Wednesday, November 29, 2006

VW - The By-Pass Solenoid Trick

St. Muir and the By-Pass Solenoid, or "Soul y noid? We don' need no stee-king solenoid!"

This one really gets me hot under the collar, first because it ain't a by-pass-anything, and second because the usual method, using an old Ford starter solenoid a la St. Muir is dumber than hell, partly because it ain't a solenoid at all but a contactor, and finally because you just don't need a starter contactor for this particular job.

The problem is that Volkswagen feeds their starter solenoid 12vdc by way of China. They run the juice all the way up to the front of the vehicle, through the starter switch which isn't all that reliable to begin with, then all the way back to the solenoid -- which is where the juice started its journey to begin with.

By the time those 12 volts have marched up front, squeezed through the switch terminals and hiked all the way back to the solenoid about of half of them are dead and the others have blisters. They jump inside the solenoid, put their electronic shoulders to the wheel but find they're played out by the trip. If the solenoid moves at all it does so sluggishly, often not strongly enough to close the contactor terminals that provide juice to the starter motor.

The fix is to keep those 12 volts from wasting their time and energy on that useless hike by putting in a relay. That's what that Ford contactor is pretending to be. The joke is, the contactor uses almost as much juice as the VW solenoid! A wiser choice is a headlight or horn relay. Cheap, easy to find and easy to mount. Screw it to the fender well inside the engine compartment to help keep the terminals clean.

What the relay does is tell those 12 volts when to go to work on the solenoid. You wire your relay with the same wire originally used for the VW starter solenoid but you install new, heavier wires -- with a shorter run to the battery and solenoid -- from your relay. Since a headlight relay only needs an itty-bitty amount of power to pick or transfer, the original wiring provides more than enough energy despite its long run. And since your new, heavier wiring provides a shorter, neater, cleaner, prettier, healthier and politically more correct run between the battery and the VW starter solenoid, it fires right up every time.

This isn't a new problem. In fact, Volkswagen came out with a fix for it years ago. Their solution? A simply relay packaged as a completely wired kit, including instructions. The part number was something like VK-1 and you could buy it from any dealer for about two bucks.

I understand Gene Berg started selling Ford contactors because he got tired of trying to explain to St. Muir deciples that St. John didn't know very much about elektrissity. I know a whole bunch about elektrissity and I'm still alive, even though I use a headlight relay to pick my solenoid and a horn relay to turn on my back-up light and an itty-bitty microampere relay out of a short-wave radio to tell my external cooling fan when to turn on, although a Ford contactor would have done the job -- sorta -- in each and every case and would have, if St. Muir had thought of back-up lights and cooling fans. ("Back-up lights! We don' need no steeeking back-up lights!")


Cold weather brings home the problem of the voltage drop in the long wiring runs common to a Volkswagen bus. If you want reliable starts and brighter headlights you need to know more about heavier gauge main buss wiring and the use of relays. You are the mechanic-in-charge of your vehicle. Sometimes that calls for you to be an electrician as well.


Ed. Note: I've heard Gene Berg Ent. now offers the original VW relay instead of a Ford contactor. Check their catalog.

1 comment:

Anonymous said...

Just FYI, the current Bosch part number for the hot start relay kit is "WR-1".