Aftermarket underhood junction block
Thread Starter
TECH Apprentice
Joined: Nov 2008
Posts: 322
Likes: 30
From: Arizona
Aftermarket underhood junction block I have a truck build (a 2001 Tahoe) too many upgrades to list. One of the upgrades is a AEM 50-1200 340LPH fuel pump. I suspect my fuse block maybe acting up. I rewired from fuse block connector to pump with 12 gauge wire. The circuit for pump from factory is 20 amp fuse... AEM told me 15 amps should be good (I left 20 amp). I developed a loss in pressure. Pump went from 57 PSI reference to 52 PSI reference and sometimes looses pressure all together. I'm getting a new pump but suspect issue could possibly have been wiring / trace in my 24 year old junction block. I could take the junction block apart and increase size of the trace... However, I think I'd like to use the factory relay to switch another relay with a larger connection to the battery, instead of powering the pump directly off the factory pump relay... Possibly a relay in a high quality aftermarket junction block or just a stand along relay fuse combo.
Anybody have any suggestions?
Anybody have any suggestions?
You don't necessarily need to use the factory Relay just use the 12v wire from the PCM that energizes that Relay and install a bigger Relay with bigger wiring if you think that's the issue. The truck Fuse Block is some intergrated design, everything is metal traces molded into the plastic, I don't like working with them.
Here's how I'd do it, I've done similar.
12v Trigger Wire from the PCM is in RED Connector Pin 9, goes to Pin 86 on the Relay
Ground Pin 85 on the Relay
12v Battery to Pin 30 on the Relay, 12ga wire. 20A inline Fuse in it somewhere between the Battery and Relay.
12ga wire from Pin 87 on the Relay to the Fuel Pump
12ga wire grounding the Fuel Pump to a good spot on the Frame
Running the 12ga to the Fuel Pump takes a little time but if you already have done it then it's there. Install that wiring tuck it up mount the Relay near the factory Fuse Box so the wire from the PCM can reach it, have to take it apart to find that wire on PCM RED 9. Clip it at whatever Connector it's in and run it to the new Relay.
Here's how I'd do it, I've done similar.
12v Trigger Wire from the PCM is in RED Connector Pin 9, goes to Pin 86 on the Relay
Ground Pin 85 on the Relay
12v Battery to Pin 30 on the Relay, 12ga wire. 20A inline Fuse in it somewhere between the Battery and Relay.
12ga wire from Pin 87 on the Relay to the Fuel Pump
12ga wire grounding the Fuel Pump to a good spot on the Frame
Running the 12ga to the Fuel Pump takes a little time but if you already have done it then it's there. Install that wiring tuck it up mount the Relay near the factory Fuse Box so the wire from the PCM can reach it, have to take it apart to find that wire on PCM RED 9. Clip it at whatever Connector it's in and run it to the new Relay.
Thread Starter
TECH Apprentice
Joined: Nov 2008
Posts: 322
Likes: 30
From: Arizona
A slick, so essentially utilize the fuse block to hold the relay but nothing more. Put an inline fuse on new line to the relay Pin 86. That sounds better than my idea of running a second relay. I have already run 12 Gauge wire to the pump and it's ground. Thanks!
You'll figure it out the hard way, not my problem.
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Thread Starter
TECH Apprentice
Joined: Nov 2008
Posts: 322
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From: Arizona
@Full Power thanks for the recommendation. Those look easier to work with if I rig something up outside of having a dedicated junction block. I'll have to check them out!
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Thread Starter
TECH Apprentice
Joined: Nov 2008
Posts: 322
Likes: 30
From: Arizona
I dug deeper and seems the factory Omron micro 280 relay may have been too small for my pump. The pump was drawing 11amps with the key on engine off... that's at 12.4 volts. I think the relay was rated for 10 amps. It was heating up, the cover had signs of heat stress.
I bought a micro 280 fuel pump relay for now.