F-150 starter circuit

[billr]

Make

Ford

Model

F-150 2WD

Year

1999

Miles

unk

Engine

4.2L V-6 auto trans (4R70W)

The typical sometimes "no-crank" problem. It is probably in the range switch (auto trans) because the shifting lever is rather finicky. However, in preparing to be able to jumper power to the starter solenoid, to force cranking, I notice that this beast has two high current contactors. One down on the starter itself, a solenoid that both engages the drive gear with the flex-plate and connects main power to the motor. But, there is also a high current contactor (heavy cables in/out) up on the firewall. I suspect that contactor is in series with the starter solenoid. Anybody have schematics that show both of those power relays?

 

[Mobile Dan]

Looks like the "high current contactor" on the firewall connects B+ to the trigger wire for starter.

 

[billr]

OK, I see that. It is a big relay, with battery-size cables to power that solenoid on the starter. Seems kind of odd, since the solenoid only needs about a #16 AWG wire, but it is a Ford design... I should not complain, it is far easier to get to that relay on the firewall than the starter if I need to force cranking; especially out on the road and in the rain! Won't even need a wire, just a key or coin to bridge the two studs on the relay.

 

[Mobile Dan]

That solenoid may also function to "cut power to some stuff" while cranking and reconnect power to that stuff when solenoid internal contact returns to Off position.

 

[billr]

The schematic you posted shows it as a simple SPST relay, and that is what it looks like. It looks the same as Ford was using from about 1930 and on, when they hadn't adopted the gear-engagement solenoid design yet. Maybe they had a vast supply to use up?

More Information for WVE 1M1090

 

[nickb2]

It looks the same as Ford was using from about 1930 and on, when they hadn't adopted the gear-engagement solenoid design yet. Maybe they had a vast supply to use up?

That sounds about right bill.

Things have evolved since then, but going back to this design, much have cost ford a lot of money or all that copper for all those yrs. Wonder who was the bean counter in that one.

 

[billr]

OK, back to the root problem. The shifter cable had broken strands that were bunched-up and making the cable hard to move as well as sometimes restricting its travel. Fixed.

 

[nickb2]

The shifter cable had broken strands that were bunched-up and making the cable hard to move as well as sometimes restricting its travel. Fixed.

awesome, this is a fixed

 

[nickb2]

I like root problems, it is safer for me in my brain space.

My son is ocd, I am ocd, my greek gf suffers from chronic thyroid gland things I will never understand.

Life is what it is. And my job is to be better at it than all of them. Cuz if I dont check the chessboard, things go south quick, much like usa on trumps watch


And no, I am not a class a politician, I am just a class a tech.

Hugs, and kisses to your miss R, she is lucky to have you.