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Dumb electrical question #2468682
03/19/18 06:03 PM
03/19/18 06:03 PM
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madscientist Offline OP
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Can anyone tell me how to determine wire size for a wire running from the positive side of the battery to the main stud on a Ford starter relay? I guess a Chrysler relay would require the same.

Also how do I determine what wire size to use on the other stud that runs down to the starter?

Do those switches actually draw current? I'm electrical ignorant. I have a guy telling me I need 1 gauge wire on both terminals, but that seems way overkill. The only thing that circuit does is make the starter engage.

Any help will help.

Thanks


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Dumb electrical question [Re: madscientist] #2468698
03/19/18 06:40 PM
03/19/18 06:40 PM
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Actually, the large studs carry the current to run the starter - 125~200 amps - depending on engine, starter etc. The solenoid simply connects the two to make the starter run. I use 2ga. on race cars, but I also use fine strand welding cable, use good parts and make sure everything is in good shape and I'm anal about weight and keeping the cable length to a minimum. I don't have any issues and other folks believe that's too small. 1ga. should be OK, but I wouldn't call it overkill. Some folks will recommend 0, 2/0, or even larger. I would maybe bump it up a size from 2ga. in a street car with some accessories, especially if the battery is in the trunk.

The smaller studs actuate the solenoid. That's a low amp circuit.

Last edited by CMcAllister; 03/19/18 06:44 PM.

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Re: Dumb electrical question [Re: madscientist] #2468700
03/19/18 06:41 PM
03/19/18 06:41 PM
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crackedback Offline
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Depends on run length.

The factory cars ran a 10ga wire from starter relay to solenoid stud.

The main cable... BIG!!! I never run anything smaller than a 1/0 on the starter main power cable. Don't care what race car builders or the kits at summit have. Bigger is better for that cable, same for the main grounds.

Re: Dumb electrical question [Re: madscientist] #2468702
03/19/18 06:49 PM
03/19/18 06:49 PM
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Thanks guys.

We have a big cable to the big stud in the starter. My question is I guess...how many amps does the starter draw, not to crank the engine, but to engage the drive gear?

The little stud just engages the starter and the big stud actually turns the starter.

Do I have that correct? If so, that little stud can't draw anywhere near 100 amps can it?

That's what's causing the confusion. Everyone thinks those wires need to be the same size as the stater cable.

I hate electricity.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Dumb electrical question [Re: madscientist] #2468713
03/19/18 07:22 PM
03/19/18 07:22 PM
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If you don't have points anymore, and you are using a ford fender mount style solenoid to power the starter, there will be only 3 terminals used on the ford solenoid. A big one to the battery, a big one to the starter, and a little one to activate the solenoid. That little one can be 18 or even 22 gauge, it only draws 1.5 amps. The big ones can be anywhere from #4 to #00, like others have said, depending on the length and the load. If weight matters, use the thinnest that will do the job.

Edit: SO you are using the ign switch to activate the ford solenoid and the power from the ford solenoid to the mopar starter right? SO you can use 18 g from the ign switch to the ford solenoid. A fat cable from the ford solenoid to the big stud on the mopar starter. Run a 14 g jumper wire from the big 12V stud on the starter to the little stud on the mopar starter.

Last edited by Hemi_Joel; 03/19/18 07:29 PM.

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Re: Dumb electrical question [Re: madscientist] #2468714
03/19/18 07:22 PM
03/19/18 07:22 PM
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My Dad was an electrician all his life and he hated car wiring.


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Re: Dumb electrical question [Re: madscientist] #2468720
03/19/18 07:30 PM
03/19/18 07:30 PM
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If you are using the ford solenoid, you connect the small terminal on the starter to the large terminal on the starter. The ford solenoid will now "decide" when the starter spins.


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Re: Dumb electrical question [Re: TRENDZ] #2468723
03/19/18 07:33 PM
03/19/18 07:33 PM
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Napa also carries a very nice heavy duty solinoid for when that one burns out and let’s you down. A little more money but well worth it.


1970 Duster
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422 Indy headed small block
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Livin and lovin life one day at a time




Re: Dumb electrical question [Re: madscientist] #2468724
03/19/18 07:35 PM
03/19/18 07:35 PM
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Thank you all.

Unfortunately, I'm working on a Pontiac that has points (trying to get the wonder to ditch those) and he installed a mini starter so he needs the Ford relay.

There are people telling him he needs 1 or 0 gauge wires just to run the solenoid. I thought that was overkill.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Dumb electrical question [Re: pittsburghracer] #2468726
03/19/18 07:36 PM
03/19/18 07:36 PM
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Originally Posted By pittsburghracer
My Dad was an electrician all his life and he hated car wiring.


That makes me feel better. Seems to me like it's way more complicated than it needs to be.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Dumb electrical question [Re: madscientist] #2468757
03/19/18 08:35 PM
03/19/18 08:35 PM
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Originally Posted By madscientist
Thank you all.

Unfortunately, I'm working on a Pontiac that has points (trying to get the wonder to ditch those) and he installed a mini starter so he needs the Ford relay.

There are people telling him he needs 1 or 0 gauge wires just to run the solenoid. I thought that was overkill.



Maybe hes getting confused. Mopar relays use around 10 gauge to activate their relays. Ford relays use Even a smaller gauge wire to activate them, more like 12/14 gauge wire.

So Bull on the 1 or 0 gauge to activate a Ford relay or any Other car relay for that matter. Now on the Current side, different matter.

Re: Dumb electrical question [Re: madscientist] #2468763
03/19/18 08:59 PM
03/19/18 08:59 PM
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With points, there is an additional small terminal on the ford solenoid or the R terminal on the GM starter mounted solenoid that you connect to the + side of the ignition coil with 14 gauge wire to bypass the resistor during cranking. On most GM's there is a resistor wire, not a ballast resistor. On a points era GM starter, it will have 2 small terminals, marked R and S. The solenoid that is mounted on a GM starter pulls the starter pinion gear into engagement with the flywheel, as well as making the electrical contact for the starter, So it probably draws a bit more current than the ford solenoid. So connect that S terminal to the big stud that receives power from the battery (via the ford solenoid in this case) with a 12-14 gauge jumper wire.


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Re: Dumb electrical question [Re: madscientist] #2468934
03/20/18 03:52 AM
03/20/18 03:52 AM
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Not a dumb question, and actually somewhat hard to answer.
Wire size has several variables, with the amount of current it needs to carry as the main one. Current causes heat and heat increases the wire resistance, and the resistance causes voltage drop. Increasing the length of wire increases to resistance also. There is also a current de-rating for applications where the wire is heated from the engine heat.

If the Battery cable from the battery to the solenoid, and from the other solenoid post to the starter, and the battery ground cable are less than 10' total, you could use common 4 AWG battery cables and have an acceptable 3% Voltage drop at 100 Amps.

If you are doing something with long cable lengths like a trunk mounted battery, or the starter pulls more current (than 100 amps), or you want even less of a voltage drop at the starter, then you should use larger diameter cables.

Re: Dumb electrical question [Re: madscientist] #2469181
03/20/18 03:36 PM
03/20/18 03:36 PM
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On your deal the Ford solenoid will activate the Mopar solenoid so the current draw on the first solenoid is twice what it would be with one whistling work
AKA aside, use a 12 or 10 gauge wire to the Fort solenoid input battery side and a 12 or 14 gauge on the output side down to the Mopar solenoid with a 16 or 18 gauge trigger wire to the small terminal on the Ford solenoid up

Last edited by Cab_Burge; 03/20/18 03:38 PM.

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Dumb electrical question [Re: Cab_Burge] #2469185
03/20/18 03:41 PM
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Originally Posted By Cab_Burge
On your deal the Ford solenoid will activate the Mopar solenoid so the current draw on the first solenoid is twice what it would be with one whistling work
AKA aside, use a 12 or 10 gauge wire to the Fort solenoid input battery side and a 12 or 14 gauge on the output side down to the Mopar solenoid with a 16 or 18 gauge trigger wire to the small terminal on the Ford solenoid up



Thanks for the responses. When I get back over to work on it, I'm going to move the thing closer to the battery and use a bigger gauge wire just to keep the owner from losing his mind.

That is IF he doesn't work on it any more before I get there.

BTW, it's a Pontiac Cab, so only the one solenoid.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Dumb electrical question [Re: madscientist] #2469353
03/20/18 08:27 PM
03/20/18 08:27 PM
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You don't run two wires from OEM relay to trigger the solenoid at starter and ford relay.

One trigger wire from OEM mopar relay to ford relay. Or put a newer relay in the line and attach NSS to it. No more OEM relay... Had to do this on a friends car because of the way it was wired.

The starter gets a jumper from main stud to solenoid stud if it has one. It's only hot when the relay at rear is fired through the main cable.

Re: Dumb electrical question [Re: madscientist] #2469492
03/21/18 12:50 AM
03/21/18 12:50 AM
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Originally Posted By madscientist
Originally Posted By Cab_Burge
On your deal the Ford solenoid will activate the Mopar solenoid so the current draw on the first solenoid is twice what it would be with one whistling work
AKA aside, use a 12 or 10 gauge wire to the Fort solenoid input battery side and a 12 or 14 gauge on the output side down to the Mopar solenoid with a 16 or 18 gauge trigger wire to the small terminal on the Ford solenoid up



Thanks for the responses. When I get back over to work on it, I'm going to move the thing closer to the battery and use a bigger gauge wire just to keep the owner from losing his mind.

That is IF he doesn't work on it any more before I get there.

BTW, it's a Pontiac Cab, so only the one solenoid.

It sounds like your going to have to use a lot larger wire size to feed the starter motor through that Ford solenoid instead of activating the stock Pontiac solenoid work
How are you going to engage the Bendix drive on the starter without using the stock Pontiac solenoid to do that work confused


Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)
Re: Dumb electrical question [Re: madscientist] #2469499
03/21/18 01:07 AM
03/21/18 01:07 AM
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This all seems confusing. On the starter I put a jumper wire from the small to large terminal, then used a ford type solenoid mounted to the firewall. Main hot cable from the battery to one large terminal and the same size cable on the other going to the large starter terminal. 14 ga. wire from the starter switch to activate the ford type solenoid .


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Re: Dumb electrical question [Re: Cab_Burge] #2469501
03/21/18 01:10 AM
03/21/18 01:10 AM
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Originally Posted By Cab_Burge
Originally Posted By madscientist
Originally Posted By Cab_Burge
On your deal the Ford solenoid will activate the Mopar solenoid so the current draw on the first solenoid is twice what it would be with one whistling work
AKA aside, use a 12 or 10 gauge wire to the Fort solenoid input battery side and a 12 or 14 gauge on the output side down to the Mopar solenoid with a 16 or 18 gauge trigger wire to the small terminal on the Ford solenoid up



Thanks for the responses. When I get back over to work on it, I'm going to move the thing closer to the battery and use a bigger gauge wire just to keep the owner from losing his mind.

That is IF he doesn't work on it any more before I get there.

BTW, it's a Pontiac Cab, so only the one solenoid.




It sounds like your going to have to use a lot larger wire size to feed the starter motor through that Ford solenoid instead of activating the stock Pontiac solenoid work
How are you going to engage the Bendix drive on the starter without using the stock Pontiac solenoid to do that work confused



I can't remember all the details at the moment. The car is 3 hours away. This is a royal PITA because I'm not there to wipe his nose and hold his hand. Every time he works on it I have to undo what he does and redo it.

I think I'm going to sell his tools.

The funny thing is the battery isn't charging and somehow he thinks it's in the starter wiring. I've looked over the factory wiring diagram and don't see what he sees.

So, evidently, he can't read a wiring diagram. I know for a fact he can't read a map either. We rode dirt bikes together for years and many times he read the map wrong and got us into the suck.


Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
Re: Dumb electrical question [Re: rowin4] #2469508
03/21/18 01:21 AM
03/21/18 01:21 AM
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Yes it seems its getting quite confusing. A solenoid has a high amp current/load side and a low amp trigger side. Trigger side equals small wire amp needs, load side equals large wire amp needs. Simple as that.

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