Why the heck are there 2 solenoids for the starter on these trucks?! (one on the fender and one on the starter motor itself)

 

The one on the inner fender is technically just a relay. Using that cuts down on the current that the ignition switch has to deal with...

 

Ford was transitioning from and older non-solenoid style starter, this was the cheap and quick way to make it happen till the next redesign. The one on the fender actually acts as a relay to engage the starter mounted solenoid, much like a Chrysler.

 

ha, a solenoid to activate a solenoid...way to be, Ferd.

 

It's kinda silly esp on a 90's model vehicle, but if you ever have a no start condition, it can be a bit easier to diagnose in a pinch, I guess.

 

Actually, just as the other poster said, it makes perfect sense. It spreads the load more evenly across the electrical system.

 

How does 2 solenoids in series distribute the load evenly? They both draw from the single wire from the single battery. Over engineering and extra opportunity for failure. There is 0 change in load distribution.

 

If you think about it, there is a change. It's hard to think about it when the opinion is that the engineers all suck and they do not know what they are doing. I know, hard to imagine.

I think it's foolish to put that large of a relay at the fender. Do you really need a relay that can handle at least 100A for a 10 amp load? I think not. What I have seen is that the average cube relay take less than an amp to trigger it. A starter solenoid [the ones that attach to the starter] take a good 8 amps to trigger it. Starter solenoids usually push the drive gear into the flywheel and it must overcome the spring tension to make this happen. The typical Ford solenoids, that are separate from the starter, really should have never been called a solenoid, but a relay.

So, the solenoids that are part of the starter on today's Fords probably take a good 8 amps to trigger. I suspect a fender type relay take much less. Less is better for the tiny contacts in the ignition switch.

If we all agree that the fender solenoid is a relay, then there would not be so much confusion and rocks thrown.

 

Replying to this old thread, but maybe you can help me.

I have a '97 F-SuperDuty, it's a long wheelbase (156") Standard Cab and Chassis with the behemoth 7.5L 460.
It's a rear dually, 11,000 lb. rear axle.

I thought I figured out that I had a wiring problem 2 weeks ago, and once I got the truck running, I hauled a load
for 3 hours there and 3 hours back. It sat with the ground disconnected for 2 weeks. The battery tested ok at 12.67
volts, but Napa Auto told me to bring it in and they would check it as they sometimes look ok but don't have enough
cold cranking amps. The truck only has 77,000 miles on it, as I have owned it for about 15 years and rarely use it.

I replaced the exhaust manifolds last year, which wasn't cheap in the end, so it seems like good insurance to just
replace both the upper <cough> relay and the starter/solenoid combo on the bell housing/engine/flywheel cover.

Seems like from what people are saying in this thread, it could still be a problem with the ignition.

And we can all think what we want, but this is just wrong, they should have redesigned it properly. This is the only
Ford I have. I'm ordered a rebuilt Motorcraft, I tend to buy OEM parts when possible, but what do you recommend
for the fender relay? I need this truck to be reliable. I have 5 or 6 loads of about 4,000 lbs. I need to haul. I hate to
blindly throw parts at a vehicle, BTDT...but the starter has to be the original as well as the fender solen....err, I mean
*RELAY*. That makes them 27 years old...

Alan

PS - for extra credit, why does this relay look like a solenoid?

 

Im not sure what you are asking?

If you want to replace them just cause, i wouldnt replace the fender relay just cause. if it works, it works. if it doesnt, then jump it with a screwdriver. Keep a spare in the truck if you want. pretty sure ford still makes it.

The starter solenoid, you CAN replace the solenoid on the starter.. but not as common as time long passed. But if your starter works, usually you can get it to start at least one more time with a few good wacks when it fails . not guaranteed but...

 

My understanding is that one of the big posts on the "relay" goes to battery positive, so that should always have power. The other gets power when the key is turned.

However, the symptom I see is the check engine light comes on but when I turn the key farther to get the starter, it goes dead, no power until I go out and disconnect the battery and connect it again.

I long felt there was a temperature problem with starting, but was never able to issolate it. Sometimes if I moved the terminals around on the batter I could get it to start, but nothing conclusive.

I'm pretty sure the alternator is fine as the battery is fine. So do you or anyone else know why I would get a check engine light and then go dead when starting?

Alan

 

sounds ignition switch in the column more to me. Disconnect the side going to the starter motor from the relay and crank, same thing?

 

Yes, I can test that, but need to go to the truck tomorrow. This could very well be. I had a guy rekey the door locks to the ignition about 8-10 years ago, When I bought
the truck the ignition had been replaced and there was a strange small key marked gas that opened the doors, but it was not the correct key for the Ford lock.

I wonder if he hadn't replaced all of the wires. This is an easy test and may save me on the starter and relay.

Thank you for the suggestion, I will try this tomorrow afternoon, unless I can't get down there. This could be a fairly easy fix. I think I just need a poker to get the ignition out.

 

I'm going to repeat what was said in posts 2, 3 and 8.
They were redesigning and transitioning, while producing hundreds of thousands of trucks annually, and asking suppliers, like the ones who made the fender mounted relays and starter solenoids, to keep up.
My dad worked with the same crew of 5 or 6 guys, from 1951 until 1987. That wasn't in the automotive industry, but it is an example of the way things used to be.
When production plants needed to make a change, their own maintenance mechanics did most of the work required, with larger jobs going to contractors.
Parts suppliers were working out of World War 2 era buildings that were originally built to make munitions and mechanical parts for the war.
They were redesigning the cars components in a relatively stable economy, that affected a lot of small towns.
Now, for better or for worse, developers build industrial parks, manufacturers move into them and when changes are made, the buildings are put up for sale.
It's highly unusual for anyone to stay at the same job for their entire career and lots of parts are manufactured overseas.
For decades the fender mounted relay took the inrush current of the starter motor, which creates an arc.
Arcing creates heat and voltage drop.
As cars and trucks evolved, there were more electrical components in the interior of the cars and circuit boards were introduced.
The fusible links that were tapped off of the fender mounted relay started to stack up.
The arcing of the inrush current was moved to the starter solenoid so it would have less affect on the printed circuit boards that were being fed from the hot side of the fender mounted relay.
The starter solenoid is called a solenoid because it uses electrical current to move the starter gear, so it engages the flywheel.
The fender mounted starter relay is called a relay because it uses low current circuitry to switch high current circuitry.

 

But here's the thing. That top relay is used on not just trucks, but cars from other manufacturers like VW, it seems wide
spread in the auto industry.

I have both coming. If the upper relay fixes my problem, or if I can determine that it's the ignition through what @AuroraGirl
said, I can isolate it.

Thanks for both of your help.

Alan