I'm in the process of wiring the overdrive in my 1949 Stude pickup. Original 6 volt positive ground system. Can I use a 12 volt relay instead of a 6 volt?
The 6 volt supply mightn't be enough to energise the relay coil. If it does it might be marginal. Relay coils have what's called Hysteresis. This means a 12 volt relay might cut in when you apply say, 10+ volts to the coil, but won't drop out till the coil voltage drops to below say 6 volts. I'm just using these numbers as examples, results may vary.Have you tried it on the bench?
Could be you could get a 5V relay at Radio Shack (they will stand up to 7 or 8 volts without harm if momentary use..... If your generator puts out more or for continuous duty, you could use a zener diode to regulate voltage back to 5V.
they make a 6vdc bosch relay. It will work with positive ground just fine, still 30A I think. I tried the 12v on a 6v first, it was hit/miss on it working.
Replacement 6 volt relays are available but pricey... $100. I would like to try the bench testing but I am a novice. Are you suggesting wiring the relay in place and reading the the output?
I have a Ford overdrive, which is a similar (if not exactly the same) Borg-Warner unit. The overdrive relay is triggered by bringing it to ground and not the hot lead. It's triggered by the governor unit on the ****** tailshaft when the car hits 26-28 mph and the contacts close, bringing it to ground. Most relays that you can buy are triggered by bringing the hot lead to the trigger. You need a relay triggered by ground that is rated for continuous duty like a headlight relay. I tried a horn relay once and it got too hot to touch in 10 seconds. As for the voltage, you may have problems if the 6 volts isn't enough to throw the relay. You can get a new relay at www.shoeboxford.com, or you can skip the relay and wire the unit to a toggle switch for manual control.
You can also buy 6volt replacement relays for kids motorized toy cars for much cheaper ( 5-15 bux) and they do exactly the same thing. FYI.
Long time reader, new poster. I just wanted to point out a couple general facts about relays, specifically bosch relays. A relay is simply an electromagnetic switch, and unless it's a special relay that contains a diode, it has no polarity. Pins 85 and 86 are the coil, and it doesn't matter if you use a negative (ground) or positive (batt) trigger. Just wire the other terminal to the opposite polarity. In mike51merc's setup, all you would need to do is supply battery voltage to one of the two pins and connect the other to the tailshaft mounted trigger. Then, connect battery voltage to the input pin 87 with a sufficiently large gauge wire. You can even use this circuit to supply power to the coil side of the relay with a short jumper. Last, connect the output pin 30 to your overdrive solenoid. A high amperage continuous duty relay is about 3x more expensive than a standard one, but that still puts it below $30. Such a relay can be seen here, as long as the link continues to work: http://www.fifthaveinternetgarage.com/parts/parts_counter_2.html Also, Bosch relays are now made by Tyco, and the 12v automotive relay has a pull in voltage of about 8v, and a drop out voltage of between 1-5v depending on whether it has an internal suppression resistor (which is not always specified). These relays will not work in a 6v system. This comment is meant to be helpful. If it's confusing or I'm wrong, I'm sorry
We recently had trouble with a Bosch relay not coming in, just making a "buzzing" noise. Found bat voltage was only about 10 V, another full voltage bat brought it in just fine. Good tech info on that fifthaveinternetgarage link for quick trouble shooting on a variety of subjects, well written so even dummy me could understand it. Thanks for posting. Ed
Some of those relays were identical to horn relays...... 12 as well as 6 volt...... Glad you found one that fixed the problem... Happy Roddin' 4TTRUK
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