Engine/Transmission (1994 - 1998) Grid heater relays ...

[MHalloran]

I purchased the heater relays from Genos. My truck is a 96. Relays in place are still original. Heater doesn't cycle the volt meter like it used to. Connections are clean. Relays I got sent to me (#75565)are larger but are supposed to be for this truck they say. Got 2 of them because there's 2 there. Need to replace both right? There's 2 sets of terminals on each one. Both larger than stock ones. Can anyone tell me which set I use? Does it matter? Can wires be flipped & still work? I appreciate any input. Thanks.......Mike

 

[GAmes]

At the risk of misinterpreting your question. As long as you are in there might as well replace both. The large wires carry the full current load from the battery to the grids. They can be positioned on either of the large posts just like a switch. Same goes for the small terminals. One is a constant hot, the other is a ground that is controlled by the PCM. When the intake temp sensor sends a signal to the PCM that the air is cold the PCM activates one or both of the relays, dependent on how cold it is and vehicle speed. The length of time they are activated is also dependent on how cold it is. The wait to start light on your dash is lit as long as the PCM determines the grids need to be on. It IS NOT an indicator the the grids are actually receiving power or that the PCM is supplying ground however. I bypassed the PCM and have the grounds hooked to a toggle switch. I think the grids coming on after the engine has started is annoying, especially when pulling out of the driveway while the headlights are going from bright to dim. My wait to start light still illuminates for varying periods of time. Some times I flip the toggle off when the light goes out, sometimes I never turn the grids on. If it is really cold, 20 or below, I'll cycle the switch after starting the engine if it is stumbling.

You can learn the theory of operation about the grids and nearly every other system by opening your factory service manual. If you don't have one, Genos does.

 

[MHalloran]

Brother your reply here is a huge help. So even these small wires can be flipped on each relay? Doesn't matter which post they go back on? I'll just have to clip off old 90 degree connector cuz I don't think they'll slide onto new posts. Too small. New nuts came with new relays anyway.Ill crimp on new connectors. GAmes you've been on this site helping us out for years. I recognized your name. (Is it Greg?). Thanks my friend. Do I need to know anything else? I so appreciate your help.........Mike

 

[GAmes]

It is Gary. I was slightly in error, the small terminal's power wires are not constant hot, they are switched hot (fuse #9, the same one that activates the FSS relay). I know of no reason why they would be polarity different. My after market relays seem to work OK but are oppositely wired. Thanks for the flowers.