Installing a relay on the starter

[Hermit Scott]

I need to install a starter button. I have been starting it by a small bolt across the starter to the solonoid. I think I am ready for the luxury of a starter button.
I looked up relays, most of them say 5 pin relay.
Is the diagram correct? Where does the fifth pin go? How many amp relay do I need?

Edit:I changed the diagram.

 

[Dan Johnson]

Hermit...

go to Radio Shack and have them find their 30 amp relay with the 12 volt coil (should be under $10--don't have the part number handy but other replies might). It has standard 1/4" male slip-on connectors. It is a single pole single throw momentary on when the relay coil is energized. Add a 30 amp in-line fuse in the power run off the battery plus at the starter to one of the relay contacts (point or arm) in your diagram.

Any waterproof momentary contact device (ie. doorbell button) will serve as the "starter button" if you don't have one. For more security and locking protection a simple on-off key switch could be added in the starter button wire run.

The relay diagram schematic isn't correct in that the electromagnetic coil is wired to ground at one end and at the other to the starter button then to power plus (which can be taken off the battery lead to the starter as shown). The connection between the starter positive and the solenoid runs through the arm and point in the relay.

Your fifth pin may mean that the relay you're looking at is a SPDT one (Single Pole Double Throw). One side may always be on while the other is always off. Momentary energizing of the coil reverses this.

JUST REMEMBERED I HAD A PIX FROM SOMEONE'S INSTALLION OF THIS SET-UP, COMPLETE WITH THE SHACK'S PART NUMBER!

 

[Hermit Scott]

I changed the diagram. Is that correct?

 

[Dan Johnson]

Hermit...

look again as I've added a pix I remembered I had.

Yep, it looks like that revision will work!

 

[Hermit Scott]

What is the 5 pins for? 2 high current, 2 low current and the fifth?
Sorry I didn't read your post carefully. I see what you have written about the 5 th pin.

 

[Timo42]

That is what is known in the bidness as a Bosch relay, pins 85 and 86 go to the coil, 30 and 87 go to the load, 87a is the normally closed terminal, usually there is a wiring diagram cast into the side. No offense to Dan, but I am less than impressed with the quality of RS parts, and that isn't a sealed relay. For long term health a sealed relay with a weatherpack connector is the way to go. GM used lots of them, you can get the connector and relay at a dealership, don't have the #s handy, Painless wiring sells the same thing as a kit for about $45, with a circuit breaker http://www.jegs.com/p/Painless/Painless-Weatherproof-Relay-Kits/756494/10002/-1 they are using it as a fuel pump relay, you would hook 85 through the starter button to 12v, 30 to the battery cable at the starter stud, 86 to ground and 87 to the starter terminal. You could find the relay and pigtail at a junkyard under the hood of many 90's to current cars.

 

[Hermit Scott]

If I use a relay like the one in the pic, it's getting everything encased in epoxy.
$45 is a little steep for my cheap blood. But thank you for the link. I'd like to find something automotive and do the epoxy thing to it.

 

[Timo42]

Hermit, then go to the selfserve wrecking yard with a pair of sidecut pliers and you will find all you need for the price of admission, no epoxy necessary, most of what you will find will be rated at 30 to 40 amps, and if you get a couple of spares, you wont have to worry if they are used and the oem stuff is a lot more durable than the cheap knockoffs I am seeing now.

 

[Hermit Scott]

The relays I have seen in cars were in a fuse box. They looked alot like the one in Dan's pic but they plugged in.

 

[Timo42]

mid 90's Cadillac, firewall or left front fenderwell, chevy trucks, near or under fusebox, firewall, they usually have 2 10ga wires on the load side, used for starter, theft, abs and hvac blower relays. If you want to pm your address, I'll mail you one, I have a few saved.
Tim

 

[Hermit Scott]

You are the man! my address is
Scott Turner
2424 Broadway
San Antonio Tx 78215
That is the Midas shop I live in. I already looked through the inventory, I didn't find any relays. Google map it. I live in the warehouse connected to the back. Pretty weird but that's the situation for now.
I would like to paypal you for your trouble or I can send it to you snail mail.

 

[Dan Johnson]

Tim...

thanks for the info on the automotive source. It's been many years since I prowled a junk yard! Your specifics are a great help.

Given the price of the RS relay, I'll take my chances to see how long it will last. Can't disagree with the quality issue either.

Didn't have the pin-out numbering in front of me either (it's standard for relay terminals) so didn't want to give out bad info.

 

[Timo42]

Hermit, found a brand new relay of the bosche type in the junk box, but must have put all the used ones with the connectors somewhere else.:cry: Found another style of weatherpack relay connector, but no relay to match. One way or another I will have one on it's way in a day or two. Mebbe I'll come across the missing taillight for my 912 while I am looking.:dance: GM part number for the relay is 12034544. When I find the connector I will see if I can get the number for that too.

 

[Hermit Scott]

Thank you Tim. Did you disassemble your porche? Are you that guy with a dozen unfinished projects all over the house? Just Joking, that's all of us.

 

[luvitt]

why is the relay necessary? I bought a new relay when i rewired my ignition, couldnt figure it out and left it off! engine starts everytime. whats the relay do that the key switch doesnt? a relay is just a switch right?

 

[RichH]

why is the relay necessary? I bought a new relay when i rewired my ignition, couldnt figure it out and left it off! engine starts everytime. whats the relay do that the key switch doesnt? a relay is just a switch right?

The starting torque with a 'starter' creates a momentary high amperage draw as the starter begins to turn, usually more amperage than can be handled in a 'keyswitch'. You'll soon be burning the keyswitch thats wired into the BAT circuit because its not designed to carry the momentary high amperage.

 

[Timo42]

Yeah, Hermit, I'm that guy, been rebuilding the 912 for 10 yrs on and off, the wife calls it the Push, should be burning gas for the first time in 10 yrs next week. :dance:
Brobins, the relay shortens the length of the circuit to the solenoid from the battery, the longer the wire the more voltage drop. the relay needs a lot less current to close than the solenoid, and is more tolerant of low battery voltage, dirty contacts and long wire runs. You can also run a smaller guage wire to the switch if necessary.
Tim

 

[Ron20324]

The starting torque with a 'starter' creates a momentary high amperage draw as the starter begins to turn, usually more amperage than can be handled in a 'keyswitch'. You'll soon be burning the keyswitch thats wired into the BAT circuit because its not designed to carry the momentary high amperage.

Correct me if I'm wrong, but I don't believe the keyswitch would carry any more current than a relay would. It only handles the starter solenoid current, not the starter itself.

 

[RichH]

If the keyswitch is in the solenoid primary circuit (thin wire), then yes you are correct; however, if its placed in the secondary circuit (thick wire) then the keyswitch wont be able to take the load.

 

[Timo42]

The solenoid draws far more current than a relay because it is pulling the bendix as well as closing the contacts, don't have the numbers in front of me. Using a relay in the starter solenoid ckt has become almost universal in the automotive world in the last 10 yrs, several mfgs have even had recalls to retrofit a relay. Chevy cavalier and Hyundai come to mind. I am adding one to the starter ckt on the Push, hotrodders commonly use them.