Constant 12V for Transmission Temperature Gauge

[dherman304]

Im trying to install a Transmission temperature gauge before some longer trips I have planned. I can't decide what to do about the 12V constant power wire the gauge requires.

1: Why does a temp gauge or any guage need a constant power wire?
2: Can the constant 12V wire be tied into the 12V ignition trigger (I have a stepdown triggered on an ignition relay for other 12V accessories)
3: Can I tie the 12V constant wire into one of the two batteries? (I dont want to do this, I want to keep both batteries as close to the same charge as possible.

I know this is kind of a weird general question but Im just looking for a second opinion.

 

[dherman304]

I talked to the Gauge mfr and they said its perfectly fine to tie they constant source into the ignition sourced power. Mechanic brother in law said the constant power may be used to store programs or functions (like high/low or what color to display) since Im not too concerned about that Im goign to tie it into the ignition source wire.

 

[Retiredwarhorses]

I talked to the Gauge mfr and they said its perfectly fine to tie they constant source into the ignition sourced power. Mechanic brother in law said the constant power may be used to store programs or functions (like high/low or what color to display) since Im not too concerned about that Im goign to tie it into the ignition source wire.

thats great, except your truck is 24v….you can wire a relay to be activacted upon turning The 24v ignition with 12v on the other side, or if you have 4 speed truck you can tap off the 12v feed to the TCM at the transmission relay.

 

[dherman304]

thats great, except your truck is 24v….you can wire a relay to be activacted upon turning The 24v ignition with 12v on the other side, or if you have 4 speed truck you can tap off the 12v feed to the TCM at the transmission relay.

well aware its 24v hence the problem.

"2: Can the constant 12V wire be tied into the 12V ignition trigger (I have a stepdown triggered on an ignition relay for other 12V accessories)" - from my first post.

 

[Retiredwarhorses]

well aware its 24v hence the problem.

"2: Can the constant 12V wire be tied into the 12V ignition trigger (I have a stepdown triggered on an ignition relay for other 12V accessories)" - from my first post.

you don’t want anything that is contant power…just keyed, unless the draw is so small as to not drain the battery.
You can just pull directly from the rear battery…but that could and can degrade the rear battery.
Not sure why you need this temp gauge, but its You’re truck.
The TOT is readable on the correct diagnostic equipment because the thermal temp probe is part of the transmission internal harness.

 

[Mogman]

When you say "12V ignition trigger" do you mean switched 12V power?
Most likely it would work on switched power unless it has some programmable perimeters, in that case you would likely lose the programming.
Your R1 should have a dual voltage 200A alt so you could connect the 14V stud from the reg to the 12V connection between the batteries and then pull a limited amount of power from the 12V connection and the reg will balance the batteries.
Post a link to the gauge.