Classic Mustangs (Tech)Technical discussions about the Mustangs of yester-year.
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here's the easy schematic on starter selonoid there are 4 connectors the two outer ones (BIG cables got there)
and the two inner ones (small cables go there). The inner one's are labelled with 'S' adn 'I'
now when you call this thing a starter relay it's easier to understand how it works.
For starting you want the starter to get 12V+
As the starter sucks A LOT of amps (thing needs a lot of power) the cable is quite BIG. It is the one connected to the relay on the right hand side.
Now if we hadn't got a relay we would have to route those big things to the ingnition switch and from there to the starter. Noone wants that.
Hence the idea of a relay: The relay is an electronic switch and some of them can switch BIG power. the starter relay is one of them.
If you get a tiny bit of 12V+ to a plug at the starter relay it will connect the big 12V cable from battery directly to the starter.
This connector for activating this switch is the 'S' port (s for start)
So basically there's 12V+ going to your ignition switch. when you turn the ignition switch to start it will power a little cable connected to the switch with 12V+ that connects to this 'S' port.
Once we have 12V there the starter will get it's power.
left big connector: battery plus
right big connector: starter (there is only one connector on the starter). It get's it's minus/ground from the engineblock.
small connector 'S': ignition switch 'S' connector (goes through firewall connector)
The 4th connector ('I' for ignition) has only a simple purpose:
Factory coil is getting 7.5V during run. This is not enough for starting the engine (works fine once started, but problematic _during_ the starting process).
So when you start the engine the 'I' port gets 12V+ as well which leads to coil+. only low amps needed hence a thin cable.
This is not needed for the starter to be able to turn.
Here's the starting troubleshooting process. It's very easy to follow once you've the above said understood.
ALWAYS MAKE SURE THE CAR IS IN NEUTRAL OR PARK, as a remotely started car will move when in gear !!!!!
This is only troubleshooting the starting process (get the starter/engine) turned.
Means if you turn your key and nothing happens use this:
Tools needed: Jumpleads and big screwdriver (and a good known battery. don't waste your time and try that with a flat battery ...)
1. Make sure the engine (and starter) is grounded gets battery minus:
Take one cable of the jumplead pair and connect it:
battery minus to engineblock. Look for a blank spot you can hook it up to. The bracket that holds the alternator should do fine.
try to normally start your car. if nthis works then replace your ground strap to engine block. Or put one there if its missing
2. If it still does not work:
leave the minus cable as it is from step1 and connect the 2nd cable:
from the left (big) port to the right (big) port of starter relay
If the starter makes noise or starts to run, remove cable. Don't try to start car like that
- if nothing happens: check the cable going from right port of relay to starter. If that's good I'd say the starter is fried
- if it tried starting it does NOT tell you anything about the starter relay, but it DOES tell us: the starter is good.
make sure to try the same without the cable you connected from battery minus to engine block. if that works as well, you can do the next tests without it.
3. Test the starter relay
If you were successful on step 2
disconnect the cable on connector 'S'
hold a long screwdriver and bridge the 2 connections:
left (big) connector to 'S' on starter relay.
This way you simulate the 'S' getting 12V+. You can as well connect a cable of the jumplead from one connector to the other.
If this does not work (but step 2 was successful), I'd say the starter relay is fried. try same thing with 'I' disconnected as well, mayve some cabling issue there annoying the relay.
If it does work: starter relay, starter, ground and battery are all good (that's great news) because the rest is cheap fix.
Most people try this step as the very first one as 90% of all starting issues (aside a flat battery) is what comes next:
4. if 3 was successful the problem is:
either the ignition switch or the cabling towards it or the neutral safety switch or even a fuse.
- check all fuses
in a schematic it works like that (for automatic. manual the same just without the safety switch)
cable from battery plus to ignition switch (maybe fuse in between). once you turn the switch it gives this 12V+ to a different cable that goes to the neutral saftey switch.
When this is closed (car in park) it switches this 12V to the 'S' port.
If it's an automatic you can always check on the transmission (where this switch is located) and see if you can connect the 2 cables going there together.
If you can start your car normally with your ignition key, the problem is the NSF.
I guess this is much more detail then you wanted but I'll keep that for future reference .... it will be asked again ....
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Hi, I was hoping that someone can help us. My girlfriend and I have followed the diagram but when we turn the key on our '66 Mustang Coupe sparks start flying right at the solenoid!!! We have put in a new headlight wiring harness along with a new alternator wiring harness so we know we have the cable colors correct. Our doubt is how we have the starter connected since it sounds like the starter is ticking while the sparks are flying!!! We have the screw (ground screw?) on the back of the starter connected to the firewall. Also we have the negative terminal on the battery connected to the engine block. Should the starter ground be connected to the engine block as well?? Please help
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