On older trucks (mine's a '75) the stock wiring harness spits out three wires down near the starter. Two of the wires are Black with White stripe (BW). One of the BW wires is thicker than the other (Big BW). Big BW brings +12v from the key ignition switch, and Small BW takes it from the starter solenoid switch to the (+) coil terminal to by-pass the ballast resistor during cranking. The solenoid switch on the old starter ensured that current was delivered to the (+) coil terminal ONLY when cranking.
The gear reduction starter does not have a terminal for Small BW. It has no solenoid switch for +12v output. When I installed my GR starter several years ago, I just taped-off Small BW's plug and left it dangling. Thus, the GR starter did not supply +12v to the (+) terminal of the coil during cranking. This was never much of a problem for me, perhaps because my battery was very strong, it never gets too cold where I live, or the ignition system was strong enough to plow through the ballast resistance even during cranking.
But lately, I noticed that it didn't start so well in the cold. I studied the wiring diagrams (Haynes mis-labels Small BW as BY in the FJ40 diagrams but gets it right in the FJ55 diagrams. Go figure). I noticed the resistor by-pass circuit and wondered if I could just jumper Big and Small BW to bring +12v to the coil during cranking. I didn't think it would work, but I tried it anyway. It didn't work (see previous 2 posts).
So what's needed is a switch that does the same thing the old starter's solenoid did. A relay is the perfect thing.
See First Picture. These are sold as headlight relays at the autoparts houses for about $5.00. You can get them online for under a dollar.
A relay uses one switch to activate another. In this case, I used the +12v from the key switch (Big BW) to turn on the switch (relay) that sends +12v to the (+) coil terminal. (Since it was already there in the harness, I used Small BW to bring the +12v to the solenoid from Big BW down by the starter.) When you let off the key's start position, there's no juice in Big BW, so there's no juice in Small BW, so the relay turns off the circuit that was supplying +12v to the coil. Just like the old starter used to.
I installed the relay to bypass the resistor when cranking, and it starts on less than 1 revolution in 35F weather. Very nice.
How to wire the relay:
See Second Picture. Relay terminals are numbered
30,
85,
86,
87 (and
87a, if it's a double throw relay. If yours has 87a terminal, just ignore it).
85 <---> 86 is the circuit that switches the other circuit on. So it needs voltage on one side and a ground on the other. I brought the +12v into terminal
85. I brought it up from Big BW on Small BW. I grounded
86. So when the key is turned to "Start", this circuit is energized and switches the other one on.
30 <---> 87 is the working circuit which is turned on by the other one (85<--->86). +12v needs to come in one side of the relay and go out the other to the (+) coil terminal. Since +12v is right there on
85 anyway, just jumper it over to
30. Wire
87 to the (+) coil terminal.
That's it. You're done, and starting will be even easier because you have
both a GR starter
and a ballast resistor by-pass circuit that works like Mr. T intended it to work.