Truck is an 88 F250 302, zf transmission, 4x4

The wiring was screwed up, so during the rebuild I used the wiring from a 1991 F150 302, E40D. Now I would like to be able to get rid of the MLPS. Hook up the reverse lights and 4x4 hi/lo dash lights etc.

Currently I require the MLPS even though I have removed the plug from the clutch interlock switch wiring and have installed it to the actual switch, The clutch interlock switch works as it is supposed to only if I have the MLPS still connected.

Initially I used the ecm from the 91, however it not only set codes but also ran like crap, hunting idles, stalls etc. So I replaced it with the bronco ecm that was in the 88 prior to the rebuild. The bronco ecm is a replacement, the original ecm was fried by an inept mechanic, I was told that this ecm was for a manual transmission.

So is there a way to jumper the signal from the MLPS? I am reluctant to just try it because it appears to be a potentiometer and in park is not a fully open circuit...

tia.

 

If it's like my 95 there are 4 wires you need from the MPLS plug. Two that are connected together when the MPLS is in park or neutral which also go to the neutral safety switch. Then there are two for the backup lights. When I did mine I just used a multimeter one the MPLS and cycled the positions to find the correct ones.

 

If you have a manual truck PCM, you should be able to grab a manual truck trans wiring harness and be good to go. Not sure I'd do it any other way on the older trucks.

The manual truck harness should have a plug on it for a manual shift Tcase 4x4 indicator light and a plug for reverse light switch on the ZF5. The clutch pedal position sensor plugs into an under dash plug that is on all trucks (manual or auto--the auto trucks have a jumper in place of the switch, then use the MLPS as neutral safety instead, whereas the manual trucks trans wiring harness has a jumper in place of the same neutral safety circuit and the clutch pedal position switch operates the circuit).

If you're using an auto PCM, just leave the MLPS in neutral, plugged in, and zip tied to the frame rail. I have a thread a few days old going about doing this for a 96' F150 (not as straightforward), and I posted links to a bunch of helpful info. From what I understand the truck won't run perfect with an auto PCM and a manual trans (pushing in the clutch to shift can cause a brief surge?), but shouldn't be too far off. Many guys run them like this. The reverse lights are going to be the tricky part, but if you check all the links I posted (I think it was one of the later ones), one of the them discussed what the MLPS wires do, so you could (maybe) grab the reverse light indicator wires and wire it up with the trans switch.

I'm sure someone that has actually done this instead of just reading about it will chime in soon.

 

I am not sure about this though, I also cycled through the mlps. There was only one position that had full continuity, the switch was in what I believe to be the neutral position. The wires were a red/white going to the white plug on the main harness the other was a blue, that turned to black it was tied into the speed sensor.

Another pair of wires a green/red and blue/yellow read 0.08 ohms in what I think was park and increased through the range of shifts until it read 4.17 in what I would think was 1st.

 

I believe the ECU is for a manual, and I suspect you are correct that would be the best way to resolve the problem. Although my truck was always a manual, it was not a 4x4. The transfer case and the transmission are not the originals, I don't have that particular portion of the wiring. I have called around the wreckers and haven't had any luck in finding the wiring yet though, so this was why I wanted to see if I could just make it up myself.


Now thats the jumper that I need ... The clutch interlock jumper I already removed and hooked up the wiring to the switch.

With the auto ECU the motor ran like crap, all the wiring, sensors, emissions came from the 91 (auto) so it wasn't due to some other incompatibilty. Once I hooked up the 'manual' ECU the engine ran good.

Thanks for the suggestion re. your previous thread, one of those linked I hadn't read, it had pictures of the transmission wiring....

 

Reverse lights now working I spliced into the connector to the MLPS... I retested it for continuity in different positions and found 3 positions that were open circuits, park, neutral and reverse. Jumpering the park and neutral had no effect as I suspected. Found this diagram that explains how the MLPS works (kinda), it did confirm what I thought though.

http://oldfuelinjection.packrad.net/..._1995_30-1.gif