I just bought a 1990 F150 4WD, manual transmission w/ 300 CID I-6. The PO had just replaced the clutch slave cylinder and in doing so he broke the line running from the reservoir to the slave (it has the internal/concentric type hydraulic clutch), so there is no fluid in the clutch. It hasn't been started for several months. It was my intention to just get it running and speed-shift (without clutch) her home where I have the facilities to work.

Once I got the key cylinder replaced (PO had lost the key), I found it will not engage the starter. I am thinking it may be because of the clutch interlock switch. Does this switch require hydlaulic pressure to close? Or is it a purely mechanical linkage? Can anyone tell me where it is located and how to "jump" it?

The ignition switch actuating rods (upper and lower) have come apart, so I am manually operating the ignition switch by means of the lower rod. Troublesome, but workable.

Also, is there any other interlock that requires the engine to be in neutral to start? In older trucks when I have no clutch authority, I just pop her in neutral at stops and turn off the engine. To go I put tranny in first and turn the key to start in gear; then speed-shift through the gears. I am thinking this might not be possible in these later models.

Now I am leaning toward towing her home, but still interested in your answers.

Any advice/opinions are appreciated.

 

Above the gas pedal is the clutch start switch. Jump the 2 red/blue wires to bypass it. Not sure if that trans will speed shift or not, I tried it on my 92 once and it wouldnt shift. Ive got an old toyota truck you can drive all day with no clutch and never grind a gear.

 

The only thing I see "above the accelerator pedal" is a small white box with at least 5 wires going into the back of it. They are from what I can see: red, green, broen, yellow, and blue. Is that it?

Are you supposed to pull the connector and jump those wires, or jump them with the plug installed? Thanks.

 

One thing you could do is lift the hood and on the pass side inner fender you will see the starter relay. With key switch ON use a wrench or similar to jump the two large terminals on the relay and the truck should start (make sure the trans is in neutral).

 

The clutch safety switch snaps on to the clutch master cylinder
push rod. It's black in color, cylindrical in shape with an electrical
connector plugged into it. If you unplug the connector you short
the two Red/Light Blue wires together to bypass it.

Here's a picture of the clutch safety switch.

 

Thank you for the diagram. I was able to locate the switch and to jump the Red/LtBlue wires which resulted in proper operation of the start circuit with the key. Here is where it gets confusing...since jumping the switch worked, indicating a failed switch one would think replacing it (which I did) would solve the problem. Nope, new switch, same problem (engine won't crank with the key).

I notice that the clutch linkage under the dash is pretty sloppy; the whole mechanism seems to "flex" when you step on the pedal and the big return spring does not return the pedal all the way to the top of its travel. Is it common to have likage issues? Could this be affecting the operation of the clutch safety switch?

Thanks.

 

The plastic bushings on the right side of the clutch pedal shaft wear out. Mine was bad enough that it started wearing into the steel bracket, so I had to do a little welding and grinding to get the play out.

 

There are two common problems with the clutch linkage.

1) As mentioned above, the plastic bushings wear out where the clutch
pedal pivots. If you do an advanced search you'll find many threads about
the problem. There was also a recent post about the pedal bracket assembly
cracking.

2) The usual problem why the clutch safety switch doesn't work is because
as you press down on the clutch pedal the round plate under the hood the clutch
master cylinder bolts to pulls away from the firewall. The plate was glued
to the firewall. Eventually many cracks develop around the mounting plate.

To manually operate the clutch safety switch. Reach down
and pull it towards you. If you can start the vehicle you have the flex problem.

Here's a link which contains another link that describes the fix in detail.

https://www.ford-trucks.com/forums/1...ml#post9903956

 

Great information! Thank you.

 

Those Ford steering columns are well known for having key and start problems, that stem from the column. Lots of people put a push button start switch somewhere around the column area. I had to do that, as well.

 

It already had a push-button starter but that was due to the Upper Ignition Rod being broken. We got that all apart and repaired already. Let me tell you that was an adventure!

But I know it isn't anything in the column because when I jump the clutch safety swith, the key works fine.