donaldb Posted January 18, 2019 Share Posted January 18, 2019 There is a silver metal housed relay behind the brake booster that has started buzzing. I looked through the wiring diagram but have not been able to find it. Anyone know what the relay controls? While we're at it, what is the black one control also. Thanks Link to comment Share on other sites More sharing options...
grumpin Posted January 19, 2019 Share Posted January 19, 2019 I don't think you have in tank electric pumps, so I would guess the Trailer Lamp Relay. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 19, 2019 Share Posted January 19, 2019 I don't think you have in tank electric pumps, so I would guess the Trailer Lamp Relay. The trailer light relay shows in an illustration here: http://www.garysgaragemahal.com/trailer-option1.html. Big Blue has the aux battery solenoid, which is the shiny unit in the pic below, as well as the fuel pump relay and the trailer lighting relay, shown to the right of the aux battery solenoid. Link to comment Share on other sites More sharing options...
Steve83 Posted January 19, 2019 Share Posted January 19, 2019 Anyone know what the relay controls?For all electrical devices, ID them by their wire colors. Post pics. The most-important wire (for ID) on a relay is the little one that triggers it to change state (on/off) since that identifies its function. Link to comment Share on other sites More sharing options...
Rembrant Posted January 19, 2019 Share Posted January 19, 2019 There is a silver metal housed relay behind the brake booster that has started buzzing. Behind the brake booster, do you mean on the firewall inside the cab? What is the shape of the relay? Link to comment Share on other sites More sharing options...
donaldb Posted January 20, 2019 Author Share Posted January 20, 2019 Pictures added Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 20, 2019 Share Posted January 20, 2019 Pictures added I suspect the black one is the trailer lights relay. But don't know what the silver one is. We need to know what the wire and connector colors are going to both of those relays. And each wire should have a solid color and a secondary color, but you may have to uncover the wire from in a covering to be able to tell the colors. Link to comment Share on other sites More sharing options...
Rembrant Posted January 20, 2019 Share Posted January 20, 2019 I suspect the black one is the trailer lights relay. But don't know what the silver one is. We need to know what the wire and connector colors are going to both of those relays. And each wire should have a solid color and a secondary color, but you may have to uncover the wire from in a covering to be able to tell the colors. My 1984 FSM only shows two possible relays in that location. Trailer Lights Relay: Or the Marker Lights Relay, which was supposedly only on the DRW trucks: However, that's from my '84 FSM...could be different stuff included in 1985 for sure. Snagged this picture below from FTE, also from a 1985, and it was clicking, but the guy was trying to diagnose a no start issue, and the clicking silver relay was never identified. That's my 2 cents while finishing my morning coffee. Not much help, I know. Link to comment Share on other sites More sharing options...
85lebaront2 Posted January 20, 2019 Share Posted January 20, 2019 I suspect the black one is the trailer lights relay. But don't know what the silver one is. We need to know what the wire and connector colors are going to both of those relays. And each wire should have a solid color and a secondary color, but you may have to uncover the wire from in a covering to be able to tell the colors. My 1984 FSM only shows two possible relays in that location. Trailer Lights Relay: Or the Marker Lights Relay, which was supposedly only on the DRW trucks: However, that's from my '84 FSM...could be different stuff included in 1985 for sure. Snagged this picture below from FTE, also from a 1985, and it was clicking, but the guy was trying to diagnose a no start issue, and the clicking silver relay was never identified. That's my 2 cents while finishing my morning coffee. Not much help, I know. He hasn't said what engine he has so could it be the choke relay for a 351 4V engine? the 1986 EVTM shows a group of relays in the 5.8L 4V carburetor circuits but isn't clear on their locations. Link to comment Share on other sites More sharing options...
Gary Lewis Posted January 20, 2019 Share Posted January 20, 2019 He hasn't said what engine he has so could it be the choke relay for a 351 4V engine? the 1986 EVTM shows a group of relays in the 5.8L 4V carburetor circuits but isn't clear on their locations. I had wondered that as well, but there appears to clearly be a black/yellow wire in the pic and I can't find it in any of the EVTM illustrations I've looked at. Here's the carb ones: Link to comment Share on other sites More sharing options...
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