Excessive power draw or normal?

[Scottmillhouse]

Just finished wiring on my Roadster with the FFR Ron Francis harness. Everything works BUT when the ignition is on I get an immediate 1/2 volt voltage drop (checking at the starter connection). I don't get that with the other circuits. Here is where I am confused. The Brown wire provides ignition switch controlled power to the gages. With everything off it shows continuity with ground. When I disconnect the instrument harness from the main wiring it shows an open circuit as I would expect on the instrument harness that I wired in. The main harness shows continuity with ground with nothing connected on the brown wire. I normally would expect it to be an open circuit. The only thing I can think of is that there must be a relay energized that is drawing the current and showing continuity.

Thoughts?

Probably nothing to do with it but the starter just spins. Since it is used and been sitting probably 10 years, I assume the Bendix is shot unless it is possible to have one without enough reach to engage into the flywheel. Standard 1993 Mustang 302 engine with a TKO transmission.

[edwardb]

There are only three actual relays in the stock RF harness: (1) Horn, (2) Cooling fan, (3) Fuel pump. Assuming everything is correct, the only one that would energize when the key is first turned on is the fuel pump relay. That's if the inertia switch is installed and closed. Doubt the relay itself would cause a voltage drop. Probably would if actually running the fuel pump, but doesn't sound like you're that far along and don't even know if using a fuel pump. Hazard and turn signal flashers are also a kind of relay. If you have those hooked up to lights, might cause a slight voltage drop. Do you have EFI or ignition coil or choke wired? Any of those could cause some draw and a slight drop. What about your battery itself? What condition? That's probably the first thing I would check. Assuming you have good ground(s), IMO not much to be learned by the continuity checks your describing.

[Scottmillhouse]

There are only three actual relays in the stock RF harness: (1) Horn, (2) Cooling fan, (3) Fuel pump. Assuming everything is correct, the only one that would energize when the key is first turned on is the fuel pump relay. That's if the inertia switch is installed and closed. Doubt the relay itself would cause a voltage drop. Probably would if actually running the fuel pump, but doesn't sound like you're that far along and don't even know if using a fuel pump. Hazard and turn signal flashers are also a kind of relay. If you have those hooked up to lights, might cause a slight voltage drop. Do you have EFI or ignition coil or choke wired? Any of those could cause some draw and a slight drop. What about your battery itself? What condition? .

Ok battery Odyssey fully charged at 12.8 volts, All fuses and circuits connected shows 12.8 at starter, drop occurs when ignition is switched to on. Already disconnected MSD ignition and choke with no effect. Full pump works fine. On switch that opens circuit to roll over switch so there is no power to fuel pump relay. Going to try disconnecting alternator to see if any affect. (Done, no affect, does sound like something is energizing in fuse box when turning ignition switch) Then remove starter for checkout. (Removed, Starter is correct so Bendix must be bad)

First start when debugged.

[Papa]

Which wires are you running to the ignition switch? The alternator (brown) wire should not be connected to the switch or the alternator.

[Scottmillhouse]

Which wires are you running to the ignition switch? The alternator (brown) wire should not be connected to the switch or the alternator.

I believe you are correct with the gen 6 one wire alternators but I have a gen 3 which I believe uses that brown wire from the ignition to energize the voltage regulator. The brown ones I’m talking about are for the instrument harness that connects to the main harness. Regardless the alternator is not the problem because I tested with all the alternator wires disconnected and still have the voltage drop.

[frankeeski]

Let's go over a few basics. When you turn the ignition switch to the ACC or RUN position power is sent to the gauges (electronic/electric gauges) and that power has a path back to ground. It will show continuity to ground on both side when the ignition switch is off, it's reading through the circuit of the gauge. Also when the IGN switch is on RUN you'll be sending power through the ignition coil. Again, that will read continuity to ground on both sides when the switch is off. Your ignition box, same thing. 1/2 volt of draw when the switch is in the run position doesn't sound like an issue. Here's a question though, are you using a multimeter on the battery terminal to measure when you're doing this testing or are you using the voltage gauge in the dash?

[CraigS]

Reading voltage is not how a drain is measured. It should be measured w/ an amp meter that will read in milli-volts. Disconnect the battery cable and put one meter lead on the cable end. Put the other lead on the battery post. With everything turned off you want < 50 milli amps. Having a 1/2V less at the starter when the key is on sounds normal to me.

[Erik W. Treves]

Reading voltage is not how a drain is measured. It should be measured w/ an amp meter that will read in milli-volts. Disconnect the battery cable and put one meter lead on the cable end. Put the other lead on the battery post. With everything turned off you want < 50 milli amps. Having a 1/2V less at the starter when the key is on sounds normal to me.

agreed

[Boydster]

Reading voltage is not how a drain is measured. It should be measured w/ an amp meter that will read in milli-volts. Disconnect the battery cable and put one meter lead on the cable end. Put the other lead on the battery post. With everything turned off you want < 50 milli amps. Having a 1/2V less at the starter when the key is on sounds normal to me.

Agreed x2. Dont turn the key on unless your meter is made for the power-on load.

[Scottmillhouse]

I guess the representation of voltage drop was normal and not excessive. Even though it checked out ok the problem was actually a defective and wrong starter. It would not spin up as well with reduced voltage as connected directly and it did not have the reach to engage the flywheel. New and correct starter and had first start. Lots of bugs had to be fixed but now it is running fine. Now a few more things and the go-cart goes around the block then on to interior and body installation.

[Theshandman]

This thread seems like a good one to ask this question. What would you expect the current draw to be at the batt when the ignition is turned on, but not to start? I'm at the point where I'm checking the wiring for possible shorts between +/-.
To set up my test environment: BPE 347 FI installed, connected at both the dedicated batt pos and neg, and the pink "always on" connected at the ignition switch. I have the RF harness connected to all dash elements including the ignition switch. I haven't connected the fuel pump at the tank to avoid possible damage to the unloaded pump (no fuel pending first start). No lights of any kind are connected much less installed although those switches are wired. No obvious shorts in the dangling lighting wires. Lights and wiper switches both off.
With ignition off, current draw at the batt is 0.013A; no system shorts. Neg connectors firm at the batt, Pos connector is free, and I put in a 1A fuse on a pigtail to the plus cable as a sacrificial test circuit fuse then connected the other end to the plus batt term. No blow at this point. But, the 1A fuse blew almost immediately when the ignition was switched on. I saw a very brief excursion of a few gauges (too fast to note which ones exactly) and heard what sounded like a relay (fuel pump?) before the fuse blew.
So- would you expect more than 1A draw at the batt with all correct wiring with ignition on? At this point, I really don't want to use higher rated fuses to keep "testing" my wiring.

[Mastertech5]

This thread seems like a good one to ask this question. What would you expect the current draw to be at the batt when the ignition is turned on, but not to start? I'm at the point where I'm checking the wiring for possible shorts between +/-.
To set up my test environment: BPE 347 FI installed, connected at both the dedicated batt pos and neg, and the pink "always on" connected at the ignition switch. I have the RF harness connected to all dash elements including the ignition switch. I haven't connected the fuel pump at the tank to avoid possible damage to the unloaded pump (no fuel pending first start). No lights of any kind are connected much less installed although those switches are wired. No obvious shorts in the dangling lighting wires. Lights and wiper switches both off.
With ignition off, current draw at the batt is 0.013A; no system shorts. Neg connectors firm at the batt, Pos connector is free, and I put in a 1A fuse on a pigtail to the plus cable as a sacrificial test circuit fuse then connected the other end to the plus batt term. No blow at this point. But, the 1A fuse blew almost immediately when the ignition was switched on. I saw a very brief excursion of a few gauges (too fast to note which ones exactly) and heard what sounded like a relay (fuel pump?) before the fuse blew.
So- would you expect more than 1A draw at the batt with all correct wiring with ignition on? At this point, I really don't want to use higher rated fuses to keep "testing" my wiring.

A 1 amp fuse will blow with the ignition switch on. Anything you have connected is going to draw more than 1amp. You can check the amperage draw with a volt/ohm meter connected the same as your 1amp fuse. Configure your meter for reading amps on the highest risk setting of auto if it has it, usually 10 to 15 amps and turn your key on. Auto function will tell you what amp draw you have manual dial selection may require you to move the decimal point to get the proper amp reading. Your ignition off reading of 13 milliamps is normal. If you have a dead short any automotive sized fuse will blow. The fuse in the fuse block for a shorted circuit should blow, which are all more than 1amp.

[Windsor]

For reference, a 15w incandescent bulb is gonna flow more than 1 amp.