85 ford Ltd country squire 302 I’m finalizing an upgrade from CFI to the MAF efi from an 89 mustang. My problem: my tach jumps when wipers are turned on. Have an auto meter 7000 gauge. Before the wiring upgrade, no problems. Now the wiper is sending a signal somehow to the tach. Nothing under dash was rewired. Just replaced ignition switch. Only wipers does it. Nothing else causes it. When I unplug run power to dizzy and coil, problem goes away. My eyes are crossed. thanks
That's a new one on me. It's not any easier that the tach and EFI are upgrades. Start with unplugging just the tach. Does it start and run?
my man I owe you drink! Took that circuit straight to the battery and problem gone. So I just need to find a different ignition circuit to run that on or more the wipers off of that one.
At this moment it will not run, fuel pump check valve faulty. So I’m not building up pressure and not filling up the rail. The tach was on the CFI and worked like a champ for nearly a year. It’s some really weird interference/feedback along the circuits piggy backing on the ground/tach lines. I believe it must have something to due with the different harnesses now. But it could be that my wiper motor is on the fritz and about to die, Tis original. But with the advice from wagonrodder, the problem can now be eliminated today or least bypassed. It’s only affecting the tach. Blower, radio, lights, etc are not going crazy, nor screwing with the tach
I read your other post; the fuse box has both BAT and IGN terminals to power your tach from directly. You should use a 10 amp inline fuse holder on the power wire, and of course, use one of the IGN terminals.
At the moment, power off the battery, through a control relay, doesn’t mess with the gauge……..90% of the time. I sat in the car, key on, wipers on intermittent and low mostly, as that speed is causing the jump. Have a battery tender to maintain charge. But I’d added and removed load for over an hour. Increasing wiper speed to high a few times. Only one blip of whatever is going on, showed up only when the wiper was going to park. I could not get it to show up again. I tried adding a ground to the wiper motor directly to battery, no change. I tried moving the ign power to another power wire, the gremlin is still there. Doesn’t matter what wire I use, the closer to the fuse box, the problem is there, move away and it’s gone, mostly. I’m not popping fuses, blowing breakers, nothing is getting hot, or smoking. attached is my gauge cluster. The tach is just a signal wire from the coil. The ballast resistor is still installed.
I see what you did there. I assumed you had a standalone tach, like the Autometer one I have, but apparently you have installed a full digital cluster. If I had to guess the problem, now that I know this, your power wire is picking up spurious electrical noise from the wiper motor at or near the fuse panel. You can assemble a temporary relay power circuit, powered from the fuse box IGN terminal, and the controlled power circuit, to feed the cluster, comes from the battery. Wire that in, then retest. I found that those smaller 5-terminal relays you find in Ford fuse boxes from the early Nineties up work really well. Oh, and verify that your body-to-engine, engine-to-frame and frame-to-battery ground straps and cables are clean and in good condition, 'just because'. It popped into my head that your cluster's ground path may be what's compromised, and spurious noise can't make it through the filter circuitry to ground. Remember, these are electricals, and they can have a host of problems in an older car.
You reminded me that I DID change wiring under the dash. Very small. The ground to the cluster. I originally had it on the battery, but relocated it to a ground bud bar under the dash. Just hooked it directly to battery. There’s still interference, but significantly less. Tomorrow I’ll relocate both ign and constant power for the cluster side note: I went with this gauge last year after the speedo cable failed and the original gauge failed too. I wanted to have a more low key looking cluster with actual needles, but nothing would fit properly. I wanted actual readouts from the engine vrs idiot lights. This setup has been wonderful. Setting idles on the old cfi was made easier with this. Plus I can monitor temp, pressure, and battery. This thing has 4 displays, and one that you can change the color on. I absolutely love it
UPDATE: Two problems discovered. One: the tach was hooked up prior to ballast. Was hooked up after ballast on old harness. That helped. Two: the cowl is not grounded very well. The old harness must of had a cable connected. And when I grounded the wiper motor the other day, I did t have it right. Today I have it grounded properly to the battery…….gremlin gone!!!!
Remember, the cowl ground path goes to the back of both cylinder heads--one 14-ga cable driver side, one braided strap passenger side. Those give the cowl it's ground path. There's also a ground wire from the engine harness to the rear of the lower intake on the port FI (perhaps even two, I'd have to look on Roger's harness and intake), which some have forgotten to install when making repairs on the engine or fuel injection.
