🔧 Round Relay → Standard Square Relay Adapter (Wire-In Solution)
If you’ve ever dealt with the older round German relays (Bosch / Hella style used on classic Porsche, VW, BMW, etc.), you already know the problem:
they’re expensive, hard to find, and often no more reliable than modern relays.
This adapter lets you convert to a common, inexpensive square relay, while also giving you far more flexibility than the original setup.
⚠️ IMPORTANT: This is a wire-in product.
You will need to cut off the original round relay connector, which is typically non-serviceable anyway.
💡 Why wire-in is actually better
Replacement round relay connectors are shockingly expensive:
• OEM Porsche round relay pigtail: ~$100
• Not available as a proper “kit”
• Forces you to:
– Use butt connectors
– Accept fixed wire colors
– Accept fixed wire gauge
– Accept someone else’s wire layout
With this adapter, you choose:
• Your wire colors
• Your wire gauge (up to 10 AWG)
• Your routing and layout
• Your terminal quality
Cleaner, stronger, and far more serviceable long-term.
✅ What this adapter does
• Converts round / cylindrical German relay setups to modern square (ISO) relays
• Eliminates reliance on rare and expensive round relays and connectors
• Makes future relay replacements cheap and widely available
🧱 Construction & Materials
• 3D printed from ABS plastic (FDM)
• Chosen for heat resistance, toughness, and vibration durability
• Designed specifically for automotive environments
ABS temperature limits (typical FDM):
• Continuous service: ~80–90°C (175–195°F)
• Short-term exposure: ~100–105°C (212–220°F)
• Well within limits for relay panels and engine bay electrical areas
⚡ Electrical Details
• Accepts standard 1/4" (6.3mm) female spade terminals
• Proper terminal retention and locking
• Fits wire sizes up to 10 AWG
• Kit includes 5 spade terminals (18–14 AWG)
Amperage considerations:
• Housing is non-conductive
• Current capacity depends on relay rating, terminal quality, and wire gauge
With appropriate wiring and terminals, this setup comfortably supports 30–40A circuits
(fuel pump, headlights, horns, fans, etc.)
🔁 5-Pin Flexibility (Major Upgrade)
This is a 5-pin relay socket, so you’re no longer limited to basic relays.
You can now use:
• 87a (normally closed) circuits
• Relays with built-in fuses
• Time-delay / timer relays
• Solid-state relays
• PWM-capable relays
• Other specialty ISO relay formats
These options simply don’t exist with the original round relay setup.
🔩 Mounting
• Adapter secured with included ABS nut
• Thread: M30 × 2.0
• Hex size: 35mm
• Locks solidly in place — no zip-ties, no movement
• Fits common round relay panel with min 30mm max 34mm hole, max bulkhead thickness of 2.5mm
This was designed to solve a real-world problem I ran into myself — keeping classic cars reliable without being locked into obsolete electrical parts.
Happy to answer questions or discuss specific applications.
🔧 Round Relay → Standard Square Relay Adapter (Wire-In Solution)
If you’ve ever dealt with the older round German relays (Bosch / Hella style used on classic Porsche, VW, BMW, etc.), you already know the problem:
they’re expensive, hard to find, and often no more reliable than modern relays.
This adapter lets you convert to a common, inexpensive square relay, while also giving you far more flexibility than the original setup.
⚠️ IMPORTANT: This is a wire-in product.
You will need to cut off the original round relay connector, which is typically non-serviceable anyway.
💡 Why wire-in is actually better
Replacement round relay connectors are shockingly expensive:
• OEM Porsche round relay pigtail: ~$100
• Not available as a proper “kit”
• Forces you to:
– Use butt connectors
– Accept fixed wire colors
– Accept fixed wire gauge
– Accept someone else’s wire layout
With this adapter, you choose:
• Your wire colors
• Your wire gauge (up to 10 AWG)
• Your routing and layout
• Your terminal quality
Cleaner, stronger, and far more serviceable long-term.
✅ What this adapter does
• Converts round / cylindrical German relay setups to modern square (ISO) relays
• Eliminates reliance on rare and expensive round relays and connectors
• Makes future relay replacements cheap and widely available
🧱 Construction & Materials
• 3D printed from ABS plastic (FDM)
• Chosen for heat resistance, toughness, and vibration durability
• Designed specifically for automotive environments
ABS temperature limits (typical FDM):
• Continuous service: ~80–90°C (175–195°F)
• Short-term exposure: ~100–105°C (212–220°F)
• Well within limits for relay panels and engine bay electrical areas
⚡ Electrical Details
• Accepts standard 1/4" (6.3mm) female spade terminals
• Proper terminal retention and locking
• Fits wire sizes up to 10 AWG
• Kit includes 5 spade terminals (18–14 AWG)
Amperage considerations:
• Housing is non-conductive
• Current capacity depends on relay rating, terminal quality, and wire gauge
With appropriate wiring and terminals, this setup comfortably supports 30–40A circuits
(fuel pump, headlights, horns, fans, etc.)
🔁 5-Pin Flexibility (Major Upgrade)
This is a 5-pin relay socket, so you’re no longer limited to basic relays.
You can now use:
• 87a (normally closed) circuits
• Relays with built-in fuses
• Time-delay / timer relays
• Solid-state relays
• PWM-capable relays
• Other specialty ISO relay formats
These options simply don’t exist with the original round relay setup.
🔩 Mounting
• Adapter secured with included ABS nut
• Thread: M30 × 2.0
• Hex size: 35mm
• Locks solidly in place — no zip-ties, no movement
• Fits common round relay panel with min 30mm max 34mm hole, max bulkhead thickness of 2.5mm
This was designed to solve a real-world problem I ran into myself — keeping classic cars reliable without being locked into obsolete electrical parts.
Happy to answer questions or discuss specific applications.
