Hi- I've read quite a few solution posts about installing a relay to the starter and I'm curious why I wouldn't just replace the ignition switch harness with a new one if that's really what's at fault? I'm facing the same issues on both of my Cruisers and I'm seeing the switch for $76 at
Champion Toyota
thx- Bong
Because it's probably a series of small "failures" over several components that add up to the problem, rather than just one specific component. As parts age, they become less efficient. There is the ignition switch itself, the neutral safety switch on the trans, several connectors here and there. All in all, probably at least a half-dozen spots where resistance has increased. Add that all up and you'll see some significant voltage drop by the time you arrive at the starter solenoid.
You can replace everything and restore it all to brand-new. $$$$$$$$
Or, you can use that weak signal at the solenoid to trigger a relay that will switch a robust 12v right from the battery into the solenoid. Problem solved for only a few $$.
It's a work-around, but a very cheap, permanent, and effective one. The diesels come with a relay already, I don't know why they didn't put them on the gas trucks.
If you wanted to try and stay original, simply replacing the harness is, in all likelihood, not going to fix it. The actual wires in the harness don't really wear out, but the plugs on the ends of the harness may develop resistance.
Instead, trace out the entire circuit, unplug each plug along the way, and re-insert it several times. This will wipe the contacts and establish a fresh bite, hopefully reducing the resistance at that juncture. do this everywhere along the line.
Disassemble and clean the transmission safety switch, or measure it's resistance and replace it if you like. Clean up the plug going into it as well. All the way to the solenoid signal wire itself, make sure that connection is nice and clean.
Then see if it works. If it doesn't, just put in a relay and forget about it.