Hi there my truck is a 1990 dodge w250 diesel and it will not start when temps are colder around -10c, 14f. When I turn the key on the wait to start light comes on for about 10 seconds or so than it makes a slight click sound, solenoid closing. It use to make a loud clunk sound and fire right up. My first though was the solenoid wasn't working property so I hook up jumper cables from the positive post on the battery to the two studs on the grid heater. The truck still won't start so now I am thinking the grid heater is burnt out. Is there a way to test the grid heater? am I doing something wrong? I check the battery it was 12.34 turn the key on the fan was on high so I shut it off and the voltage droped to 11 something. I check it again and the voltage didn't drop.

 

When the wait to start light is on, there should be battery voltage across each pair of grid heater connectors. (2 pairs)

With the key off you can measure the resistance across each pair. It should be nearly a dead short. (0.1 ohm)

 

Check the ground wire at the grid heater. Mine rotted completely off and it was causing my heaters to not function, or intermittently as well.

Add an additional ground from the engine block to frame to battery negative post. Our grounds are a problem with these trucks, as it's been mentioned many times. By doing this , you can eliminate a lot of issues like this, although it might not just be a ground issue for your problem. At least it's a good start to limiting what it might be.

 

Ground wire is good, I add a temporally extra ground to the frame and the battery post and still no voltage drop on the battery when I turn the key. I undid the two wires going to the grid heater and used jumper cables, this time one negative and one positive to the battery. I check the voltage and it was down from 12.74 to 11 something and the truck fired up. I am thinking it must be the grid heater relays/solenoids or its the wiring.

 

On each grid heater relay (coil terminals) there's a blue wire that should be at battery voltage. The other (orange or yellow) wire is driven to ground by the PCM when the grid heaters should be on. If those two conditions are met, then the relays are bad. I'm assuming you've verified 12V to the power side of each relay.

If the PCM doesn't drive the relays, odds are pretty good the problem is the air temp switch (intake manifold) or it's wiring.

 

There is no blue wire for the coil terminals there is a black wire, orange with black strip. Yellow wire with a black strip and a black wire. I understand the the wires with a strip are the ground wires and the black ones are the positive wires. I check the voltage and its around .30 v on both terminals with the key on and off. I than ground the two ground wires and ran the other two black wires to the battery positive. It clicks like it does when the key is turn on but I get no voltage drop. I seen a link on here for cleaning the solenoids I am going to try that, if that doesn't work I going to buy new solenoids/relays I have to look for that post about the white rogers relays as my dealer would want lots of $$ for them.

 

I might be wrong on the power wire. Doesn't 1990 have a dedicated grid heater module?

Here's the relay information.

 

Not sure about the grid heater module. I check the resistance in the two wires from the postive battery to the relay and one wire had resistance and the other did not. I check the fusible links on both wires and there fine. I also jumper the wire that had no resistance to the battery and there was still no voltage drop. Even with both power wires removed from the relay, the relay still made the same click sound when I turn the key on.

 

A click indicates the relay is being driven. If power is available on the contact side, the heaters should run.

Crimped connectors can fail inside the crimp, or in the wire a short ways from the terminal.

Should be a simple case of ******* the power flow.

 

Took the relays a part, the contacts look almost brand new, no corrosion I tested them and the click. I installed four new wires for the grid heater and the darn thing still doesn't work. Works if I hook the wires directly to the battery and bypass the relays. Any other ideas? I might be wiring with a push button like other have done.

 

Hey there. Newbie here with a 1993 w250, and i have been reading the forums alot, trying to find the issue with mine. When i turn my truck on, the "wait to start" comes on, but the ECU doesn't seem to be sending the signal to the relay. It has 12V to both, and the ground is good on the heater itself. When i take a ground wire from my battery to the orange or yellow wire, the relay clicks and the heater starts to do its thing. So, do I have a ECM issue?

 

Old thread you brought up. At what ambient temp. is it when you try to start it?

 

Yup. An old thread for an old truck. It's -10 degrees Celsius at least. Cold enough