temp switch being bad?
Assuming I overlooked something, If TKS temp switch doesn’t give me ground at connection 18A, would it be safe to just run a wire from 7A to 18A it appears it would be the same wire or be the same.
Any suggestions are appreciated, I plan on rechecking again today in case I missed something…..I also checked at the connection pins(see yellow arrow) I added a few photos for reference , including circuit diagram and carburetor manual (41)
https://www.scribd.com/doc/88364069/Service-Manual-41

 

[alldodge]

On the 3.0 the TKS Blk/Yel is grounded by 2 things
Temp switch makes connection after motor warms up
Oil Pressure is present (motor running)

Block diagram

 

[sam am I]

no “ground” at black/yellow wire #18 with “key off.”

It's an "active" ground it appears........Meaning something (a switch/sensor) completes the ground when active.

e.g., a one wire oil pressure sender after the engine starts AND it reaches pressure(say 5 psi), closes a internal switch that completes a ground connection through the body of the sender to the engine block(ground). Hence, "active ground"

So no, with key off, the blk/yel will read "open" to ground. HOWEVER the pure black is always grounded, key on or off.

 

[spcali]

Thank you! So if I understand correctly, with key off not running this connection won’t be grounded? Don’t know too much about electrical system…

 

[spcali]

It's an "active" ground it appears........Meaning something (a switch/sensor) completes the ground when active.

e.g., a one wire oil pressure sender after the engine starts AND it reaches pressure(say 5 psi), closes a internal switch that completes a ground connection through the body of the sender to the engine block(ground). Hence, "active ground"

So no, with key off, the blk/yel will read "open" to ground. HOWEVER the pure black is always grounded, key on or off.

I also read this:

On 3.0L engine the oil pressure switch provides ground path for TKS module . Positive voltage is supplied continuously through a 20amp directly from engine circuit.

So ground is only created when the engine is pressurized to 5psi, or we’ll say running. Not with key off? Engine off?
Just trying to understand as best I can, as the verbiage on the Mercruiser manual sounds confusing(see “operation”)

 

[alldodge]

Correct
and as shown in post 3, ground is also applied once the motor waters up and the Temp switch makes connection. Then so long as the motor stays warm it will keep the ground even with key OFF

 

[spcali]

Correct
and as shown in post 3, ground is also applied once the motor waters up and the Temp switch makes connection. Then so long as the motor stays warm it will keep the ground even with key OFF

Thank you!