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Old 01-15-2012, 05:52 PM   #1 (permalink)
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Default Deleting Old Solenoid with Starter Upgrade

I'm thinking of upgrading to a newer PMGR starter with the solenoid on it in my 70 Mustang and then removing the old solenoid for a cleaner look under the hood. Any reason to keep the old solenoid? Can I connect the "I" terminal wire right to the starter terninal that's hot when starting?
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Old 01-15-2012, 09:32 PM   #2 (permalink)
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I have a modern 5.0 starter and it still requires the solenoid on the inner fender wall.
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Old 01-15-2012, 09:45 PM   #3 (permalink)
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Yes you can, I like having the solenoid up there for ease in connecting a remote starter switch when finding #1 cyl, or dropping in a distributor. However, you can do what you want
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Old 01-15-2012, 09:55 PM   #4 (permalink)
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My '95 only has the solenoid on the starter, but from my Internet readings I have done, the cars equipped with them from the factory have a diode or something built into the electrical system.
My understanding is that without the device, once the car cranks, for just a split second, the flywheel is turning the starter and then the starter is producing voltage and creating a "run on" condition where the starter will run for half a second after you let go of the key.
Now being the electronics technician I am, and owning a set of '95 Factory Service Manuals, I will get to the bottom of this when I start my wiring job.
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Old 01-16-2012, 01:15 AM   #5 (permalink)
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That's odd. When most people convert to the modern starter, they move the starter power cable from the switched side of the old solenoid over to the battery cable side. The new starter now gets 12v to the new solenoid all the time. The old solenoid just acts like a relay for the switch wire. If I replaced the old soleniod with a small relay for the switch wire, it should do the same thing. I can't think of how this would effect the starter staying engaged from any voltage it generates by spining though.
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Old 01-16-2012, 10:40 AM   #6 (permalink)
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I don't know all the how's and why's but I do know that I've swapped a couple of PMGR starters into older Fords. Twice I attempted to make and end run around the old solenoid and both times the starter would "hang" eaxactly as ScottsGT described. Thereafter I just wired them in with dual solenoids though I've heard that folks have wired them in the "GM" way and experienced no problems like I did. I'm sure using a diode would do fine as a way to eliminate the extra solenoid. My wife's old Explorer and my current F150 both had dual solenoids from the factory. Good enough for OEM, good enough for me.
That my '67 still has an external solenoid doesn't bother me at all since I have moved it and the battery to the trunk. I understand wanting to eliminate such a solenoid, it's not an attractive underhood feature.
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Old 01-16-2012, 11:03 AM   #7 (permalink)
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According to a Ford powertrain engineer I spoke with a couple of weeks ago, The fender mounted solenoid is required on older cars not originally equipped with the PMGR starter, because the ignition switch is not designed for the amp load from the PMGR starter solenoid, and may burn out over a period of time. It will work for awhile but to avoid problems, just use the fender mounter solenoid.

There is also a big difference in solenoids, if you are using a MSD or any ignition that requires a full 12V, the one you need is from a FI injected Mustang, a '92 Mustang solenoid has a diode that will prevent back feeding the electrical system plus it has one small terminal for the start wire from the ignition switch, the other small terminal is deleted.

Buy your solenoids only from your Local Ford parts dept, they are much better quality than just about any aftermarket solenoid.
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Old 01-16-2012, 02:10 PM   #8 (permalink)
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Quote:
Originally Posted by craigrad View Post
That's odd. When most people convert to the modern starter, they move the starter power cable from the switched side of the old solenoid over to the battery cable side. The new starter now gets 12v to the new solenoid all the time. The old solenoid just acts like a relay for the switch wire. If I replaced the old soleniod with a small relay for the switch wire, it should do the same thing. I can't think of how this would effect the starter staying engaged from any voltage it generates by spining though.
Absolutely correct, as long as the new starter relay can handle the amperage of the PMGR solenoid.
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Old 01-17-2012, 12:01 PM   #9 (permalink)
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I wanted the "clean" look as well, I also have the battery in the trunk.

I installed a small (fan style relay) under the dash to minimize current in the ignition switch) the contacts of this relay drive the solenoid on the mini starter.
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Old 01-17-2012, 12:01 PM   #10 (permalink)
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I wanted the "clean" look as well, I also have the battery in the trunk.

I installed a small (fan style relay) under the dash to minimize current in the ignition switch. The contacts of this relay drive the solenoid on the mini starter.
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Old 01-18-2012, 10:40 AM   #11 (permalink)
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I wanted the "clean" look as well, I also have the battery in the trunk.

I installed a small (fan style relay) under the dash to minimize current in the ignition switch. The contacts of this relay drive the solenoid on the mini starter.
And here's the reason to have a second solenoid in the trunk when using a trunk mounted battery. This keeps the cable from the battery to the starter dead at all times except when cranking.
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Old 01-18-2012, 06:50 PM   #12 (permalink)
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And here's the reason to have a second solenoid in the trunk when using a trunk mounted battery. This keeps the cable from the battery to the starter dead at all times except when cranking.
I ran mine without the solenoid in the trunk for a year or two and then added one when I added a battery cutoff switch.

I don't have my mustang note book with me, but I seem to recall that the +12V from the trunk solenoid is now connected to the starter side of the PM starter solenoid. i.e. the trunk solenoid is now switching the 12V to the starter.
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Old 01-18-2012, 08:09 PM   #13 (permalink)
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So the diode goes where?
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Old 01-18-2012, 08:49 PM   #14 (permalink)
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So the diode goes where?
Between the small lug and big lug on the PMGR solenoid, in that direction. This keeps the "generated" current from traveling back to the energizing lug on the solenoid.

The "proper" way to eliminate the fender-mounted solenoid would be to run the positive battery cable to a standoff where it can feed the accessories that were connected to the battery side of the solenoid, then an extension cable from there to the PMGR big lug. The wire that went to the "S" terminal on the solenoid would then go to the small terminal on the PMGR. If you are still running points and a resistor wire, you're screwed as you now have no switched 12V source for your coil.

If you have a trunk-mounted battery you still need to get power to your feeds. I'd install one of the following mounted by your battery box then run cable directly to the starter then up to a standoff for the feeds.

Fully Electronic Master Battery Power Cutoff Switch.

For those who don't like the electronic approach to battery master switches you can run a universal cable with handle to the switch and pull to disconnect.
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Old 01-18-2012, 09:51 PM   #15 (permalink)
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That's where I was thinking.
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