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-   -   Can someone please explain to me what the start bridge relay does? (https://rennlist.com/forums/928-forum/731073-can-someone-please-explain-to-me-what-the-start-bridge-relay-does.html)

ledee416 12-11-2012 02:53 PM

Can someone please explain to me what the start bridge relay does?
 
I noticed that they are differently listed for mt and at. what is he deal exactly?

I have been jumping this relay (was like it when I got the car), and was told by PO it was the fuel pump relay in my 1980 US. After having to jump the pump relay in my Euro, I realized that it was not in fact the pump relay, but rather the start bridge. I was just curious as to what it did exactly, and if someone has the numbers off of it so I can find a new one. It doesnt appear as if either ebay or 928 site stocks it by name.

Ducman82 12-11-2012 03:02 PM

the bridge by passes where a relay would be. that relay is so the car will only crank in neutral or park

dr bob 12-11-2012 03:03 PM

The starter relay is used in the automatic cars to allow a neutral safety switch to limit starting to when the selector is in either park or neutral position. In manual transmission cars, with no such safety switch, the jumper is installed between 30 and 87, so that the key switch can directly actuate the starter solenoid.

[fixed terminal numbers per Alan's info below. Thanks!)

Alan 12-11-2012 03:25 PM

Its a standard 87/30 bridge - in this case the relay 30 terminal is actually fed by the starter switch (50)

When there is a relay (AT) - 86 is ignition and 85 goes to the neutral safety switch (relay on when in neutral & ignition on). This config changes in later years so the relay actually decoupled the switching from the switch.

Alan

ledee416 12-11-2012 03:33 PM

as of right now, I have it jumped between 87 and 30. There is no bridge on it, just a wire with flat blade connectors. Do I need to put an actual bridge on there, or can I keep it the way it is? I am wondering if this setup will drain my battery. If it isnt a relay, then I am guessing it wont, but I am not sure.

Alan 12-11-2012 03:39 PM

1 Attachment(s)
A relay bridge looks like this...

Alan

James Bailey 12-11-2012 03:53 PM

bridging or a jumper wire means your car WILL start in gear which can be a big surprise !!!! Not what people expect with an automatic. Be safe you never know who might be starting the car.

Alan 12-11-2012 03:56 PM

Bridge as shown is 928.615.125.00 (for MT)

As Jim said if this is in fact an AT car fix this with a standard Bosch SPST/SPDT relay (any auto store) and whatever else may be needed to fix the neutral safety switch (if needed?)

Alan

ledee416 12-11-2012 04:23 PM

awesome. thanks. It was weird. I was trying to pull the same relay out of my euro. It had no cover on it, and when I squeezed it to pull it out, the car turned over. it was pretty startling. I guess I will go hunting for the standard relay then. just ask for Bosch SPST/SPDT relay?

Alan 12-11-2012 04:41 PM

Either one works just fine: Bosch style SPST or Bosch style SPDT - can be any actual brand.

Note - Always disconnect the battery before doing electrical work on your 928...

Alan

dr bob 12-11-2012 06:14 PM


Originally Posted by ledee416 (Post 10064770)
awesome. thanks. It was weird. I was trying to pull the same relay out of my euro. It had no cover on it, and when I squeezed it to pull it out, the car turned over. it was pretty startling. I guess I will go hunting for the standard relay then. just ask for Bosch SPST/SPDT relay?

^^^^ What Alan said about disconnecting the battery.

The relays seem to be pretty secure in their sockets. It's easy to squeeze a relay cover hard enough to actuate the relay inside, or pull on it hard enough to separate the cover from the base. There's a fancy relay pliers that solves the first problem but still rsisk pulling the cover off. There are more than a couple solutions as always. Mine uses a couple paint can openers with the ends bent over to almost 90. High-dollar Home Depot tools that have what looks like a bent screwdriver end and a looped handle. I just added to the bend so it could fit under the base of the relay. Slide them under on opposite sides, rock a little then pull, and the relay will be out on the carpet in a flash. To avoid that flash, follow Alan's suggestion about disconnecting the battery first, so the metal puller ends don't short the relay pins together.

jbrob007 12-11-2012 07:31 PM

The cool thing about the Home Depot paint can openers flattened out to remove relays is the OTHER end is a bottle opener... perfect for opening that expensive bottle of German beer when the job is done! :)

17prospective buyer 12-11-2012 08:03 PM

So manuals don't even have a clutch switch? That would explain why i can start my 928 without pushing the clutch in. Good to know it's not a PO butcher job.

jbrob007 12-11-2012 08:10 PM

My 86.5 has a clutch switch... What it does exactly I'm not sure. I assume it has something to do with starting the car like blocking out the ignition while in gear. But there is a contact switch activated by the clutch pedal arm when depressed... at least on my car.

Hilton 12-11-2012 08:39 PM


Originally Posted by jbrob007 (Post 10065317)
My 86.5 has a clutch switch... What it does exactly I'm not sure. I assume it has something to do with starting the car like blocking out the ignition while in gear. But there is a contact switch activated by the clutch pedal arm when depressed... at least on my car.

The pressure switch on the clutch pedal is for the cruise control - so you can change gear while cruise is active and the engine won't redline :)


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