Hello everyone. I'm helping my FIL work on a '78. I'm terrible with electrical issues. I want to hook a wire to a terminal on the starter that is hot only when the car is running. Can someone tell me which post on the starter solenoid that I should use? There is no battery in the car so I can't check things with a meter. Thanks in advance.

 

The "R" terminal is 'HOT' with the key in RUN but you cannot use that terminal.



The 'IGN' terminal in the fuse box will give you 12 volts positive when the car is running.

What are you trying to do and what is a FIL?

 

X2 on what are you trying to do? There are other 12V "key on" sources, if that's all you're after.

 

Father in Law. 75 and later don't have a wire on the r terminal of the starter. What are you hooking up, you can use the yellow wiper motor wire for small loads, hot with key on.

 

Yes FIL = Father In-Law

I want a large gauge wire to hook up the electric choke on the carburetor, dual electric fans., etc. The wire needs to be hot in run only. I would use this as a source for anything I connect under the hood that needs a "run only" feed.

 

Usually for fans, a relay is used to switch power to the fan. The coil side of the relay can be powered by an ign or acc source and a temperature switch will ground the relay to make it switch and send power to the fan. The choke is a very small load and can be powered directly from the fuse box ign terminal or the yellow wiper motor wire.

 

This vehicle has the Spal dual fan set up on a DeWitt radiator.. I am using the supplied relays although they do require a 12v switched source from the switched source "run" position. Of course there is also 12v non switched supply to the relays as well which I'm using off of the battery stud on the starter.

I believe I will tap into the ignition feed on the fuse block. Then run a large gauge wire out to a stud in the engine compartment. The stud can be used to power the accessories when the ignition is in the run position. Feedback please.

 

Sure, you can do that as long as you don't apply high current loads to your terminal. Things like the trigger wire to turn an ignition box on, relay coils, an electric choke would be fine. Doing something like directly powering an electric water pump or electric fuel pump would not be a good idea.

 

[QUOTE=Peterbuilt;1591579636]The "R" terminal is 'HOT' with the key in RUN but you cannot use that terminal......

QUOTE]

the 'R' is NOT hot in Run, it is only hot in START. it's purpose is to bypass the resistance feed to the coil normally used while running, thus providing a full 12v to the coil during Starting where the load is higher and RPM is lower to help ensure ignition.

 

[QUOTE=gungatim;1591590280] However, when running the coil is feeding the wire to the r terminal voltage from the ign resistance wire at the coil. At any rate, not a wire to be used for other power needs.

 

Hi '75,
Thank you for correcting my error and reminding me that 1975 and later does not have an "R" wire.

Hi Gungatim,
You are correct that the "R" terminal sends power UP the "R" wire with the key in "START" and thanks again to '75 for explaining that the coil sends 12 volts down the wire in "RUN".

 

except the backfeed from the coil at that point is not 12v, since the coil is fed via the resistance wire, it will backfeed around 9v if it is hooked up. 75 & newer HEI setup will not backfeed that post since there is no R wire and it will not be hot during run at all...pro lem is there are lots of solenoids out there with both posts even if not needed. I just put a starter on a mid-90's caddy where the owner replaced it and put the S on the R terminal not realizing the old one only had 1 terminal.. easy fix...

 

Do NOT do that!!! the wire leading from the typical horn relay going to the battery cable has a fuse link in it, (thinner wire) to help prevent electrical fires from shorts maybe wrecks/accidents.....your problem comes from the fans when running will drop too much voltage through all that wiring, and they tend to not allow a full charge to the battery when running.....you note you house wiring dims a tad when you turn on a space heater in most homes....same thing, a 2-4 volt drop off 110volts hurts nothing, do that with a 25 amp draw from those fans, and to a full on charge of ~14.5 volts, that tapers off to 13.8 via the regulator in the alt. you have a lousy charge on your battery, the guy is just not happy at home in his box..... I do have a short fuse link to the main Spal power wire, a 30 amp fuse would work also...maybe 40 amp.....

I took the main power wire for the Spal fans directly off the alt output stud, up and over to the control relay mounted on top of the shroud, one other wire goes to my control computer from the Fuel Inj. in you case you want another wire to the relay 'hot' side of coil, and to put it to a switched hot, that yellow center wire to the wiper motor was a great suggestion.....the ground side of the coil goes to your sensor, which can be a temp switch on the engine, simple on/off device, it is possible to make with two control relays one for each fan controlled at two different temps, but I did not bother...lazy.....

 

Excellent advice mrvette. I will move those power wires over to the alternator stud.

I won't work on the car for a week or so due to it's distance from me. I will report back on the result of bypassing that relay then.

 

The resistance wire limits current not voltage.
With the motor running a VOM cannot read accurately because the points are opening and closing faster than the meter can register and that is why the positive on the coil or the 'R' terminal show less than 12 volts.

See post #4 on this thread or read 69427's sticky.

https://www.corvetteforum.com/forums...vaoltag-s.html

Street Rat, I apologize for the interruption.

 

LOL, yup the R terminal is 12V (battery voltage) when the points are open and about 6V when the points are closed, but a 78 doesn't have points or the wire or the terminal.