HELLA Horn Wiring Harness, Vintage Fog Lights, and an N20 Timing Chain Kit: What One Parts Buyer Learned

Last November, a grille shell landed on my desk at 8:15 in the morning. Our shop lead had taped a note to it: “Need Hella period fog. Order harness and relay before Friday.”

I’m the office administrator for a 21-person shop that does automotive repair, restoration, and light marine service. I manage parts purchasing—roughly $60,000 a year across 13 vendors. My official title sounds calm. The unofficial part is decoding notes like that one before technicians run out of patience.

That one grille shell, plus two other jobs already in the queue, forced me to deal with four of my least-favorite tasks in a single week: identifying a Hella horn wiring harness, finding vintage Hella fog lights, ordering an outboard water pump impeller, and understanding why an N20 timing chain kit purchase starts with the question of where the camshaft is located.

By Friday, I realized all four problems had the same root cause. Accurate identification matters more than a good price.

First, the HELLA Horn Wiring Harness

The truck had dual aftermarket Hella horns, but the original wiring wasn’t designed for them. If your stock horn circuit was built before relay modules were common, asking the old horn switch to carry the whole current load is never my first choice.

That’s where a Hella horn wiring harness comes in. The Hella-style harness includes a relay, a fuse, and pre-routed wiring, so the battery supplies power to the horns instead of pulling everything through the steering column switch.

I made the classic rookie mistake on this one. The first “compatible” harness I ordered had no relay and a pair of connectors that fought with our grounds. It was about $16 cheaper than the Hella unit. The technician spent maybe 45 minutes—no, probably closer to two hours by the time he unwrapped the 40-year-old tape—checking why the horns sounded weak. The part wasn’t broken; it was just the wrong solution. We ordered the HELLA setup and the problem disappeared.

To be fair, if you’re wiring one compact horn into a modern car that already has a relay, you may not need a full harness. But for a nearly 50-year-old truck with dual aftermarket horns, the Hella horn wiring harness was the right call.

Vintage HELLA Fog Lights Are a Different Kind of Search

While the harness debate was going on, I was also hunting for vintage Hella fog lights. That search is not a simple catalog lookup. The brackets changed over the years, the lamp connectors changed, and the reflector condition is almost impossible to verify from a blurry listing photo.

We found a period-correct pair and bought them anyway. That was partly because the owner was specific about the look and partly because they were the fifth pair I had found in a month. When they arrived, one mounting tab was cracked and one reflector had coffee-colored corrosion spots. Not the end of the world for a shop that restores things, but it added hours and another parts order.

Here’s the honest limitation part: my experience with vintage Hella lights is based on maybe ten shipments over three years. If you’re building a show truck and need untouched originals, my advice is not to settle for a “project pair.” If you’re building a weekend driver, a clean used set with new bulbs and fresh wiring is usually fine. Different goals, different buying rules.

And Then an Outboard Water Pump Impeller

In the middle of that, our marine technician asked me to order an outboard water pump impeller. A boat had been overheating at idle, and the owner wanted a quick answer. I typed the year and model into the supplier site, saw the kit, and hit buy.

Wrong. Well, not completely wrong—same motor family, but the wrong pump revision. The manufacturer changed the water pump housing at a serial-number break that I didn’t check. I matched the visible model tag, but not the serial range. That’s the same mistake I made with the harness: I ordered by what something “fits” instead of by the specific version.

The return process cost me about 30 minutes and the marine tech was polite enough not to make me feel worse about it. The part itself was around $80, I think, but don’t hold me to that. The real cost was the delay and the loss of trust. In a shop, when a part is wrong, it isn’t just an invoice problem. It’s an internal customer problem.

For outboard water pump impellers especially, I’ve learned to ask for the serial number, not just the model. “Fits 2006 90 HP” is not a part number. It’s a starting point.

The N20 Timing Chain Kit and a Question That Looks Simple

The third job that week was a BMW with the N20 engine. The engine builder asked me to price an N20 timing chain kit. Before that order could go anywhere, I had to answer a question that sounds like a trivia question but isn’t: where is the camshaft located?

Direct answer: The camshaft is located in the cylinder head, above the combustion chambers. In a BMW N20, there are two camshafts in the head—one for the intake valves and one for the exhaust valves. The timing chain connects those camshafts to the crankshaft below.

Why does that matter when buying an N20 timing chain kit? Because the chain kit has to cover the full route from the crankshaft up to both camshafts, including the guides and tensioners. If you only order a chain and ignore the rest, you’re halfway to a second repair. And if the camshafts aren’t locked into their correct positions during installation, what should have been a timing chain replacement can turn into a much larger engine problem.

The kit we ordered included the chain, guide rails, tensioner, gaskets, and the associated fasteners. I’m not going to recommend a specific brand here because I only have one data point. What helped more was asking suppliers two questions: does the kit include the full hardware set, and can you verify the serial-number range? If the answer is only “fits N20,” that’s a red flag to me now.

What I’d Do Differently Now

• Check the serial range on mechanical parts, not just the year and model.
• Ask whether a wiring kit actually includes a relay before assuming “harness” means the complete solution.
• Pay attention to the difference between “fits” and “specifically matches this component revision.”

Bottom line? I don’t believe in universal “best” parts. I believe in matching the right product to the right vehicle revision. A Hella horn wiring harness made sense for our restoration truck because of its old wiring and dual aftermarket horns. It would be overkill in some other situations. The same logic applied to the outboard water pump impeller and the N20 timing chain kit.

If you’re doing this kind of buying for a living, take the extra five minutes to ask for the serial number, the OE reference, and the relay details. It’s cheaper than the rushed correction later.