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Starter Assist Relay Assembly and Install

89785 Views 1 Reply 1 Participant Last post by  Brad
***Update! MTF Member Stripmine drew up some illustrations to help with the CORRECT way to install a Starter Assist Relay. It's with his permission that I have inserted those drawings into this submission. It really shows "how to" and especially "how NOT to". My thanks to him for the use of these drawings.***

Some time ago I put together a couple threads with the instructions for installing a "Starter Assist Relay" on John Deere STX38s. Over the life of those threads I have probably e-mailed out close to 100 or more schematics and instruction sheets. There have been updates to the instructions from info and photos supplied by several members that have installed the relay on their machines, so this design, even though I posted the original, includes the submissions of others as well. Also, this was originally submitted as an addition to the JD STX38, but it has been installed on various makes and models with similar positive results.

The reason for this Starter Assist Relay is to deal with the issue that many LGTs are plagued with, the "Click, Click, Click" problem encountered when turning the key to the "Start" position. (This is not to be confused with the lighter "click" heard when turning the key to the "On" position, which emanates from the carburetor area. That is the result of the fuel solenoid plunger retracting when +12v is applied.) The clicking heard in this instance is a result of a lower voltage being applied to the solenoid, which fails to fully activate the starting process. When an older tractor was new, all the safeties, switches, connections, etc., were clean and shiny. Turn the key, and whatever voltage was contained in the battery was applied to the solenoid. Over time, connections corrode, safeties corrode, wires corrode, battery voltage diminishes, etc. So, instead of having 12.5-13v hit the solenoid when you turn the key, you may only have 8-10v. One could replace all the safeties, clean all the connections, replace the solenoid, etc., and have a machine with a starting system with like-new performance. Costs would probably run in the $100+ range, or a Starter Assist can be installed for less than $10. (Much less if you have an overflowing "junk box".)

My original install utilized a relay that I purchased from an auto supply store for about $3.50. It did not include any wiring, connectors, or other hardware. It is a relay for auxiliary lights or horns, good for approx. 30 amps. I have seen these sell for as much as $20 at some stores, so shop around if you get a high price quote. I had the extra wires and connectors around the workshop from years of "pack-ratting".

Anyway, here is a drawing of how your solenoid/starter circuit is activated as originally installed. You turn the key, 12v goes from the ignition switch to the solenoid, providing all safeties are intact and the circuit is not broken. That 12v activates the solenoid, causes it to create a bridge between the two large posts and supplying enough amperage to turn the starter, and subsequently turn the engine over. When the contacts get questionable anywhere in the circuit, the problems begin. This is where the "Click, Click" issue arises. Time for a Starter Assist Relay installation!

Illustration by Stripmine:

This first diagram is a generalized view of the starting circuit, with the safety switches shown as they would generally be arranged ( in series) in the wire between the key switch and the starter relay.

Now, when I do something, and it works, I like to keep my eyes open for a better process to accomplish the task. I know I've seen kits around where you could get the relay, wires, connectors, and maybe even a relay socket. I have yet to find one of those locally, and am hesitant to buy one over the internet as shipping will run more than the part itself. I was at Farm and Fleet a while back and ran across this kit. Less than $8. Only thing missing is the socket, but all the connectors are there, so this is a great find.

Like a kid on Christmas, I had to rip the package open, touch the parts, read the directions (even though they had nothing to do with my project), test fit the connectors, etc.

A very important part of any project is having a friend or two on hand to check your work and hide the occasional wire, pencil, or connector, just to keep you on your toes and alert to any possible missing parts. Plus, it makes the pleasure of performing the project last much longer than if you whipped it together unassisted!

OK, this is how your starting system will lay out when the starter assist is installed.

On the bottom of the relay, the prongs are numbered. You want to connect these prongs as follows:

#85 connects to the engine/frame/ground of the machine. I used a short wire and looped it back around where it was connected to the engine shroud with the sheet metal screw I had used to attach the relay near the starter.

#30 connects to a 12v power source (constant). I connected mine to the battery side post on the solenoid for convenience.

I then took the wire that ran FROM they key switch TO the solenoid and connected it to the relay prong #86 (or ran a wire from prong #86 and connected it to the wire from the key switch).

Then, lastly, a wire from prong #87 goes to the small post on the solenoid from which you removed the wire from the key switch.

Illustration by Stripmine:

This diagram, shows an acceptable place to install the new relay, in series with the safety switches, so that their function is not defeated.


Once again, you MUST get another friend or family member to check your work. They have to check it, top to bottom, front to back, looking for that elusive part or wire that you missed or forgot to connect.

Anyway, now that you have the relay installed, here is how it works. As long as all safety requirements are met (seat, neutral, brake, blades, etc...), when you turn the key, a voltage will be applied to the relay (instead of the solenoid as in the original design). Since the solenoid takes 12v. approx. to activate the starting system, and the relay will be activated with as little as 6v, a circuit is made inside the relay. By doing that, the relay will supply the voltage contained in the battery to the solenoid, thus activating it and causing the starter to turn. Now, if your battery is low or weak, you could still encounter the same issue, but providing your battery is charged and contains sufficient voltage, you'll be in business.

Now here is the important part! This is a diagram of the IMPROPER way to install a Starter Assist Relay supplied by Stripmine! This type of installation will bypass the safeties and that is something you do NOT want to do. It's an accident or injury waiting to happen:

This third diagram, shows how the safety loop is defeated, if the new relay is installed and wired either directly off of the key switch, or on the "upstream" side of the safety's.

Out of my purchased relay kit, these will be the parts left over from the Starter Assist Relay install. I'll throw them in my parts box for the next project that comes along!

OK, these are the photos of my finished project. This is on the a John Deere STX38 that I used to have. From the time I installed the relay until I let it go, I didn't have a single "Click" when turning the key. It always activated the starter the engine spring to life!

I have since given the tractor to my daughter and her husband. I imagine they will get many years of use out of this tractor, and hopefully no starting issues related to the low-voltage symptoms that once plagued this machine.

Good Luck with your project, and if you have ANY problems or questions, don't hesitate to ask via PM or e-mail. if you need a schematic and a .pdf of the project, please include your e-mail address.
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