Slave solenoid installation

I have an AQ 255A, 5.7 liter M, which originally had a Prestolite starter, V/P 834893. I'm about to install an API 10082HI gear reduction starter. I was advised to install a slave solenoid to supplant the solenoid attached to the starter. How do I wire it? Is it enough to simply attach the yel/red lead from helm ignition switch to the appropriare post on the slave solenoid, then continue the lead from there to the proper post on the starter solenoid, leaving the 4ga cable from master battery switch and the three 10ga wires for cabin lights etc, attached just to the proper post on the starter solenoid? I would of course ground the remote slave solenoid.

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ocoocher said:

I have an AQ 255A, 5.7 liter M, which originally had a Prestolite starter, V/P 834893.
That would have been the old Bendix drive motor.

I'm about to install an API 10082HI gear reduction starter.
Make sure that:
.... this is correct for the flywheel..... (straight across bolt pattern for 153 tooth ring gear)
.... you get the correct bolts with the new motor.

I was advised to install a slave solenoid to supplant the solenoid attached to the starter.
Your new HTGR/PMGR starter motor uses a solenoid for both lever action pinion gear engagement, and electrical armature circuit contact.
Unless your stater motor "helm to engine bay" solenoid circuit is weak, a slave solenoid is not necessary.


How do I wire it? Is it enough to simply attach the yel/red lead from helm ignition switch to the appropriare post on the slave solenoid, then continue the lead from there to the proper post on the starter solenoid, leaving the 4ga cable from master battery switch and the three 10ga wires for cabin lights etc, attached just to the proper post on the starter solenoid?
Can we see a picture of this arrangement?

I would of course ground the remote slave solenoid.
Although the term is commonly used........ there is no "ground" in a 12 vdc system..... Positive and Negative only.

Click to expand...

I'll add to my previous post.

Your AQ series SBC will be using the flywheel with the 153 tooth ring gear.
This requires the straight across bolt pattern starter motor (not the staggered bolt pattern).


The old Bendix drive motor's solenoid served as an armature circuit contactor device only.
The pinion gear (via the Bendix spiral splines principle) was kicked out into the flywheel ring gear via quick armature torque.
(No lever action from a solenoid required)

Your HTGR/PMGR replacement motor's solenoid serves two purposes......
1..... kicks the pinion gear into the flywheel ring gear, and 2.... simultaneously makes armature circuit continuity.





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Thank you Rick. My post was incomplete. I replaced the original Prestolite starter with an API ST82 years ago. Last year I installed the replacement for that - It failed recently and is being replaced under warranty by the mfr, API of Ft Lauderdale. They have advised me to install a slave solenoid. I frankly do not see the need, but I will comply given the warranty replacement. I have returned the defective unit and await the replacement so no pic to send, but here is the link to the website page showing this starter - http://www.apimarine.com/mm5/merchant.mvc?Session_ID=f65529d7295cfc8047a883044734957b&Screen=SRCH
Since the slave solenoid won't be mounted to the starter or engine, I will run a "ground" or negative lead to the engine block.
My question is simply whether my positive lead from battery via master battery switch and the smaller positive leads for cabin lights etc need to attach first to the slave and then to the solenoid on the starter, or can bypass the slave? In the latter case, the only connection of the slave to the primary solenoid would be the yel/red 16ga wire from helm ignition switch. API said run the positive battery etc to the slave and then to the primary solenoid, if I understood correctly. But I don't see why and have my doubts.

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ocoocher said:

Thank you Rick.
You are welcome.

My post was incomplete. I replaced the original Prestolite starter with an API ST82 years ago. Last year I installed the replacement for that -

Chris Craft & Volvo Penta V8 12V 9-Tooth CW Rotation, Replaces Volvo#834893 - API 10082HI .

It failed recently and is being replaced under warranty by the mfr, API of Ft Lauderdale. They have advised me to install a slave solenoid.
If curious, ask them to explain why!


Since the slave solenoid won't be mounted to the starter or engine, I will run a negative lead to the engine block.
Yes.... as you can see in my schematic below, the Engine Block becomes the "system Negative common" point for all Negatives.

My question is simply whether my positive lead from battery via master battery switch and the smaller positive leads for cabin lights etc need to attach first to the slave and then to the solenoid on the starter, or can bypass the slave?
Look closely at my schematic.
** Keep in mind that the slave solenoid involves energizing the magnetic coil side of the main starter motor solenoid.... not the load side!

Unless there is an unusual requirement, all 12 vdc power will be derived from the Common Cable, but NOT necessarily from the starter solenoid post. This can also come from the MBSS "common" terminal.
(MBSS = main battery selector switch)


In the latter case, the only connection of the slave to the primary solenoid would be the yel/red 16ga wire from helm ignition switch. API said run the positive battery etc to the slave and then to the primary solenoid, if I understood correctly. But I don't see why and have my doubts.
Occasionally slave solenoids are used for these purposes:
...... to compensates for, and/or to help eliminate resistance caused by the OEM hull harness (to starter motor solenoid S terminal).
...... to prevent the possibility of current back-feed for ignition or electric fuel pump potential issues.
See ** above.
In my opinion, if all is working correctly, the slave is not necessary.

Click to expand...

Thanks again Rick. You are a valued resource.

If curious, ask them to explain why!
Yes, I did, but... They said it's because of the very high amperage of these starters that a slave solenoid helps. My thinking was that the solenoid only handled low amperage and just enabled, by closing contacts, high amperage between battery and starter.
Does your comment - "Your HTGR/PMGR replacement motor's solenoid serves two purposes......
1..... kicks the pinion gear into the flywheel ring gear, and 2.... simultaneously makes armature circuit continuity." confirm this?
When I receive the new starter I'll try API again for clarification.

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ocoocher said:

Thanks again Rick. You are a valued resource.

If curious, ask them to explain why!
Yes, I did, but... They said it's because of the very high amperage of these starters that a slave solenoid helps. My thinking was that the solenoid only handled low amperage and just enabled, by closing contacts, high amperage between battery and starter.
Well.... yes and No.
With the type of starter motor that you now have, the solenoid serves two purposes:
1...... acts as an electromagnetic servo unit that actuates the lever of which kicks the pinion gear (spague clutch/pinion gear) out into the flywheel ring gear.
2...... upon completion of the above action, the electromagnetic plunger creates the heavy amp continuity required for the armature circuit.


The armature does draw heavy amps during cranking..... sometimes as much as 200 amps.
During this event, the S terminal circuit voltage also drops. (Battery voltage can drop as low as 10.5 volts during cranking)
If there is resistance in the S circuit, then it is possible for the solenoid's magnetic coil to let go during the heavy load.
However, these solenoids have been designed for this.

Some have use the Beuler or Cole Hersee five pin relays in lieu of a slave solenoid.

Does your comment - "Your HTGR/PMGR replacement motor's solenoid serves two purposes......
1..... kicks the pinion gear into the flywheel ring gear, and 2.... simultaneously makes armature circuit continuity." confirm this?
When I receive the new starter I'll try API again for clarification.

No HTGR/PMGR starter motor today would use the old school Bendix drive.
All would be solenoid lever action.

Click to expand...