Here is the in-depth write-up that I hope can serve as a how-to for OM617-swapping 96-04 Tacomas/4Runners (and T100's).
I picked up this $600 1997 4Runner 5VZ/A340 4x4 (rear e-locker) with roughly 250k miles and it was SHOT! Completely rusted out even though the body doesn't show it. Destroyed interior. Radiator blew up and mixed trans fluid with coolant to make a milkshake in the trans. Now I haven't read a single report of anyone flushing their trans and successfully driving it after that. Even the ones done under warranty at the dealership with the power flush had trans failure shortly after. Keep an eye on your radiator if you've got an automatic! The PO claims he noticed it right away and had it towed home where I picked it up. I flush the trans, added a new radiator, and put another 30k on the 5VZ! I daily drove it to work, used it to tow the mower trailer around, and even drove it 3 hours into Iowa with the trailer to get a band saw. Did a fair amount of wheeling with it, too, enjoying the rear locker. Eventually, it started losing coolant, so the 5VZ got yanked and sold.
The plan for this has always been for R&D. The only money I have into this rig is the new radiator and mounting the free tires someone was throwing away. Sold the 5VZ to cover the purchase. Can't beat that! I'm currently swapping in an OM617. I'll be using the 4Reigner to test trails I'm cutting in our pasture, as well as haul the tree cutting equipment around. Since the frame is already falling apart, I don't expect to keep this around much longer. I had originally planned to do a TDI swap after the 617, but have since decided not to worry about making TDI adapters for the Toyota Automatics, as the torque converter pilot stub would require turning down, and that is probably too much effort for most people. Once the frame folds in half, I'll pull the 617 back out to go into something long-term, and I'll save the rear axle and trans.
I want to address gauges and LED's, and I think this kind of goes together...
LED's are current technology - halogens are archaic. My gauge cluster had 1 of 3 backlights working. I couldn't see my fuel level or the water temp. I added white LED's for the backlights, which make things clearly visible. https://amzn.to/3ToekRE
The Low Fuel bulb is the same as the backlights, but you can't run an LED there, or it'll always stay on (at least mine did). Shame, because I want that to be bright and in-my-face when it comes on.
The idiot lights are finicky. You can't run an LED for the Charge, or your alt won't charge properly. I also couldn't get the 4x4 to work with an LED. The light has to illuminate, or your 4x4 won't engage (the current has to pass thru the bulb from the switch to the differential - how dumb). If your 4x4 doesn't engage, your bulb may be burned out - now you know!
Cruise also won't work without the bulb illuminated. But it works with an LED - just make sure you install it with the correct polarity (the first time I tried cruise, it didn't work bc I installed the bulb backwards).
My brake light stayed on because my fluid was low. Added a couple drops of fluid and it went off. I have LED's in for the Wait to Start (CEL), Cruise, Hi Beams, O/D OFF, and ECT PWR. I'd probably recommend going with something dimmer for the ECT PWR since it'll likely always be on. Same with the OD OFF. Using an LED for the W.T.S. helps it to illuminate. The Merc glow plug controller commonly puts out a weak, low voltage signal that won't illuminate a halogen bulb, but LED's will still pick up the lower voltage and light up.
I removed the trans temp light since I installed an aftermarket temp gauge in the original sending unit's place. More on that in a second...
Another dumb thing that I hate - the A340 has an actual temp sensor, not just an on/off switch for a light. If you plug into your OBD2, you can read the trans temp! But the idiot light doesn't come on till 300°, which is 50° after your trans was already dead, anyway. Why pay to install a sensor but not give us a gauge to read it, Toyota?
Here's how I installed an aftermarket Glowshift gauge (part # in pic). It's a better thread adapter than the Autometer part. Use the crush washer, not the o-ring. Sucks that you have to loosen the cooler line fitings to get to it, though. Keep in mind that removing the factory temp sensor removes the fail-safe feature that kicks off your AC if the trans temp ever gets too high.
This trans can safely handle at least 220°. I like to see it at 180, which is the operating temp for ATF. But I'll see it stick at 160 while cruising, and I'll see it hit 200 with a heavy foot and lots of shifting in stop/go traffic. I back off and take it easy once it elevates to 200, for longevity of the trans. Excessive heat only means shorter life (so does excessively cold). The stock torque converter could likely be highly improved upon, but it works! If you're pinching pennies, there's no reason you can't just run it. A custom unit from FTI is on my bucket list, though.
Back to LED's! I'd put them in for your overhead lamps! Here're the links:
https://amzn.to/3NT5jPm
https://amzn.to/3fPX4XG
I like both. I don't notice a difference so far between the 2 brands, so longevity will probably be the difference.
Here's before and after shots:
Here are the same bulbs in the map light slots (99-02 have different map lights). They're blinding, but you'll be able to see anything you want.
The ignition cylinder, automatic shifter, HVAC controls, and glove box all use the same bulb. The cig lighter has a goofy proprietary halogen bulb, unfortunately. LED link here:
https://amzn.to/3hsu2he
My shifter bulb was burned out and I couldn't see which gear it was in at night. Since the 96-98 don't have the indicator in the gauge cluster, it was challenging to drive at night. Not anymore!
I'll pick back up on gauges in a 2nd post.