Starter relay

[donm]

Can somebody whose done this before post a simple diagram on how to add a relay to the starter? I've already added relays for the headlights using a kit I got from IAP and I wanted a kit to do the starter but haven't been able to find one. I'm sure I could do the work myself if someone can show me the best way to do it. TIA.

[spider2081]

Email me I might be able to help

flyme194@gmail.com

[SteinOnkel]

I did this a couple of weeks ago.

Step 1: find the wire going from the ignition switch to the starter. You can beep it out with a multimeter or use the ghetto method of unplugging wires on the back of the switch one by one and cranking the car until it doesn't crank anymore.

Step 2: Find a place for the relay. I recommend the relay tray underneath the passenger side dashboard. There's a bunch of relays in there, a lot of them are for emissions items that don't work anyways. And they are really nice metal, Bosch relays. No reason not to use them.

Step 3: Run a wire from the ignition switch terminal to the relay coil (pin 86)

Step 4: Find a good ground wire (use your multimeter) or install a new one and connect to relay (pin 85)

Step 5: Run a wire from the Relay (Pin 87) to the starter.

Step 6: Run a fused wire from the battery to the Relay (Pin 30)

That's it, you're done.

Bonus Points: Install Valucraft Stoplight Switch DR496VC on your clutch pedal and wire it to interrupt the ground circuit of the relay. That way you can only start the car with the clutch pedal pressed. Fits plug & play.

[aj81spider]

Here is the diagram I used to put ignition switch relays on my 1981 a few years ago. You can delete the two relays that aren't used for the starter if you don't want to completely unload the ignition switch (although I recommend it).

PM me if you have any questions. I also have more extensive diagrams that show before wiring that I can send you if you'd like as well.

[scrapironchef]

Steinonkel laid it out pretty well above in terms of what has to be done but I question the idea of putting it under the dash. If you mount it under the hood you have easy access to all the necessary wires and don't have to lay on your back in the footwell. Use a fused relay socket or fused relay and this is a piece of cake. You can pull the power you need from the starter post, ground to the fender pod, the trigger wire comes off the starter and goes to the relay and you install a new wire from the relay to the starter. This can all be done standing up.

I actually put one of these - https://www.amazon.com/12-Slot-Relays-H ... 82&sr=8-13 - under the hood. It holds the starter relay, headlight relays, and a fuel pump relay with associated fuses in an easy to service location. Most of the work was don at the bench and just plugged in when I was done. I just cut the existing headlight lines and crimped on connectors, same for the starter line.

[donm]

This is great info but should I use a particular size wire for each of the terminals from the relay?
Also, which wire (color) from the ignition switch should I tap into?

[SteinOnkel]

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

[spider2081]

https://www.wirebarn.com/Wire-Calculator-_ep_41.html

Thanks this is a great tool.
I think its important to note that current draw and wire length are not the only factors in determining wire size. The temperature the wire operates in,how many strands of wire make up the stranded wire, the material type, and especially the type of load. For many loads found in a car or boat such as lighting, electrical motors and solenoids a general rule of thumb is double the constant current when selecting wire size and switching devices. This is because when the circuit is first turned on there is a huge short duration surge current that greatly surpasses the constant current. It is the surge current that is responsible for the "dreaded click" when engaging starter solenoids.
Using a wire chart one might expect a # 18 wire is sufficient for the starter solenoid circuit. Fiat uses a # 12 wire which is more than twice a # 18's size. Fiat used a number 10 wire to feed the ignition from the battery and a number 12 wire to go from the ignition switch to the solenoid.
So I'm thinking to relay the starter solenoid circuit one should use a relay whose contact rating is 40 amps and contact wires at least size 12.
Interesting read: https://www.westmarine.com/WestAdvisor/ ... Tech-Specs

[SteinOnkel]

Someone unaware of surge currents should be touching the starter circuit. As for the wire itself, buy it from a reputable source, i.e. wirebarn. Not amazon. Not Home Depot etc.

That being said, the starter solenoid does not really draw as much as you would expect, surge current or no. Most of the load is from the starter itself. On my other car I've got an interrupt circuit for the starter solenoid and it runs on a 10Amp fuse. Works great.

[donm]

Well, after hooking everything up per the Board's help, I was hearing the relay click as soon as I hooked up the power lead, even with the ignition off. I knew that couldn't be right so checked my wiring again (Thanks, Tom) and saw that somehow I had mixed up the wires to terminals 86 and 30. I corrected my "mistake" and everything then worked as it's supposed to.

But then, just checking a spare relay I had, I swapped it into the socket and had the original problem back!. Turns out that on the two relays I have terminals 86 and 30 are in opposite locations! They're both 30 amp 12 volt automotive relays. Is one of these relays an oddball? Or are the pin locations on a relay something to pay attention to? I had assumed they would all have the same pin layout.

[aj81spider]

I learned something today. There are apparently two types of relay (A and B) where the pin 86 is swapped. Here are a couple of informative links:

https://www.12voltplanet.co.uk/relay-guide.html

https://www.hagerty.com/articles-videos ... ays-part-2

[spider2081]

I learned something today. There are apparently two types of relay (A and B) where the pin 86 is swapped. Here are a couple of informative links:

I too learned something today. I knew not everything that looked like a Bosch cube relay was what it appeared. I didn't know the A and B type relay and the A, B identification existed.

Thanks for the posts and links.

[RRoller123]

Is it just the physical positioning of the terminals that is different, or is the "standard" labeling of what the terminals actually do also different?

[aj81spider]

Given that I just learned there were two types yesterday you should take this with a grain of salt, but my reading is that the terminals perform the same functions they are just positioned in different places.