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Low Oil Pressure Switch 87-805605A1 – MerCruiser 3.0–7.4L
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How to Match This Part
This aftermarket low oil pressure switch replaces MerCruiser / Quicksilver 87-805605A1. It threads into an oil-gallery boss on MerCruiser sterndrive and inboard engines and sends a signal to the audio warning system when oil pressure falls too low.
Match this part in this order:
1. OEM number on the removed switch or in your parts catalog (87-805605A1, 38559, 817169, or F708940)
2. Engine family and displacement — MerCruiser sterndrive or inboard calling for this switch in the 3.0L–7.4L range
3. Thread and terminal — 1/8-27 male pipe thread with a single 10-32 stud terminal
Identify the form from the product images: zinc-plated tapered body, black insulator cap, single brass stud with nut and lock washer, and reddish-brown thread sealant on the male pipe threads. If your original unit has two terminals, a spade connector, or is a variable-resistance gauge sender rather than an alarm switch, it is a different component.
Part Number Cross-Reference
Use this table to confirm equivalent part numbers across OEM and aftermarket brands. Mercury also catalogs the same switch without the leading prefix as 805605A1.
| Type | Brand | Part Number | Notes |
|---|---|---|---|
| OEM | Mercury MerCruiser / Quicksilver | 87-805605A1 | Current switch assembly; also listed as 805605A1 |
| OEM | Mercury MerCruiser | 38559 | Superseded by 805605A1 |
| OEM | Mercury MerCruiser | 817169 | Superseded by 805605A1 |
| OEM | Mercury MerCruiser | F708940 | Earlier catalogue number in the same supersession chain |
| Aftermarket | Sierra | OP22900 | Direct aftermarket replacement |
Part numbers are listed for identification only. This is an aftermarket part manufactured by JLM Marine and is not sold as a genuine Mercury or MerCruiser component.
Compatible Engine Models
Confirm your engine model and serial number before ordering. On MerCruiser sterndrive and inboard engines, the identification plate and serial number are on the engine itself — typically on the cylinder block or flame-arrestor cover — not on an outboard transom bracket. Cross-check with the Mercury Parts Diagrams for your MerCruiser engine group.
This switch serves the low oil pressure audio warning circuit. It is not the variable-resistance sender that drives an oil pressure gauge.
| Brand | Application | Displacement | Notes |
|---|---|---|---|
| MerCruiser | Sterndrive engines calling for 87-805605A1 | 3.0L–7.4L | Audio warning system signal |
| MerCruiser | Inboard engines calling for 87-805605A1 | 3.0L–7.4L | Audio warning system signal |
Technical Specifications
| Specification | Value |
|---|---|
| Part type | Low oil pressure switch (audio warning) |
| Primary OEM number | 87-805605A1 |
| Thread size | 1/8-27 male pipe thread |
| Terminal type | 10-32 threaded stud, single terminal |
| Function | Signals the engine audio warning system on low oil pressure |
| Form | Zinc-plated tapered body, black insulator, sealant on pipe threads |
Installation Guide
1
Allow the engine to cool fully. Disconnect the battery negative cable before working on the warning circuit.
2
Label and remove the warning-system wire from the old switch stud. Unscrew the old switch and compare its thread and terminal to this 1/8-27 / 10-32 unit. Do not force a mismatched thread.
3
Thread the new switch in by hand on the sealed pipe threads, then tighten snugly with the correct wrench on the body hex — do not over-torque or crush the insulator.
4
Reconnect the warning wire under the 10-32 stud nut with the lock washer in place. Reconnect the battery, start the engine, and confirm the alarm clears as oil pressure builds and that there are no oil leaks at the port.
If you are unsure about warning-system wiring or oil-gallery location, have a marine technician complete the install.
Troubleshooting & FAQ
Why Choose JLM MARINE?
- Precision Fit: Thread and terminal layout matched to MerCruiser 87-805605A1 low oil pressure switch applications.
- Quality Control: Each batch is inspected for dimensional consistency and workmanship.
- Direct from Manufacturer: Aftermarket marine parts engineered for reliable warning-system service.
We can ship to virtually any address in the world with free shipping available for most regions.
For our typical US and Canadian customers , our shipping timeframes are as follows:
- Amazon FBA: orders will be delivered within 1-5 business days after placing the order (during certain special periods such as major promotions, Christmas, etc., the delivery time of Amazon FBA may be affected).
- US warehouse shipment: orders will be delivered within 5 days after placing the order.
- China warehouse shipment: orders will be delivered about 12 days after placing the order.
When you place an order, we will estimate shipping and delivery dates for you based on the availability of your items and the shipping options you choose. Depending on the shipping provider you choose, shipping date estimates may appear on the shipping quotes page.
Please also note that the shipping rates for many items we sell are weight-based. The weight of any such item can be found on its detail page. To reflect the policies of the shipping companies we use, all weights will be rounded up to the next full pound.
Founded in 2002, JLM Marine has established itself as a dedicated manufacturer of high-quality marine parts, based in China. Our commitment to excellence in manufacturing has earned us the trust of top marine brands globally.
As a direct supplier, we bypass intermediaries, which allows us to offer competitive prices without compromising on quality. This approach not only supports cost-efficiency but also ensures that our customers receive the best value directly from the source.
We are excited to expand our reach through retail channels, bringing our expertise and commitment to quality directly to boat owners and enthusiasts worldwide.
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