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Your trunk won't latch shut, and your car won't start and now you're staring at a repair bill you didn't plan for. These two problems, a faulty trunk latch and a bad starter motor relay, are more common than most drivers realize. Knowing the real cost to fix them helps you avoid overpaying at the shop, spot a dishonest quote fast, and decide whether it's a DIY job or something that needs professional hands.

What exactly is a trunk latch fault, and what causes it?

The trunk latch is the mechanical or electronic lock that holds your trunk shut. On most modern cars, it works with a motor and a sensor that talks to the body control module. When it fails, the trunk might not close, won't pop open with the key fob, or shows a warning light on the dash.

Common causes include a worn-out latch motor, broken wiring between the trunk and the car body (especially where the harness flexes near the hinges), a blown fuse, or corrosion inside the latch assembly. Water intrusion through old trunk seals is a frequent but overlooked cause.

What does a starter motor relay fault mean?

The starter relay is a small electrical switch that sends power from the battery to the starter motor when you turn the key (or push the start button). When it fails, you turn the key and hear a single click or nothing at all. The engine won't crank.

A bad relay, corroded terminals, weak battery connections, or a wiring issue between the ignition switch and the starter solenoid can all cause this fault. Sometimes the problem is the relay itself. Other times, the wiring or the starter motor is the real issue.

For a deeper look at how these two systems connect electrically, you can read this diagnosis guide covering trunk and starter wiring faults.

How much does it cost to fix a trunk latch?

The cost depends on what's broken and what you drive.

Trunk latch assembly replacement (parts only): $30–$150 for most vehicles. Luxury brands like BMW or Mercedes can push the part cost to $200–$400.
Labor: $50–$150 at most shops. The job usually takes 30 minutes to an hour.
Wiring repair (if the harness is damaged): $100–$300 depending on how hard the wiring is to reach. Trunk hinge areas are notorious for wire breaks because the cables flex every time you open and close the trunk.

Overall, expect to pay $80–$400 for a trunk latch repair on a typical sedan or SUV. If the body control module needs reprogramming after the fix, add another $50–$100.

How much does it cost to fix a starter motor relay fault?

Starter relay replacement (parts only): $10–$50. This is one of the cheapest parts in the starting system.
Labor for relay swap: $30–$80. On many cars, the relay sits in the fuse box and takes minutes to replace.
Wiring or connector repair: $100–$350 if the fault is in the wiring between the ignition switch, relay, and starter.
Starter motor replacement (if the relay wasn't the only problem): $200–$600 total for most vehicles.

A straightforward relay replacement usually costs $40–$130 out the door. But if testing reveals a wiring fault or a bad starter motor, the bill climbs. Getting a proper professional electrical fault analysis before parts are thrown at the problem can save you from paying for repairs you don't need.

Can these two faults be related?

Yes, and it happens more than people think. Both the trunk latch and the starter relay share ground points and, on some vehicles, sit on the same body control circuit. A corroded ground wire or a damaged section of harness can cause both problems at the same time.

If your trunk won't open with the remote and the starter clicks but won't turn over, there's a good chance you're dealing with one shared electrical fault rather than two separate broken parts. Fixing just one without checking the other often means the second problem comes back days later.

What are the most common mistakes people make with these repairs?

Replacing the relay without testing it first. A $10 relay swap sounds cheap, but if the wiring is the real problem, you've wasted time and money.
Ignoring the trunk hinge wiring. Broken wires in the trunk hinge area are one of the top causes of trunk latch failure on cars older than five years. Shops that skip this check end up replacing good latch assemblies.
Not checking grounds. Both systems need clean, tight ground connections. A single rusty ground bolt can mimic a dead relay or a broken latch motor.
Assuming the starter motor is dead when the relay clicks. A click doesn't always mean the starter is gone. It often means the relay is working but can't pass enough current because of a wiring fault upstream.
Using cheap aftermarket relays. Some budget relays have thinner internal contacts and fail within months. Spending an extra $5–$10 on an OEM or quality-brand relay pays off.

How can you save money on these repairs?

Test before you replace. A multimeter and a wiring diagram can confirm whether the relay, latch motor, or wiring is the issue. Many auto parts stores will test relays for free.
Check fuses and grounds first. These cost nothing to inspect and fix, and they solve more problems than most people expect.
DIY the relay if you're comfortable. Swapping a starter relay is one of the easiest car repairs. No special tools needed just pull the old one out of the fuse box and push the new one in.
Bundle the diagnosis. If both faults appeared around the same time, have them diagnosed together. Separate trips to the shop mean double diagnostic fees.

You can learn more about the specific wiring and electrical patterns behind both failures in this detailed breakdown of trunk latch and starter relay fault costs.

When should you see a professional?

If you've swapped the relay and the problem comes back, or if the trunk latch works sometimes but not always, the fault is likely in the wiring and tracing wiring faults on a loaded car takes experience and the right diagnostic tools. A shop with electrical diagnostic capability (not just parts-swapping ability) will find the root cause faster and cheaper than guessing.

According to AAA's auto repair estimates, diagnostic labor for electrical faults runs $100–$150 per hour at most independent shops. Paying for an hour of solid diagnosis almost always costs less than replacing parts that weren't broken.

Quick checklist before you book a repair

✅ Check all related fuses with a test light or multimeter
✅ Inspect ground points for corrosion or looseness
✅ Look at the trunk hinge wiring for visible damage or exposed copper
✅ Test the starter relay with a multimeter or swap it with a known-good one from the fuse box
✅ Note whether both problems appeared at the same time shared root cause is likely
✅ Get a written estimate that separates diagnostic time from repair labor
✅ Ask the shop if they checked wiring before recommending part replacement

Bottom line: Most trunk latch repairs cost $80–$400 and most starter relay fixes cost $40–$130. But the real savings come from proper diagnosis making sure you're fixing the actual fault, not just the symptom.