Thanks!

 

Another Question on the Overdrive solenoid for you electrical types....An25 in the service manual (at least for 90).

So the overdrive lockout solenoid gets its ground from pin 55 of the old SBEC. Pretty sure this ground is controlled by the SBEC in two instances. Two are of course throttle position and RPM, which I'm replacing with a vacuum switch and pressure switch from PATC. That part's easy. I also want to retain the function of the overdrive switch in the dash, and from deduction and the picture of the dash control module it looks like the switch turns on the transistor which allows current flow all the way back to the ground in the dash (H4 ground splice). That's accomplished through pin 44 of the SBEC and pin 44 of the bulkhead connector. So, I'm thinking I can simply tie wire 44 to wire 55 (which would allow the dash button to work - disable overdrive), and in series, the pressure switch from PATC for the pressure point to actually switch into overdrive.

Sound about right?

 

*ponders* I don't know if the factory button is ON or OFF to disable OD; if ON, then no, it won't work (or rather, will work backwards).

It might also be a pulse to trigger the ECU to handling it.

What you can do is add a SPST switch between the vacuum switch and the pressure switch; open, no OD - closed, OD.

Worst case is to set a latching relay up to toggle that wire for you. But, then again, if the circuit OPENS and stays open to turn OD off, you should be able to do what you're looking to do; I just don't know offhand which way it is.

(No, that's not covered that I've found in the FSM ... which doesn't mean it isn't, but is a nice way of saying "Hadn't been arsed to look since my 3 speed doesn't HAVE an OD switch!" *grins* )

RwP

 

Well I've never had a running truck so maybe you know.....the way the FSM shows the setup the led indicator and the transistor to ground are the same state...when the button is pushed....so does the led light up when the button is pushed and is this overdrive enabled or disabled? I doubt it's a signal to the ecu....there'd be no reason to provide a transistor switching to ground. Pretty sure it's switching to ground to provide a path to ground for the solenoid which is higher current than the ecu would handle. But then again, Lockup solenoid comes from the ecu too, so I don't know.

yeah I'd thought about sticking a relay in there on the switch...then I could just pick the state I need to interrupt the pressure switch.

Speaking of the lockup solenoid, what the heck is the "Fuel Pacer Lamp (Manual Transmission Only)". The lockup solenoid ground goes to this lamp on the dash (connection H), but what would that be? Especially since mine is an automatic. In some reading it indicates it might be a fuel saver lamp. But I thought the lockup solenoid came on at higher speeds, lower throttle (cruising)? IE, the ground is applied to the lockup solenoid under this condition. But that would also illuminate this lamp. This seems opposite, as I thought the lamp would come on when you're gunning it. It's also odd that the FSM calls it the UNLOCK solenoid, as if energizing it unlocks the converter. But all I've read, says energizing the solenoid locks the converter.

 

Heh. The ECU lights up the Fuel Pacer Lamp to signify "You're revving too high for fuel economy, boy, better shift outta Granny!" *grins*

RwP

 

That's what's confusing....If you look at the FSM AN25, that light is piggybacked onto the lockup solenoid ground...It's the OR/BK wire #54 from the SBEC, #20 on the bulkhead. Which means the light would come ON when the lockup solenoid is engaged. Having taken the harness apart, I can confirm the two OR/BK wires on Pin #20...one from the SBEC, one to the solenoid. Having the light come ON when the lockup is engaged which would be low throttle about 50 MPH, is opposite of what I would expect. However, I've also learned that Dodge most times left the lamp out in Auto's. It was an "option". And the FSM says it's on manual transmissions only.

 

*ponders* That might explain why mine lights up sometimes (albeit dimly!) since I LED'ed the whole cluster.

I never traced it that far, since mine wasn't manual.

(I lamped it because, on some cars *like the Thunderbird SC* it can be used for diagnosing no-start problems by how the ECU treats it.)

RwP

 

So, where is the Transmission Temperature Sender and Lamp? I have a plug in the harness for the sender....It's shown on AN19 of the FSM. The note says "In Cooler Line by Radiator, 3.9L TBI only" but I had no fitting for it, and I can't find the sender on Rock Auto. It also shows going into the cab through bulkhead connector pin 11, which illuminates a separate lamp (not part of gauge cluster) and the note says "On steering Column Cover". Can anyone with an 87-90 3.9L, confirm this sensor/lamp combo exists? My connector is all broken and I'm wondering if it was ever used or one of those factory add-ons that never made it to production. I cannot find the sensor mentioned in the harness diagrams, nor can I find the lamp mentioned in the interior console diagrams, except on page 8W-13 where it shows a steering column connector.

 

It doesn't exist on my 1988.

RwP