My computer is drawing on the batteries when the ignition is off and is killing them overnight. When the computer is unplugged the drain stops. I would like to put a toggle switch on the power wire for the computer. Has anyone else had this problem?

 

Usually the IOD (ignition off draw) problem is caused by a CTM (central timer module) failure but I'm not sure if your '98.5 even had a CTM.
If it does it has seat belts that lock after you start driving.
CTM failure causes belts to stay unlocked when the truck is parked.
Unlocked mode uses power.
When the CTM is operating normally they lock when you get out of the truck and unlock when you open the door.

Another thing you can do is hook up a meter in ampere position as shown below and start pulling fuses one at a time to isolate the problem.

 

That is what I did and found that it was the computer. I am just unplugging the computer not when the truck is parked until I figure out which wire to put the switch on.

 

I would guess that it is something the PCM controls, but not likely to be the PCM itself that is at fault. As Infidel mentions, the seatbelt module on a quad cab is a high power consumer if it sticks on. Park your truck, shut it off and walk away with the windows completely open. Come back in 40 minutes, reach in the window without opening a door, and see if the seat belt retractors are locked, or if the belts will still pull out. If they are not locked, you need to diagnose the seatbelt module.

Any fault can be diagnosed and a repair can be made, instead of sticking a switch in a random wire.

 

I will give it a shot tomorrow. Thanks.

 

Seatbelts were locked.

 

I'm not falimiar with TST PM3 but is it possible its powered off of wrong circuit?

 

No. I have had that installed for a few years. Nothing has been done to the truck lately. The power drain started for no apparent reason a bit ago.

 

Did you figure it out? I've been dealing with same problem and finally found the glove box light to be a major problem. I just unplugged it from the harness--don't really need it.

 

Unfortunately not. I work out of country and have been away for three weeks. I will do a little more poking and prodding when I get back. The light fix you up then?

 

Glove box light switch was a problem, but it was not the problem. Disconnecting that got me from 10.5 milliamps to 7.5 milliamps. My seat belts were also locked when I checked them, but I decided to check out the sctm anyways. When I got that unit disconnected, I'm getting .3 milliamps. I'm pretty sure this is in range we're looking for. Now I need to locate the replacement part somewhere.

 

56043003AD is the part number for sctm. Just ordered mine from dodgetruckparts.net for $22. Way cheaper than anywhere else I could find.

 

I am curious to find out if this solves the problem. I am not back home until mid week to check mine again.

 

I ended up doing a mod somebody talked about in an old post. On sctm wire harness, cut pink wire and splice from blue wire. Problem solved (for now). Power on pink wire is constant and timer is supposed to shut it off. Power on blue wire is switched. Have to key on to release seat belts now. Multimeter now shows .3 milliamp key off draw, instead of 7.5 ma key off draw.

I will post results when I get the new sctm and restore the wiring. Let me know what you find out when you get back.

 

I just did the mod today and it has brought the draw down. I will order the new module. Thanks for the tip.