544 Intermittent Wiper (after 6-12V Conversion) Notes
by SW-EM Guest Contributor Richard Allen [Comments, graphics and links added, Ron] 

First Published Mar 2022  

12V to 6V Converter

Reference Information
    Bosch 0-336-920-004


Acknowledgement and Foreword:  Thanks to Rich Allen for developing, compiling and contributing this information.  Rich is clearly a electrically qualified individual, who has the skills to engineer the many details of combining the voltage converter and intermittent control modules to the Wiper Motor Assembly (with Dynamic Braking), to meet the functional requirements such a somewhat complicated system.  [Reference:  In this thread on the Volvoniacs (German) Forum, where the owner tried to do the same thing, they didn't get it right, the voltage converter burned up, and possibly also the Wiper Motor, after the failed voltage converter applied a full 12V to the 6V rated motor.]

I would not recommend trying to reproduce his successful results of this project to anyone not (at least!) highly skilled and experienced in automotive electrics! 
I would therefore call this an Expert Level Project rated at out of 5 Wrenches!    

The information is included here in good faith to help other owners of vintage Volvos.  It is substantially correct to Rich's and my knowledge, but must be used in conjunction with safe, electrical engineering and automotive shop practices.  The user is strictly responsible for its use and implementation. Ron

Feedback from the reader's results are invited.  Rich has given his OK to post his contact info here, and said that he would answer questions if you ask nicely!  Contact him at:  rich AT rich-allen DOT net


Intermittent Wiper Switch and Voltage Control on PV544
Rich Allen, 5/2018

I have a 1960 Volvo Pv544 with a one speed wiper motor [the only kind available from the factory!]. The washer switch is separate. The car was converted from 6 v to 12 v and had a 1.2-ohm resistor installed in the power line. The problem is the wipers still ran uncontrollably fast.  [That Dropping Resistance does seem to be a bit low...experience shows it should have been more along the lines of 6.0Ohms.  Ref:  https://www.sw-em.com/Vintage_Volvo_6V_to12V_conversion.htm#Dropping_Resistors ]

Reducing the motor speed.
Rather than install more static resistors I replaced the existing resistor with an Aideepen 300W 20A adjustable output Buck converter that I purchased on Amazon for $14. I over-specified the wattage, but it was cheap and relatively small so figured it would generate little heat. 

First, I calibrated it by connecting the input terminals of the converter to the car battery and adjusting the voltage adjustment screw until the output read half of the battery voltage. On this unit, there is an amperage adjustment - which I did not adjust. To connect the unit to the wiper switch, I grounded the (minus) terminals of the unit to the chassis then connected the input + terminal to the power wire and the output + terminal to the switch 54 terminal wire. The unit gave the correct wiper speed without further voltage or amperage adjustment.

Unlike before, there was little difference in wiper speed whether the windshield was wet or dry.  This is not unexpected, and can be explained by the output voltage of the (smarter) converter (with internal Voltage Reference) not changing as a function of load current, as it does in the simpler (dumb, but arguably more reliable) Dropping Resistor implementation.  This change in voltage results in a change in wiper speed. 

Adding the Bosch 0-336-920-004 Intermittent Wiper Switch.

I found that a few internet sites are now offering this $100 unit for about $50. Initially, I was confused because I thought this unit could simply replace the existing wiper switch. Unfortunately, there is no non-intermittent pass-through position on the switch. Had I installed this in place of the regular switch, there would still be an intermittent lag on the fastest speed. Instructions for Volvos do come with this unit, but not for my dynamic braking, one-speed motor. To gang this intermittent switch with the original wiper switch I made 3 Male Female Female (MFF) “Y” connectors as picture and one FF connector of equal length. 


The wiring took a while to figure out, but below is a table of the connections: 

I installed the intermittent switch on the bottom of the dash, right in front of the radiator shade pull. There was space for this bulky switch and it was close to the original wiper switch. So far it works great but I need to track durability of the Buck Converter.

Here is Rich's wiring diagram sketch [Unchecked in detail by me, but at a cursory glance, it looks OK!]

Rich also advises that the power was taken from the main Ign power circuit with no Fuse rating increase from the standard 25A.

End of Rich's documentation.


Reference Information [...not part of Rich's original Documentation and added by me.]:

Bosch 0-336-920-004




Thanks to Erwin F. of the Volvoniacs Forum for providing the Bosch 0-336-920-004 Switch Installation Instructions, which I have trimmed to show only the Volvo relevant parts.  Notice that the Switch is suitable for both simple Field Motor (Wiring 2) and Wiper Motor with Dynamic Braking (Wiring 1) configurations.  I have added where the 122 would be categorized...for some reason, it was not included in the Bosch documentation... 

Bosch 0-336-920-004 Switch Installation Instructions Excerpt for Volvos. 


This article is a guest contribution to the SW-EM site by Richard Allen, and Copyright © 2022.  The terms Volvo, Bosch, and Aideepen are used for reference only.  Neither Rich nor I have no affiliation with any of these companies other than to keep their products working for us, help other enthusiasts do the same, and in my case, also present my highly opinionated results of the use of their products here.  The information presented comes from Rich's and my experience and carefully considered opinion, and can be used (or not!), or ridiculed and laughed at, or worshipped, at the readers discretion.  As with any recipe, your results may vary, and you are, and will always be, in charge of your own knuckles, and future! 

You are welcome to use the information here in good health, and for your own non-commercial purposes, but if you reprint or otherwise republish this article, you must give credit to the author or link back to the Rich and the SwEm site as the source.  If you don’t, you’re just a lazy, scum sucking plagiarist, and the Boston Globe wants you!  As always, if you can supply corrections, or additional objective information or experience, I will always consider it, and consider working it into the next revision of this article...along with likely the unique metaphor and probably (likely) wise-a** comment. 


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