Starter Relay (1 Viewer)

[OKMike]

1977 FJ40 with a 1982 2F engine.

I Recently installed a new aftermarket wiring harness and a new starter. I'm new to automotive wiring and am learning about using relays. Question: Should I install a starter relay? If so any recommendations on what kind to buy?

Thanks!

 

[ibinazbass]

A starter relay is a great tool to use to reduce the load that the ignition switch has to carry. By sending the load straight from the battery, through the relay, and to the solenoid; you get less voltage drop through the circuit. I would highly recommend one. Any old 20A relay will do. Try and get one that is a kit with a mounting bracket and a pigtail.

 

[Living in the Past]

A starter relay is a great tool to use to reduce the load that the ignition switch has to carry. By sending the load straight from the battery, through the relay, and to the solenoid; you get less voltage drop through the circuit. I would highly recommend one. Any old 20A relay will do. Try and get one that is a kit with a mounting bracket and a pigtail.

Think the main voltage drop while starting is the windings in the starter which are wired to the points in the solenoid. Ignition switch only sees the load from the coil in solenoid. Put a voltage meter on the terminals of the battery and start the cruiser and watch the voltage drop while starting. Next disconnect the positive lead that runs directly to the starter solenoid from the battery then turn the the key to start. Sure you will see far less drop in voltage. Just be sure the positive wire from the battery doesn't ground out when you remove it. Nothing wrong with adding a pilot relay as there is enough less current draw over the coil in solenoid. Regardless do not think the overall voltage drop will be any less. Dropping the current draw thru ignition switch is not a bad idea. Could do the same for the heater blower motor. Sure it draws more for a lot longer time. Hook up audio that turns off with the ignition switch could also add a pilot relay.

 

[Solace in Solitude]

All true... but, adding relays, when adding or rewiring, allows you to remove “load” current from 40+ year old wiring and run it via new wiring instead.

Trigger (86) the relay from the ignition start wire, ground (85) to a good ground, run battery voltage to (30/51) and run (87) To the starter.

I like Bosch relays... YMMV

Good info below

 

[kerplunk]

Is this some kind of joke I'm not getting?

The starter has a relay built in, or a soilnoid, same concept, an electric / magnetic switch. That's why there's a large #2 sized wire coming straight off the battery to it (what would be the "input" terminal 30/51 in the picture above) and a smaller ~14 gauge wire from the ignition switch ("trigger", terminal 86 from the picture).

Why would you use a relay to activate the relay?

If all the current to the starter motor went to through the ignition switch it'd melt. It's a classic case study for why relays are used. And I've never seen a car that didn't use a relay for the starter (either built in like my Land Cruiser or external like my old F250).

 

[Living in the Past]

All true... but, adding relays, when adding or rewiring, allows you to remove “load” current from 40+ year old wiring and run it via new wiring instead.

Trigger (86) the relay from the ignition start wire, ground (85) to a good ground, run battery voltage to (30/51) and run (87) To the starter.

I like Bosch relays... YMMV

Good info below

View attachment 2445333

All true Danny. It does come to a point how much more complicated are you going to make the wiring and what point do you just go to aftermarket wiring harness. My main point was the huge draw on the battery does not go thru the ignition switch. As the post above mine points out that much current thru the ignition switch it would melt.

I personally keep the factory wiring if at all possible. Something like added that would draw more amperage would go the pilot relay as the term was used in the HVAC field. After more than a quarter century sitting on a project vehicle I have finally started to look at it. Most would say need to install a aftermarket wiring harness but I plan to repair the stock harness. From the day I bought that was always the plan. Actually looking forward to the challenge of removing all the wiring hacks and going back to stock.

 

[Solace in Solitude]

Is this some kind of joke I'm not getting?

The starter has a relay built in, or a soilnoid, same concept, an electric / magnetic switch. That's why there's a large #2 sized wire coming straight off the battery to it (what would be the "input" terminal 30/51 in the picture above) and a smaller ~14 gauge wire from the ignition switch ("trigger", terminal 86 from the picture).

Why would you use a relay to activate the relay?

If all the current to the starter motor went to through the ignition switch it'd melt. It's a classic case study for why relays are used. And I've never seen a car that didn't use a relay for the starter (either built in like my Land Cruiser or external like my old F250).

Not a joke, but, I guess, you’re not getting it

Re-read posts 2-4, above.

We’re not referring to the 2ga Battery+ to Starter wire. That doesn’t change.

The point of the additional relay is to simply move the battery voltage off of 40+ year old oem wire and the 40+ year old ignition switch, when triggering the starter solenoid.

That eliminates a couple of potential points of failure... much less likely to start a fire this way.

30/51 is fed from the battery+ and 87 goes to the starter solenoid. 85 is ground and 86 is triggered from the IGN.

I no longer have 44 to look at, but I thought the trigger source was IGN-Start. ‘78 wiring diagram shows the solenoid triggered by IGN-ACC instead.

A caveat, I didn’t consider... IIRC correctly, a GRS eliminates the coil-solenoid sure entirely. Anyone considering this for a GRS, will need to validate this.

 

[Solace in Solitude]

All true Danny. It does come to a point how much more complicated are you going to make the wiring and what point do you just go to aftermarket wiring harness. My main point was the huge draw on the battery does not go thru the ignition switch. As the post above mine points out that much current thru the ignition switch it would melt.

I personally keep the factory wiring if at all possible. Something like added that would draw more amperage would go the pilot relay as the term was used in the HVAC field. After more than a quarter century sitting on a project vehicle I have finally started to look at it. Most would say need to install a aftermarket wiring harness but I plan to repair the stock harness. From the day I bought that was always the plan. Actually looking forward to the challenge of removing all the wiring hacks and going back to stock.View attachment 2445826View attachment 2445828

I get your point, John, and certainly don’t disagree with anything you’ve said.

Having dealt with melted wires, I’m more interested in safety and trail reliability than with keeping it oem.
At least, I was, when I had 44.

 

[kerplunk]

Not a joke, but, I guess, you’re not getting it

Re-read posts 2-4, above.

We’re not referring to the 2ga Battery+ to Starter wire. That doesn’t change.

The point of the additional relay is to simply move the battery voltage off of 40+ year old oem wire and the 40+ year old ignition switch, when triggering the starter solenoid.

That eliminates a couple of potential points of failure... much less likely to start a fire this way.

30/51 is fed from the battery+ and 87 goes to the starter solenoid. 85 is ground and 86 is triggered from the IGN.

I no longer have 44 to look at, but I thought the trigger source was IGN-Start. ‘78 wiring diagram shows the solenoid triggered by IGN-ACC instead.

A caveat, I didn’t consider... IIRC correctly, a GRS eliminates the coil-solenoid sure entirely. Anyone considering this for a GRS, will need to validate this.

How much amperage does it take to power the solenoid? I always assumed it would not be much.

The starter solenoid is already acting as a relay for the starter. So you're adding a relay to the relay? (I'm really more used to mid '80 Ford trucks with a separate relay mounted 6" from the battery on the main power to the starter, where it is just a relay, nothing else)

Because when someone "new to automotive wiring and learning about relays" asks about the starter... It already has one built in. Sure, you can get more creative with it...

 

[OKMike]

Hey Guys:

I posted this a while back read the first few responses then got busy with other parts of the harness project so I haven't been back to check the forum until today. Got a chance to read through all the posts tonight. I really appreciate you all taking the time to share your advice and expertise. I think I'm tracking now.

WRT the new harness project itself--It's been slow going but I'm proud to say I've got most everything installed, and working like it should including the starter. Thanks again for your help. Without this forum I'd be lost as last year's Easter eggs.

More questions to follow I'm sure. Cheers!

--Mike