If you want to repair a vehicle, you'll need to collect and craft various parts. And if you're curious about the "best" way to repair a vehicle when these tweaks are installed, here's a simple summary of everything:

• There are several methods to improve your wrenching/harvesting in the game: The "Salvaging Operations" perk, the "Salvage Tools" action skill, and the in-game buffs (such as the "Hackers" candy) are all very useful, but keep in mind that they will ONLY increase the AMOUNT of items you find; so for example, "+48% would mean that you'd find 14 Scrap Iron instead of 10" (and as you can see, the game always rounds the boosted value downwards, such as "14.8 becomes 14" in this example). However, NOTHING in game will EVER improve the CHANCES of getting an item, which means that a "50% drop rate when harvesting" is forever a "50% drop rate". In other words, those buffs will reduce the overall farming time by giving you more items, but won't improve your drop chances.
• Furthermore, due to the game always "rounding downwards", you'll need to get "+100% yield" (doubling the loot) or higher, if you want to receive 2x of all "rare" items that you'd normally only get 1x of (such as engines). Because "+98%" (in other words, "1.98 engines") would still get rounded down to "1 engine" by the game. You can actually combine the salvaging perk, action skill and buff foods to reach the double yield threshold, if you put some effort into reaching it, but it's barely worth worrying about that since there are improved ways to get engines thanks to the Anti-Bullshit tweaks.
• Another very important rule, is that you should only wrench the "living" (lootable and/or repairable) vehicles, since the "dead" (non-interactive) vehicles cannot drop any interesting parts. Basically, if you see a "dead" shell of a vehicle, such as a car without wheels, then you can immediately see that it's useless. That's because vehicles that are "dead" or stripped-down basically means that they've "already been scavenged or destroyed", and will therefore only contain basic things such as scrap metals and polymers.
• Get the vehicle maintenance manual from research, traders or looted schematics.
• The wheels for your vehicle type should be researched and then crafted from scratch (because it's barely worth destroying vehicles since they all have an extremely low chance to drop wheels), although you might sometimes find wheels or their schematics in loot or at traders (they're worth buying if you see them).
• Engines should be looted from "Pass-N-Gas" loot crates, from general loot (car trunks, damaged battery banks, garage boxes), or from traders, but you can also get them from wrenching vehicles and industrial machines if it's an emergency and you haven't found any yet (but please try to avoid destroying vehicles if there are other players on the server, since they need repairable vehicles too).
• Get the Headlights, Ball Bearings and Lead Batteries from wrenching vehicles, mainly from cars and trucks, but stop when you've found enough since the drop rates have been increased (so you should leave some for other players).
• Craft the remaining, generic materials, such as various metal plates.
• Then simply find the vehicle of your dreams and repair it!