Pagoda SL Group
W113 Pagoda SL Group => Electrical and Instruments => Topic started by: alpina on February 26, 2015, 22:50:26
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Following on from a problem blowing fuse 6 when the ignition switch is in the start position. I have now discovered that if I pull the connector off
The 4th relay the fuse no longer blows.
Car starts and runs fine, (did even when the fuse blew) every thing else seems to work fine. So what is this 4th relay for? Is it okay to leave disconnected? And why would it blow the fuse once connected?
I have 4 relays near the brake booster from back to front: 1)wiper 2)FIP solenoid 3)CSV solenoid. The 4th relay is at 90 degrees to the other on an L shaped bracket. The electric socket is plugged piggyback-style into the socket of the CSV relay. The 4th relay is of the same shape and size as the FIP & CSV relays.
I know there has been talk about this 4th relay in the past, but it still seems a mystery.
Thanks
DM
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Did a bit of a search (the search function is your friend) and found this
http://www.sl113.org/forums/index.php?topic=8896.0, see if that helps.
I just used "relay" in the search line, and limited the search to the topic line only, I got three pages of hits, and this was the last entry! (I had some seat time here at LAX before heading home)
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I think the fourth relay may have to do with the de-celleration solenoid. I will try to verify this as fact later.
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Thanks Jonny B,
The search was my first port of call. i spent a few hours searching many threads. I have also been in contact with Andy who started the thread
you found. And even now years down the line he has not found a difinative answer.
If i unplug the connector to the 4th relay the fuse no longer blows. The car starts and runs okay with the 4th relay disconnected. but i would like to
narrow the problem down, before speaking to an auto electrician.
best regards
Darren
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Darren,
Here's what we know so far, which isn't much (http://www.sl113.org/forums/index.php?topic=8896.0) :
1. this relay is not not an owner add-on; it was standard issue for some 280SLs
2. It energizes the fuel pump when pin 87 of this relay is powered.
Joe (JA17) thinks that it may be related to the deceleration solenoid. This could make sense if MB intended to shut off not only the fuel supply to the fuel injection pump (with the solenoid), but shut off the fuel pump as well during deceleration.
Many of us with a deceleration solenoid on our FIPs have disconnected the wire to this solenoid.
If Joe is correct, perhaps you have a short at that wire.
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Here is the scoop on the #4 relay. I had the information in my notes. If your car is one of the later USA emission versions that has the decelleration solenoid (lower one of two on the injection pump), then it was equipped with this fourth relay, along with the large RPM relay over by the coil. The car should also have a micro switch mounted on the firewall. There is a separate wiring harness which is added to the car to run all these devices. This add-on wiring harness is a bit complex but one end ties into the neutral safety switch on the firewall and meanders to that fourth relay which is a five prong relay instead of a four prong (as is the other three). After leaving the neutral safety switch on the firewall two wires (green/black) and (green/white) branch-off and connect to the micro switch on the firewall. Next a wire from inside the car is feed into this harness (I suspect that this is the wire coming from the fuse box). Next along the way a brown ground wire emerges and is attached to the ground lug on the relay brackets with the some other grounds. Next a four-wire bundle branches-off and plugs into the large deceleration relay (near the coil). The four wires here are brown, black, black/red, green/blk. Next down the harness a green/black single wire branches off and connects to the ignition coil. Another single wire branches off next and connects to the fuel shut-off solenoid on the injection pump. Lastly a six terminal plug attaches to the bottom of that #4 fourth relay. The fourth relay is a five prong relay as mentioned and two sockets of the six prong plug are empty. Other wire colors in this plug are black/red, green, green/red, and black. So that's as much as I know on the #4 relay. Hope this helps. I suspect that the short circuit in your system might be the lower solenoid on the injection pump. You may consider simply just disconnecting it as is done without consequence on many cars.
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I've added this to the bottom of this page… http://www.sl113.org/wiki/Electrical/EmissionControlSystem
Now someone draw a diagram!
Peter
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Thanks, well done Peter!