TR2/3/3A heater rheostat wiring TR3A

[NutmegCT]

I ran water through my heater, and verified it circulates. Warmed up the engine, and sure enough the heater gets hot.

Turned the heater switch and the fan didn't come on. There's no power going to any of the *three* wires on the rheostat. Here's the current setup:

A black wire from rheostat terminal 1 to a cigarette lighter (terminal on the back of the lighter).

Another black wire from the rheostat terminal 2 to the heater motor.

And yet another black wire, also from rheostat terminal 2, into the harness under the dash.

Advance wiring diagram shows a green wire from fuse box A2 to rheostat, and a black wire from other terminal of rheostat to motor.

My fuse box has no A2, just an A and an A1.

Does my current wiring sound at all correct to anyone? Should I disconnect all those black wires and match the Advance diagram (using A or A1 instead of the missing A2)?

Thanks.
Tom

 

[martx-5]

All the fuse boxes in the TR2's thru TR3B's had two fuses. That makes four connections. Call them whatever you want. Whatever they're called is immaterial. One fuse is hot all the time, and the other is hot with the ignition on. The rheostat only uses two wires. One comes from a 12V source...Dan Masters shows it should go to the side that's hot all the time. I don't know if that's correct. Either way, there just needs to be a wire coming from the "green" side (either brown and green, or just green) of one of the fuses to the rheostat, and then to the blower motor. Also, the blower motor needs a proper ground.

 

[Geo Hahn]

The cigarette lighter is of course an add-on.

On my 3A terminal A2 is at the upper left corner of the fuseblock (terminals are labelled) the fused side of the horn circuit.

I believe a green wire circuit would also work and may be easier to find behind the dash. One benefit of a green wire circuit is that the motor will shut off when the ignition is off (not that you're likely to forget it's on if it is as noisy as mine).

 

[MGTF1250Dave]

Aloha Tom,

Your wiring sounds as if the intention was for the 12V power to be supplied from the cigarette lighter to the rheostat, to the motor and then to ground (the black wire in the harness. Perhaps someone earlier moved the black wire in the harness from the heater motor to the rheostat terminal # 2. I am working on the assumption that the black wire in the harness is a ground.

Does the cigarette lighter work? If so, move the ground wire to from the rheostat to the heater motor ground terminal and see what happens.

You can test the heater motor with a couple of jumper wires, one lead from a 12V source like the A4 (green wire side) terminal of the fuse block to the motor and the other from the motor to a good ground connection.

Radio Shack has a package of various colored wires with alligator clips that are handy for electrical testing. Here an example:

https://www.radioshack.com/product/index....rentPage=family

Once you get everything sorted out, I would recommend you use Art's and Geo's wiring suggestions and provide a separate wire from the A4 terminal to power the rheostat. The cigarette lighter and the heater motor both on together would draw allot of current and may overload the wiring.

 

[Don Elliott]

Tom - Whenever I want to solve an electrical problem on my TR3A, I get out my 10-foot long red and black jumper wires with the alligator clips on the ends and connect these to the item in question (like the 2 wires going to the heater fan) and the far ends to the battery post and to the ground - like the stud on top of the valve cover. If the item (heater fan) works, I look a bit further back (like towards the rheostat) till I sort it all out.

 

[TR3driver]

I believe the original connection point for the heater rheostat was the 'green' terminal on the fuel gauge. But it's logically equivalent to the A2 on the fuse block, so you can use either one.

I wouldn't keep the cigarette lighter powered from there, though, as an actual cigarette lighter can draw a lot of current, and the original ignition switch isn't really designed for it. IMO the lighter should stay powered all the time anyway (although a fuse is certainly a good idea).

 

[NutmegCT]

As always, I greatly appreciate these suggestions. I've decided to follow the wiring diagram, find a green wire behind the dash (probably from the fuel gauge?) and add a green-wire branch to the rheostat. Sure wish I knew where that second black wire runs in the harness.

What gauge wire should I use? There's a lot of current drawn by that heater motor - I don't want a melt-down!

Thanks.
Tom

 

[Don Elliott]

My heater wires are the same size as all the others. It's only a little fan motor.

 

[angelfj1]

Don: You might want to consider putting a fuse or resettable circuit breaker in series with your test leads. A dead short on a fresh battery can easily melt those wires quickly and burn your hand or cause a fire. /bcforum/images/%%GRAEMLIN_URL%%/nonono.gif

 

[TR3driver]

My heater wires are the same size as all the others. It's only a little fan motor.

/bcforum/images/%%GRAEMLIN_URL%%/iagree.gif If yours is drawing more than 4-5 amps, the bearings in the motor are probably bad and binding. Good way to burn up the rheostat.

18AWG is plenty, although I would probably go for 16 just because I like overkill when it comes to wires.

 

[NutmegCT]

It's working!

I removed the "extra" black wires, ran a new green 14AWG wire from ignition switch green to the rheostat, and cranked 'er up.

Nice gerbil-strength airflow. I'll eventually be getting the front and back rubber seals for my hardtop, so I can test warming up my toes this fall.

Also, decided to leave that cigarette lighter receptacle connected, for use as an accessory plug: a small 12v tire inflator, cell phone charger, CD player (for pre-1970 music of course ...).

Thanks again all.
Tom