Does anyone know how much current a typical thermocouple pulls?

I recently installed an Isspro 3607 pyro that required two hot wires, one for the gauge lights and one for the thermocouple/control box.

I wired the hot wire for the gauge lights into the headlight switch so that the gauge lights come on when the head lights are turned on and can be dimmed with the gauge cluster dimmer switch. Hopefully the pyro gauge lights won't pull so much extra juice that the headlight switch gets cooked. I put an in-line 3A fuse in-between the gauge and the tap into the head light switch wiring, to prevent a short in the gauge wiring from burning up my headlight switch.

And I ran the hot wire for the thermocouple to the auxilary post on the back side of the fuse box under the hood. I put an in-line 10A fuse in this line, to prevent burning up one of the big aux fuses if this line should ever short out. The problem with this power source is that it's full time power, so the pryo is still displaying readings from the thermocouple even when the truck is off. And, embarassingly enough, I can't figure out how to use my DMM to measure the current.

I just don't want to come outside some morning to a dead battery.

Do you mean how much current is the display pulling? If so, all you have to do to measure current with a dmm is basically put the leads in series with the hot wire and set the dmm for current. I would be surprised if you see any more than 10 or 20 milli amps. Don't worry about it :exactly:

In series? So I just need to disconnect the pyro lead from the power source, put one of my DMM probes on the end of the lead and the other end on the power source?

Like I mentioned earlier, the pyro kit requires two power supplies. One for the gauge lights, and one for power to the control box. I'm guess the control box supplies power to both the gauge (for gauge operation) and the thermocouple. But you're thinking that would only amount to 10 or 20 mA?

ya. the thermocouple itself really only produces a reading by changing voltage at the tip, kind of like a battery that changes voltage with temperature. the display is only a type of voltmeter that SEES the voltage change as a temperature change. see what i mean? the other wires that provide you display and lighting power are the only ones that will draw any current and that should be very small overall. where it gets confusing is the word "thermocouple" usually just refers to the wire itself and the pyro is called a didgtal thermometer. not trying to be anal just trying to keep us both from getting confused. the voltage from the thermocouple wire is only -.611 mv @ 0 degree f for type j thermocouple wire and 29.521 mv for 1000 degrees f. for type k it's -.478 mv for 0 degrees f and 22.255 mv for 1000 degrees f. these are the two most common types of thermocouple wires used for pyrometers. so you can see it takes very little voltage change to read a large temperature change on the display.

Why not connect the +12v supply wire to switched IGN - a terminal just for that eventuality is available in the Convenience Center, fused and unfused, iirc.............

That cktry draws over an amp at certain temperature ranges, also iirc.

I ran some functional linearity tests on the various ISSPRO electronic module gages, when I installed mine, with more than interesting results.

It's been three or four years, so don't quote me, but I would definitely run the module power to switched IGN

Why not connect the +12v supply wire to switched IGN - a terminal just for that eventuality is available in the Convenience Center, fused and unfused, iirc.............

So where exactly should I connect the pyro hot wire to an IGN circuit? On one of the fuse panels (which fuse do you recommend? using an add-a-circuit?)? Tee it into a wire someplace?

If the pyro pulls over an amp at certain temps, I don't want to overload any circuit and start blowing fuses or cooking switches.

Use a relay, the light switch can trip the relay and you can pull power from the 12v constant in the ignition wiring harness to supply the juice to the gauge. Any time you want to use a low current switch to control a higher current item you can drop in a relay for a couple bucks, standard auto relays will handle 30 amps.

Should be a Convenience Center under the driver's-side inst panel, with a number of spade-type connectors available for lighting, accessories, etc - a set should be labeled SW IGN, or equiv

Should be a Convenience Center under the driver's-side inst panel, with a number of spade-type connectors available for lighting, accessories, etc - a set should be labeled SW IGN, or equiv

Do you mean under the dash, left of the pedals, on the firewall?

Not sure of exact location, but the panel is for connection of various in-cab accessories and such to respective power sources.

Sorry man, I'm just not finding it.

Anybody else have a clue where this convenience center might be hiding?

i used the brown wire(illum) from electric brake harness to power pyro and lights, have to turn on lights to get power unless dark outside then dont need to mess with turning it on. mines an 02 so yours might be different. hope this helps

Look where your left foot goes, Wade. On the firewall, there's a place where wires come through from the fusebox under the hood into the cab.