Hello, I'm currently attempting to figure out why my grid heaters aren't working. Two of the large posts on the relays are getting constant 12v power (Good fusible links) i notice when i turn the key i hear no clunk. I went ahead and tested the four small posts with the wires connected. With the key off, i took readings of 0.1V for each one, the orange/black striped, the blue, the yellow/black stripe, and the other blue all reading 0.1V.
With the key on I tested all of the posts again, two of the large posts have 12V the other two large posts have 0V. Upon taking readings of the four small posts with the orange/black stripe, the blue, the yellow/black stripe and the other blue I came to find out that EVERY SINGLE ONE has 12V power with the key on.
So, is this how it is supposed to be? help!!!!!!

 

You have a ground problem. Follow the black striped wires to where they are bolted to fender.

 

thanks, i will report back in a few.

 

The yellow/black and orange/black both run into the wiring loom and go into the ECM behind the battery.

 

I disconnected the battery, i disconnected and removed the ecm plug from the ecm. I reconnected the battery and i found the yellow/black stripe going into CAV # 5 (Signal ground) while the Orange/black stripe goes into CAV #6 (5 Volt supply). Both CAV #5 and CAV #6 have 12v at the plug with the key on, obviously the other end of the respected yellow/black stripe wire and orange/black stripe wire are connected to the grid heater solenoid on the small posts. so that is where they are getting 12v from then?

 

bump

 

not sure what the point of checking that was but would be happy to hear why

 

Also, with the ecm disconnected and the battery connected i turned the key to the "on" position. i pulled all the small wires off the solenoid posts to test them individually, both the blue have constant 12v with the key on, the yellow/black stripe has 0V and the orange/black stripe has 0.10V constant. when you connect them to the solenoid posts with the key on, they all read 12v.

 

no one on here has a clue? sick

 

If anyone is reading this, I've got an update for you all on my 1993 W350. The ECM is getting power from CAV #18 on the plug from a red wire that was connected to 12v when i did the fusible link delete. Every time i touch my grounds to the battery it blows that fuse that feeds that red wire, so obviously it has a short somewhere in the system. i checked all of about 2 feet of that red wire and it looks fine to me. I removed the ECM once again and replaced the fuse and i connected the negative side of the battery with no spark at all and no blown fuse. Also, FYI I'm using a 20-amp ATC to feed that specific power wire, since its ~14G. So, now what I'm trying to figure out is would this be an internal short to the ECM, or could it be any number of the systems the ECM feeds with a short somewhere within. hmm.. it seems I'm nearing a resolution. Does anybody know anything about this CAV #18? The PCM wiring diagram is blank on my end for that CAV#

 

This is the schematic from the service manual. You should get the service manual. Notice the grounds are the black striped wires. If you have 12v at all wires like you say, you are not getting ground. Dodge is known for ground problems.
heater

 

dguru, I believe the wire diagram you posted is for the earlier non intercooled models so will be no help for Triggerfish as he has a 93, do you have the diagram for the later models?

 

Triggerfish, another thing you can do is look in the stickies in the top of the page under the "electrical" section might be something there that will help.

 

see if this link works. Its a system diagram that might sort things out

https://charm.li/Dodge%20and%20Ram/1993/W%20250%20Pickup%20L6-359%205.9L%20DSL/Repair%20and%20Diagnosis/Powertrain%20Management/Diagrams/Electrical%20Diagrams/System%20Schematics

there is another page that shows pin location. 18 is not used. You could be powering a ground that is used in a different application

 

Looks like the 93 has a PCM like the 94 so here is a 94 diagram. It shows that the relays have ignition power and that the PCM switches the ground signal of the relay. With that said the PCM may be the problem. Are all other PCM functions working like tach, alternator, trans OD, etc? If other functions are working it looks like PCM problem and they are hard to find now. If thats the case you could add a simple push button switch on the PCM wires from relays and manually use heaters as needed. Or you could make a timer circuit to automatically do it.