{"id":1111,"date":"2026-07-03T11:03:20","date_gmt":"2026-07-03T16:03:20","guid":{"rendered":"https:\/\/gtyurkon.com\/MC850\/?p=1111"},"modified":"2026-07-03T11:03:25","modified_gmt":"2026-07-03T16:03:25","slug":"oil-pump-monitor-and-headlight-relays","status":"publish","type":"post","link":"https:\/\/gtyurkon.com\/MC850\/2026\/07\/03\/oil-pump-monitor-and-headlight-relays\/","title":{"rendered":"Oil Pump Monitor and Headlight Relays"},"content":{"rendered":"

About this Post<\/strong><\/p>\n

I had been wondering for some time what I would do about a non-functional oil pump monitor, the one on the left in Figure 1. Working or rebuilt units seem unobtainable, and I didn’t have any confidence in the bimetallic strip design anyway. I was hoping for something better. Then, the newest issue of Vintage Views magazine arrived (Vintage News, Vintage Saab Club of North America, Volume 22 Number 1, Spring 2026). On page 32, I found a two-page article by Paul Bates who had a similar problem and found a solution. He had a friend named Rick who was a bit of a techno-nerd willing to help. Rick was gracious enough to share his excellent solution. Click this hackster.io link<\/a> to see all the details he shared, including a schematic and, most importantly, the Arduino code (sketch) to implement his design.<\/p>\n

\"1.<\/a>

1. Sorry State of Original Relays<\/p><\/div>\n

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I left a complimentary comment for Rick on hackster, and Rick replied with an offer to sell me a left over assembly that he had no further need for. I agreed to purchase it and received an assembly like that shown in Figure 2. However, looking at the size of the relay and the buck voltage regulator, I was amazed that they were able to fit that in the small SAAB oil monitor box. I, therefore, started searching for an equivalent, normally closed, solid state relay, hoping to find an equivalent, but smaller, relay. After discovering the IXYS CPC1705Y solid state relay, I decided to attempt making a small PCB using Rick’s design with the solid state relay. I also decided to replace the buck converter with an old-style linear voltage regulator to save space. The remainder of this post describes this little adventure.<\/p>\n

Before continuing, however, I want to make it clear that I take no credit for anything. I merely made modifications to Rick’s excellent design to save space. Rick Gessner deserves all the credit for this, especially because of his willingness to freely share his work. And, with that spirit of sharing in mind, I have made files that I created or modified available at this link on Google Drive: My PCB Design Files<\/a>. Who knows, somebody familiar with Kicad might find the Kicad schematic useful for designing a more professional looking PCB. The PCB copper image might be useful to someone wanting to make their own board using toner transfer or other methods. However, at age 83 as I write this, these files may not be around for long, so grab them while they are there if you are interested.<\/p>\n

\"2.<\/a>

2. Arduino System in Vintage Views Magazine<\/p><\/div>\n

Designing the Solid State Oil Monitor PCB<\/strong><\/p>\n

The first step in designing the PCB was to find a way of squeezing all of the components into the smallest possible space. The components also had to be arranged so that they could be connected by copper PCB traces without the traces overlapping each other. I did this work with a multi-layer GIMP image file as shown in Figure 3, with all 17 or so layers made visible. Figure 4 shows only the copper layer. It is this image which I used for doing a toner transfer to a PCB board before etching the board. The board is precisely 1.7 inches by 1.3 inches. This image SHOULD NOT be mirrored before printing — print it as shown, but sized correctly.<\/p>\n

\"3.<\/a>

3. My GIMP PCB Layout for Solid State Version<\/p><\/div>\n

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\"4.<\/a>

4. Black and White Copper Layout for PCB Toner Transfer<\/p><\/div>\n

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The Kicad schematic is shown in Figure 5. Please take note that this is essentially the same as Rick’s schematic, but slightly modified for the solid state relay and the linear voltage regulator. I used pins D8 and D10 on the Arduino in place of D12 and D2 to make it easier to design copper traces on a PCB. This Kicad schematic might be useful for anyone wishing to generate a Kicad PCB. Also take note that the LM317BTG was chosen for it’s operating temperature range. Make sure to use an LM317 capable down to minus 40 degrees. Most only work down to freezing, or 32 degrees Fahrenheit.<\/p>\n

\"5.<\/a>

5. Kicad Schematic for Solid State System<\/p><\/div>\n

Construction and Testing of Oil Pump Monitor<\/strong><\/p>\n

I definitely didn’t get things right the first time, or the second, and so on. To start with, I removed the Arduino from Rick’s prototype but with some damage due to carelessness, but it was still usable. I built a first prototype on perf board, and even a second with an Arduino Nano Every. They worked but were too large and really tough to make. I then turned to GIMP and designed a PCB board similar to that of Figure 4 above. On this, I installed Rick’s damaged Arduino Nano which had a broken Vin pin and one broken GND pin, using the +5V pin and the alternate GND pin. This board tested very well but I was unhappy with the thickness and the difficulty of construction. I refer to this as version 1. The version 1 PCB is shown in Figure 6 beside the remnants of Rick’s prototype.<\/p>\n

\"6.<\/a>

6. Original (Minus Arduino) vs 1st PCB Prototype<\/p><\/div>\n

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For the next two PCBs, which I refer to as version 2, I redesigned the PCB and installed an Arduino Nano Every on each. The Every model is good for this application because it has no bottom-side components and can be installed flat on the PCB. These both tested well, and the test setup is shown in Figure 7. Please note that the above-illustrated schematic and PCB board layouts are for a version 3 which I haven’t actually made yet. But I am sure it will work. However, the arduino code (sketch) required changes. The modified sketch is available at the Google Drive link I provided elsewhere in this post.<\/p>\n

\"7.<\/a>

7. Bench Testing a Prototype<\/p><\/div>\n

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I turned my attention now to the firewall case to make space for the PCBs. Figures 8 and 9 illustrate the cutting process and result. As you might notice in Figure 8, I used a Dremel. My favorite tools were a diamond-coated cutting blade, a small nibbler as seen in the Dremel, and a longer side cutting tool for smoothing some surfaces. Figure 9 shows that one of the ugly perf board assemblies would have fit.<\/p>\n

\"8.<\/a>

8. Cutting the Case with a Rotary Tool<\/p><\/div>\n

\"9.<\/a>

9. Carved-Out Case beside a Perf-Board Prototype<\/p><\/div>\n

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Figure 10 shows a pair of version 2 PCBs after a conformal coating has been applied for waterproofing. I protected the USB port and the reset button so they will remain available for future software updates if needed. Also, I cut and cleaned the coating off of the LM317 heat sink which I shouldn’t have coated to begin with. However, heat is not a problem as the Arduino only drew from 37 mA to 42mA during operation, and I couldn’t feel any noticeable heat on the LM317. Figure 11 shows one of the PCBs being glued to the case with some E6000 glue. Turns out it doesn’t cling to the conformal coating but it made a nice, soft fitted base for the PCB to rest on. Consequently,as shown in Figure 12, I strapped the PCB to the case with insulated wire. I removed some soft silicone insulation from 16 ga wire and slipped it over the 20 ga wrapping wire to act as a cushion. Figure 13 shows the opposite side (front) of the case. Figure 14 shows the terminal wires soldered to the spades, and Figure 15 shows the back side of the assembled case.<\/p>\n

\"10.<\/a>

10. Version 2 PCBs with Conformal Coatings<\/p><\/div>\n

\"11.<\/a>

11. Version 2 PCB Being Glued to Case<\/p><\/div>\n

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\"12.<\/a>

12. Back View of Ver. 2 PCB Strapped to Case<\/p><\/div>\n

\"13.<\/a>

13. Front View of Ver. 2 PCB Strapped to Case<\/p><\/div>\n

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\"14.<\/a>

14. Ver. 2 PCB Soldered to Terminals<\/p><\/div>\n

\"15.<\/a>

15. Back Side of Assembled Oil Pump Monitor<\/p><\/div>\n

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And, at long last, Figure 16 shows the completed and working (hopefully) oil monitor relay!!!<\/p>\n

\"16.<\/a>

16. Front View of Assembled Oil Pump Monitor<\/p><\/div>\n

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Replacement and Rewiring for Euro-Style Headlight Relays<\/strong><\/p>\n

I have fond memories of the floor-mounted headlight dimmer I got so used to in all the cars I drove in the 1960’s, including my fist SAAB 96 in 1967. I also have not-so-fond memories of my left foot being on the clutch at the moment I needed to dim the headlights. Being that the headlight relays in my 66 MC850 are toast, I have decided to convert to the euro-style dimmer on the turn signal stalk. This turns out to be rather easy because the USA SAABs had the same turn signal stalk as the European SAABs. They just weren’t wired, but a different relay was used. It seems, however, that good replacement, euro-style relays are hard to find but I found a good solution. The early C900 SAABs had a single relay box which contained two relays, functionally identical to the two relays on the European MC850s. And, these were readilly available on eBay.
\nFigure 17 shows my first eBay purchase. Not so good. Figure 18 shows my second eBay purchase. Very good.
\nFigure 19 shows the cleaned-up C900 relay with a homemade mounting tab added. It should look good on the firewall and give me the euro-style headlight dimmer. I hope.<\/p>\n

\"17.<\/a>

17. Rusty Early C900 Headlight Relay<\/p><\/div>\n

\"18.<\/a>

18. A Good Quality Early C900 Headlight Relay<\/p><\/div>\n

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\"19.<\/a>

19. C900 Headlight Relay with Riveted Mount<\/p><\/div>\n","protected":false},"excerpt":{"rendered":"

About this Post I had been wondering for some time what I would do about a non-functional oil pump monitor, the one on the left in Figure 1. Working or rebuilt units seem unobtainable, and I didn’t have any confidence in the bimetallic strip design anyway. I was hoping for something better. Then, the newest […]<\/p>\n","protected":false},"author":1,"featured_media":1113,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_s2mail":"","footnotes":""},"categories":[1],"tags":[],"class_list":{"0":"post-1111","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-uncategorized","8":"czr-hentry"},"_links":{"self":[{"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/posts\/1111","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/comments?post=1111"}],"version-history":[{"count":35,"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/posts\/1111\/revisions"}],"predecessor-version":[{"id":1165,"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/posts\/1111\/revisions\/1165"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/media\/1113"}],"wp:attachment":[{"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/media?parent=1111"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/categories?post=1111"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/gtyurkon.com\/MC850\/wp-json\/wp\/v2\/tags?post=1111"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}