The Stovebolt Site Forums The Shop Area The Electrical Bay Heater fuse requirements

I purchased a “Heater & Defrost Assembly” part # 68-991 (12 volt) from Classic Parts. It is going in my ’53 3600. The instructions say “Wire the heater, as shown in wiring diagram to a fused vehicle circuit”. The circuit is a simple sketch with a line from the ignition switch to the heater switch, then to the heater and then ground. No fuse size is given.
There is a warning in the instructions “Caution: Switch not intended for dash mount. Coils may get hot. Isolate least 5” from wiring and flammable materials”. It sounds like it will draw heat like a soldering iron.
Should I assume that the ignition switch is fused and any wire exiting the ignition switch would work or should I put an inline fuse between the ignition switch and the heater switch and if so what size. Classic Parts says they can’t answer this question. Any advice appreciated.
John

no the ign sw is not fused, get an inline fuse to put in the hot wire or if you have a fuse panel with an unused slot, get power from there [best alternative] ... size usually 9-10amp, might indicate current draw on the motor, should say in the sales listing ... the multi-speed switches do get hot, but are mounted to the dash originally, there are no flammable materials under there except wiring, which of course you will keep clear of

I'd say if Classic Parts can't give you that advice, they shouldn't be selling the product - or you shouldn't be buying from them!

Bill

You will need a 20-30 amp fuse.

I would go with the 10 amp fuse. I can't see any way you would need a 20 to 30 amp fuse on there and the wiring to the ignition switch could not take it.

I have easy access to two wires. My fuse block is full. One of the wires is 30 amp and feeds the headlights. Of course, it is not controlled by the ignition switch. I have already added a wiper motor to that wire. It is heavy gauge but don't know how big.
The other wire is labeled on the fuse block as "Radio" and is controlled by the ignition switch. It is 10 amp and has a smaller wire. I do not plan on adding a radio.
I assume that the reason that the meager instructions said to connect to ignition switch is to keep the fan from running when you turn off the ignition and exit the truck. I can't think of any other reason.
John

I believe the in-line fuse to my heater/defroster is 8 amp. I'd think a 20 amp would allow your motor to sustain damage if a short occurred. I don't think the windings in the motor would handle that much current.

use the radio point on the fuse block, do NOT use the headlight circuit or you may find yourself without heat AND lights some cold night ... the fuse block generally is powered from the ign sw so all accessories go off with the key

Bill

I will use the open, ignition switch controlled radio wire (10 amp) for the heater / defroster.
Now the question of where to hook up the wipers. They have their own inline 10 amp fuse and are presently connected to the 30 amp headlight fuse.
Here is what I have available:
Main fuse from battery 50 amp

8 fuses in the fuse block marked as follows
Hazard 25 amp
Headlights 30 amp
Stop / horn 20 amp
Coil 25 amp
Turn /wipers 20 amp
Radio 10 amp
Gauges 10 amp
Fuel pump 15 amp
These add up to 155 amps. All fed through a 50 amp fuse. Makes no sense to me.
Any idea of the best place to put the wipers?
Thanks for all of the feed back.
John

Where on earth did the fuse block and wiring harness come from? They don't seem to be closely related to a 1953 truck.

might try putting the wipers where it says 'wipers' sounds like you got an aftermarket multi-circuit harness?

don't bother adding fuses up, a fuse is a safety to insure that the device can't draw more than that max amount, which will relate to how heavy the wire gauge is .... doubt you have a fused coil, doubt you have an electric fuel pump, you've already said you won't have a radio, and you don't have any electric on your gauges but the lights.... unlikely anyo f the rest will be drawing more half of the fuse rating, and if a bunch of them went out at the same time the main fuse would likely blow, so have spares for every size in the glove box - and originally these trucks didn't have a "main" fuse, all the individual circuits are fused at their particular rating

Bill

This is definitely an after market system. The guy I brought it from also must had gotten a good deal on heavy red wire because everything is red. Ugh!
Thanks for all the advice. Now to figure which red wire is the one marked Turn / wipers.
John

Turn on a circuit, like wipers, for instance, and start pulling fuses until it quits. It's very possible that you can eliminate, or consolidate circuits to free up some of those fuses for other purposes. Fuses protect wires, not the end item. If a heater blower motor shorts out, it's toast anyway. The fuse just prevents the wire from burning out when there's a heavy current draw or a short. An 18 gauge wire, for instance, needs about a 7.5 amp fuse, max. A 16 gauge wire can handle 10 amps or so, 15 amps for a 14 gauge, etc. Go with about a 20% to 50% overload capability for any circuit- - - - -If the accessory draws 10 amps, for instance, wire it with 14 ga., and use a 12-15 amp fuse.
Jerry

Is there any reason that I can't connect the aftermarket wipers that have their own inline 10 amp fuse to the "hot" side of my ignition switch as I have determined that this wire is always hot if the main 50 amp fuse is installed even with all other fuses removed from the fuse block?
John

yes John, that would work fine, fuse blocks are just a way to avoid having a bunch of inline fuses cluttering things up under there, the important thing is that the devices be fused

Bill

Now I think that I am good to go.
Thanks all!
John