my 93 grid heaters quit working. when you turn the key on i have no wait to start light no check engine. if you turn past on to start the W.T.S light and water in fuel light comes on if you let it sit with the key on. sometimes the relay on the drivers side fender will start to click rapidly and then turn on the grid heaters.if you just start the truck the wait to start light flashes all the time.
I have checked all the the grounds and cleaned them. tested all the fusible links.have power on one side of the small wires on both heater solenoids. power to one big wire on top of both solenoids. Thanks in advance

 

Had the same thing happen on my 93 a few years ago, the PCM that sits behind the battery went bad. Started with the relay clicking rapidly when cold and got worse until it stopped working.

 

so is the PCM the computer

 

Correct.

 

I see your truck is about identical to mine. I think the computer runs the AC, charging sys, cruise, grid heaters, and maby the speedo. Everything is pretty easy to wire to manual except the speedo. I just dont know about the speedo.

 

I found that wire the PCM grounds to operate the grid heater and rigged it on a toggle switch to ground and it works! external volt reg is taking care of charging duties.My a/c dont work and no cruise.I modified my gauge cluster and run and older cable drivin speedo head in the cluster its within 2-3 MPH and most important to me is I have a working Odometer...FWIW the gauge cluster looks OE you cant tell Ive screwed with it

 

you should change your toggle switch to a momentary push button just in case you bump it and it stays on. Nothin worse then coming out to a dead battery from the grid heaters staying on

 

Good idea because it could be even worse when stuck on and the wiring catches fire = no more truck!!

 

was this one of the wires coming off of the solenoids? Crafty solution to the speedo!

 

Checked the PCM from the info in the sticky. The PCM is bad I will order a replacement. Thank you all for the info. I'll let you know how it turns out.

 

Its about 50 degrees outside and moved my truck and everything works again. The grid heaters work and I have AC and cruise. The battery is charging now and everything seems to work. We cant figure out why it would work in the warmer weather. Have any ideas of what it could be?

 

50° is about the high limit. A few degrees warmer and it won't cycle.

Also, it's the manifold temp that's being read, so if it is warming up outside, the temp that's being sensed might be lower.