2015 Massimo MSU500 No power to fuel pump

[sle2115]

2015 Massimo MSU500 was running fine, just died while idling.  I put a new fuel pump in as the original was getting noisy, but didn’t solve the problem.  I don’t see any damaged wires, and this is the first issue I’ve ever had with it.  I can hook a 12v battery to fuel pump directly and it starts fine, haven’t tried to drive it but assume it will run fine if there was power to fuel pump.  While I haven’t continuity tested the ground, I have proved the plug and there is no 12v on the appropriate wire.  As I said, plug off, alligator clip jumpers to appropriate fuel pump pins and it runs fine.  Fuse is good but looks like relay is only replaceable via replacing the whole firewall mounted unit.  Any good way to test that relay?

[Joe Breaux]

if pump runs with direct 12v  and if you have no power at plug, its either a fuse or bad wire.. fuse box is on wall under hood 

[sle2115]

Well, it wasn’t either of those, after tracing wires, cleaning every connector and adding dielectric grease, no bad wires and fuse was the first thing I checked/changed.  It was the relay, $45 on eBay and it’s now running again, with a much quieter fuel pump to boot!

[McNutt]

Which relay did you replace? I'm getting erratic voltage to fuel pump. Turn key hits 12v then drops to 5v

[Joe Breaux]

On 6/19/2023 at 1:49 PM, sle2115 said:

Well, it wasn’t either of those, after tracing wires, cleaning every connector and adding dielectric grease, no bad wires and fuse was the first thing I checked/changed.  It was the relay, $45 on eBay and it’s now running again, with a much quieter fuel pump to boot!

good job... looks like you didnt need help after all 

[Weber]

On 7/5/2023 at 8:17 AM, Joe Breaux said:

good job... looks like you didnt need help after all 

Help!  Where the heck is the fuel pump relay switch or is it in the wiring harness and you just replace that.  I called Massimo and the guy said there that it was not in the fuse/relay box.  Thanks for any help or pictures....Mark