I wouldnt want those amps going though an activation switch.
It would be STUPID not to run a relay.

A 30amp would work great.

 

I'd be willing to bet that 80% of the people on this board couldn't pick a relay out of a line up!

Lets take a vote how many people understand a relay and what it does for you?

 

word,alot of people know the term and might have an idea but it seems like alot of ppl i talk to in person dont know truely what it does.

 

Get a pressure switch and put on the BOTTLE. Why bottle? Because you may close the bottle and leave the heater on and have an empty line while you are playing the radio talking with your pals.

Then run the ground wire for the relay coil through it. So, a wire from ground to the pressure switch then a wire from the pressure to the #85 or #86 terminal on the relay. Then a wire from a key on hot 12v source to #85 or #86. If ground is #85 then positive is #86. Vice a versa. Those wires can be relatively small. 16AWG is fine.

Then from a constant 12volt source run at least a 12AWG wire (10AWG will erase all worries) to the #30 terminal on the relay. The another 12AWG wire from #87 terminal on the relay to the positive wire on the heater. Of course, run the same size wire for the ground on the heater as well. It can be directly to ground, but near battery ground is better.

I'd say never use a relay smaller than 30 Amp rated. The more money you put into one the longer it will last. (Contact surface of internal contacts take a beating from arching.)

 

Nice picture. though 85 is used as a "trigger wire" for almost all PCM controled set-ups, and 86 is keyswitched power..

 

http://home.howstuffworks.com/relay.htm

 

Brake fluid and relays dont play well together....
Finally got some new ones and replaced these with...





When i was younger i was helping my brother put a sound system in his S-10 and he never knew how to wire a relay up..
It took me quite awhile but i figured it out but they are pretty cool how they work..

 

yeah yeah whatever. It's all about understanding it. It needs 12v dc to make that coil pull the contact closed (or open the normally closed). So, it doesn't matter which is which, but does make it easier to follow general rule as you stated.