Cooling Fans and Harnesses Universal FAQs
4 min read
BP Automotive — Fan Harness FAQ #
Purpose: Answer the fan-harness questions that apply across platforms so customers can self-serve before emailing.
Platform-specific FAQs (truck/SUV two-speed, F-body, Gen V PWM, aftermarket DFK) can be added as separate drill-down sections later.
Start here: how BP Automotive fan harnesses fit your swap #
BP Automotive fan harnesses and relay kits add reliable electric-fan control for GM swaps and supported factory-style applications.
Choose the harness or relay kit around:
- The fan assembly you are using (connector and style)
- The control method (two-speed relay, single-speed, Gen V PWM, etc.)
- The fan’s running and starting current — not only the engine year or vehicle
These FAQs stay universal. If your question is about a specific fan style or platform, use that platform section on the site once it is published.
Which BP Automotive fan harness or relay kit is right for my fans? #
Choose by fan type, connector, control method, and maximum starting/current demand.
- Factory 2005–2013 GM truck/SUV fans generally use the 1017-style harness and are fused at 40 amp for each fan.
- LS1/LT1 F-body fans are a natural match for our fan kits because they come with LT1/LS1 fan connectors already installed. These fans are fused at 40 amp for BOTH fans. 20 amp each.
- Traditional aftermarket fans may use SRK-001, SRK-002, or SRK-003 when their current demand is within the kit rating.
Send us the fan part number and the manufacturer’s running and starting-current information if you want us to confirm the best fit.
Can I add a manual fan switch and still keep PCM control? #
Yes. Manual switches can be added to the separate fan-control inputs while leaving the PCM connections in place.
For a two-speed setup, use one switch for each control input; high speed requires both switches. Manual operation should not be used continuously at highway speed — it can overwork the fans and relays. BP Automotive STRONGLY advises against manual fan switches in street-driven vehicles. BP Automotive does not warranty any fan harness that has been wired with manual switches.
What does the fan wiring on my BP engine harness actually control? #
In a typical standalone LS harness, the fan wires are relay-control circuits; they do not power the fan motors directly.
- The PCM supplies the ground-side control for the fan relays
- The relay kit (or customer-supplied relays) carries fan power
Use the installation manual for the correct relay terminals and keep the high-current fan feed separate from the PCM control wiring.
Why do my fan relays click, buzz, or cycle repeatedly? #
Repeated relay clicking is commonly caused by incomplete or incorrect fan calibration, especially when the PCM is still configured for another output or the fan enable/disable settings overlap.
Correct the tune first, then verify the relay and harness installation against the manual.
Why do my fan fuses blow when the fans start? #
A fan may show an acceptable running demand but draw much more during startup, particularly when two fans start together at high speed.
If a fuse opens, do not install a larger fuse in the existing block — that can overload the terminals, relay, wiring, or fuse block. You will need to either purchase fans that draw less amperage or upgrade to a fan harness that is rated for the amperage your fans draw.
Can the PCM turn the cooling fans on when the A/C is running? #
Yes, when the application has the correct A/C pressure-sensor (transducer) installed and the PCM is calibrated for fan control.
The PCM can request fan stages from coolant temperature and A/C system pressure. The compressor clutch signal alone is not the preferred way to run the fans, as this will cause premature cooling fan and/or harness wear or damage.
A trinary switch can be used but is far less accurate than using the A/C Pressure Sensor.
What fan settings should my tuner use? #
Start with a factory calibration from a GM vehicle that used the same style of electric-fan system, then adjust only as needed for the engine and A/C system.
- Keep the fan settings as close as possible to GM factory settings as possible. GM spent millions of dollars to develop the best strategy.
- DO NOT set the fan temperatures below 200*. This can cause premature cooling fan wear, and LS-Based engines were designed from the ground up to run a 200+ degrees.
BP fan tuning is available when you want the file reviewed for the complete set of fan tables, not only the on-temperature values. BP Automotive will provide a price quote for any changes to a file we did not provide tuning for.
Can I use a BP fan relay kit with a standalone harness or aftermarket ECU? #
Yes, when the ECU provides two programmable ground-side outputs for low and high fan control.
Connect the relay kit’s power and ground as instructed, keep the two control inputs separate, and program the ECU for the fan strategy being used.
With a one-output ECU, do not tie both inputs together unless you intentionally want high-speed-only operation; a separate fan controller WILL be the better solution. Causing both fans to come on at high speed every time they are activated creates a lot of inrush current and strain on your charging system.
What is different about a direct-fit harness versus a standalone harness? #
Direct-fit S10 harnesses are built around the vehicle’s factory fuse/relay center and includes a fan harness with the engine harness.
Direct-fit F-Body harnesses are built around the vehicle’s factory fuse/relay center and will utilize the original cooling fan wiring.
A standalone engine harness has its own fuse block and typically provides fan-relay control wires while the fan relay kit is purchased separately.
The two styles are not interchangeable — identify the harness type before splicing or ordering a fan kit.
Scope note #
This FAQ covers universal fan-harness questions that apply across platforms.
It does not replace:
- The product installation sheet for your specific kit
- Platform-specific details (truck/SUV two-speed, F-body, Gen V PWM, aftermarket DFK)
