Tuesday, 16 June 2026

REPLACING FRONT INDICATORS ON A CLASSIC HYMER

 

REPLACING FRONT INDICATORS ON A CLASSIC HYMER

One of the commonest questions on the Classic Hymer group is:

"I've broken a front indicator. Where can I get another one?"

Unfortunately, there is no easy answer.

The original Hymer indicators

The original front indicators fitted to pre-1995 Classic Hymers were manufactured for Hymer by Hella and are now obsolete.

Early vans used amber lenses with clear bulbs, while later vans used clear lenses with amber bulbs. Physically they are the same and can be interchanged, although a matching pair obviously looks best.

Because originals are no longer available, good second-hand examples command surprisingly high prices and are often sold within hours. There have even been reports of complete indicator units being stolen from parked vans.



Original yellow indicator

Option 1 - Bolt on Bits (Recommended)

For most owners, this is now the best solution.

A UK company called Bolt on Bits has developed a replacement system using a modern Hella lamp combined with a custom-made surround designed specifically for Classic Hymers.

The result looks neat, fits properly and avoids the gaps associated with other alternatives.

Available in both amber and clear versions.

Advantages:

  • Good cosmetic appearance.

  • Direct replacement.

  • Readily available.

  • New parts.

Disadvantages:

  • Most expensive option.

  • Approximately £150 per pair.

An owner with one broken original can often offset part of the cost by selling the remaining good original to another enthusiast.



Option 2 - Optare / Hella replacement units

A cheaper alternative uses a Hella indicator also fitted to Optare buses and other commercial vehicles.

Common part number:

HELLA 2BA 004 119-001

These are widely available from commercial vehicle suppliers and online.

They are slightly smaller than the original Hymer units and require some modification to fit. The result is perfectly serviceable but leaves a small gap around the lamp.

Many owners have used these successfully, particularly as a temporary or budget solution.

Advantages:

  • Cheap.

  • Easy to obtain.

  • Good emergency replacement.

Disadvantages:

  • Not an exact fit.

  • Requires modification.

  • Small visible gap around the lamp.



[PHOTO - Optare fitted to Classic Hymer]

Which should I choose?

For most owners:

Bolt on Bits is the best long-term solution.

If cost is the main consideration, or you simply need to get back on the road, the Optare/Hella units work perfectly well and many owners are happy with the appearance.

A final tip

If you damage an original indicator, don't throw the pieces away.

Even badly cracked lenses can sometimes be carefully repaired or used as patterns for future restoration work.

And if you ever remove a good original pair, look after them. They have become one of the harder Classic Hymer parts to replace.


Summary

Original Hella Hymer indicators

  • Obsolete.

  • Rare.

  • Expensive second-hand.

Bolt on Bits

  • Best appearance.

  • Purpose-made surround.

  • Recommended.

Optare/Hella

  • Cheap.

  • Readily available.

  • Slightly undersized but perfectly usable.

As with many Classic Hymer parts, there is no perfect answer, but fortunately there are now practical solutions that can keep these vans on the road for many years to come.

Sunday, 31 May 2026

Mercedes Glowplugs

 

Mercedes OM602 Glow Plug Problems and Diagnosis

Introduction

Glow plug faults are one of the most common starting problems encountered on older Mercedes-based Hymers fitted with the OM602 five-cylinder diesel engine.

Many owners confuse glow plugs with spark plugs. Diesel engines do not use spark plugs. Instead, glow plugs act as electric heaters, warming the combustion chambers during cold starting. Once the engine is running, the glow plugs have little or no further function until the next cold start.

A healthy glow plug system is essential for reliable starting, particularly in winter.


How the System Works

When the ignition key is turned to the pre-heat position, the glow plug relay supplies power to each glow plug for a few seconds.

The dashboard glow plug warning lamp illuminates while the plugs are heating. Once sufficient temperature is reached, the lamp goes out and the engine can be started.

Mercedes used a relatively sophisticated system on the OM602 engine. Each glow plug has its own connection from the relay box rather than all plugs being connected to a common bus bar. This allows the control system to detect certain failures and warn the driver.


Typical Symptoms

Common symptoms of glow plug system problems include:

  • Glow plug warning lamp behaving abnormally.

  • Warning lamp staying on after starting.

  • Warning lamp not illuminating at all.

  • Difficult starting in cold weather.

  • Excessive white or grey smoke immediately after starting.

  • Rough running for the first few seconds after start-up.

  • Gradually worsening starting performance over months or years.

A single failed glow plug may not prevent the engine from starting, particularly in warm weather. However, once one plug fails, the remaining plugs are often not far behind.


Glow Plug Life Expectancy

In normal use, glow plugs typically last many years. Experience suggests that around ten years is a reasonable lifespan.

When one plug fails, it is generally sensible to replace the complete set rather than changing individual plugs one at a time.

Cheap pattern parts often prove to be a false economy. Bosch and Beru plugs are generally regarded as the safest choice for long-term reliability.


Testing the Glow Plugs

A simple resistance check can often identify failed plugs.

Disconnect the output connector from the relay box and measure resistance between each glow plug terminal and earth.

Typical readings are approximately:

  • 0.7 to 1.2 ohms

A reading significantly higher than this, or an open circuit, usually indicates a failed plug.


The Glow Plug Relay Box

The relay box is mounted in the engine bay and contains the heavy-current switching required to power the glow plugs.

Although generally reliable, relay failures do occur.

Common faults include:

  • Burnt relay contacts.

  • Failed internal electronics.

  • Blown strip fuse.

  • Corroded power connections.

  • Damaged wiring.

A large strip fuse is mounted on top of the relay box. This is easily inspected and should be checked before condemning the relay itself.

With the ignition switched on, battery voltage should be present at the glow plug outputs during the pre-heat cycle.


An Interesting Real-World Fault

One owner experienced progressively worsening starting problems over the course of a year.

Testing showed:

  • All glow plugs measured correctly.

  • Temperature sensor tested correctly.

  • Relay appeared to operate.

  • No glow plug warning lamp fault was displayed.

The relay pulled in but immediately dropped out whenever load was applied.

After extensive investigation, the cause was found to be a nearly broken power connection at the starter motor terminal. The cable had fractured inside the crimp terminal and could pass enough current to operate the relay, but not enough to power the glow plugs.

The fault was eventually cured by repairing the terminal connection.

This serves as a useful reminder that wiring and power-supply faults can mimic relay failure.


Replacing Glow Plugs

Replacement is straightforward for an experienced mechanic but can be awkward on older vehicles.

Points to note:

  • Access to the front cylinders can be difficult.

  • Correct sockets and extensions are required.

  • Old plugs may be tight.

  • Excessive force can occasionally break a glow plug during removal.

Although broken plugs are uncommon, extraction can become a major repair if it happens.

For this reason, replacement is often best carried out by a garage familiar with older Mercedes diesel engines.


Emergency Starting

If several glow plugs have failed and the engine will not start in cold weather:

  • Avoid flattening the starter battery through repeated cranking.

  • Allow the remaining plugs as much heating time as possible.

  • As a last resort, starting fluid may get the engine running.

However, starting fluid should be regarded as an emergency measure only and not as a repair.


Useful Part Numbers

OM602 five-cylinder engine:

Glow Plug:
A001 159 17 01

Glow Plug Relay:
A007 545 99 32

Always verify part numbers against the vehicle VIN before ordering.


Practical Advice

When glow plug problems first appear:

  1. Check the strip fuse.

  2. Check power supply connections.

  3. Test the glow plugs individually.

  4. Inspect relay operation.

  5. Consider replacing the full set of plugs if one has failed.

In many cases the fault will be a failed glow plug. However, relay box faults, poor connections and wiring problems should not be overlooked.

A methodical diagnosis will usually identify the problem without replacing unnecessary parts.


References

  • Mercedes Glow Plug Info and Issues

  • The Mercedes Glow Plug Relay Box

  • Part Numbers Mercedes Glow Plug

  • More Mercedes Glow Plug

  • Deep Dive Into the Relay Box Mercedes Glow Plug