"True" ignition source?

Hi all, I'm installing a second battery with a Stinger SR200 relay. I'm having some trouble finding the true ignition source (stays at 12v even when cranking). I've probed the wires from the dash to the engine in off-on-cranking, and have failed to find a wire that doesn't drop its voltage. My engine is a 01 Merc 4.3EFI. Can anybody offer any advice?
Thanks,
Mike

Mike:

I wish I could help, but I'm also trying to wire a relay and having problems. How did you wire the relay in regards to both batteries?

Thanks,

Tim

Mike:

When you say "doesn't drop its voltage", how much drop are you talking about?

I would fully expect the battery voltage to drop to 11 volts or lower while cranking the starter.

Rod

fuel pump gauge wire or fuel pump power wire will work.get a test light and check connections with switch off then check with switch on. anything that works with the switch on and not with it off will work.dont worry about the volts while cranking, you want it to charge while the engine is running and be isolated when it is off.

Tim: go to www.stingerelectronics.com and you can download a pdf of the wiring diagram. Even if your relay is a different brand, I can't imagine it would be too different.

Rod: A drop to 11 volts would be acceptable, however, I can't manage to find a wire that doesn't measure what I would assume to be a cutoff drop. One thought I had that I haven't tried, it disconnecting the spark plug wire that connects the coil to the distributor, so I can get a longer cranking time, and thus, a longer probe time on the wire. As it is, I have to just hit the starter briefly and watch the voltage on my meter.

Thanks dodge, I didn't know if it was imperative that both batteries contribute to the starting process. I figured that one of the points of the dual battery system was that if the main one died, the alternate one could provide starting power through the relay. As it is, the second battery is just for the stereo, so it doesn’t really matter that much.

Hey Mike,
Are you and have you considered using a perko dual battery switch? It's a pretty handy switch to have especially since you can have the ability to turn everything off when not in use. Feel free to give me a call and I'll ask the service dept any questions for ya, it's been a while since we've talked!

if you want to use one as a backup for starting then i would get a switch but if you are using it as a stereo battery the relay will work good. i have mine was like this 2 batteries for radio and amps with relay to one starting battery so i can charge the 2 radio batteries while riding and not drain the starting batt with key off while just playing the radio then i have a switch to the other battery just in case i kill the other ones. i will try to post a pic

here ya go the realy and switch are on the right side

just get a "combiner" from West Marine.com. It is about $70 for the 50 amp one and it works great.. It "combines" the 2 batteries when charging but keeps them separate for use. On mine I have one starting only battery and one for stereo/amp/lights/inverter/ballast pumps. The combiner will keep the starting battery separate so it will always be ready.. It's automatic and no switch is necessary.. Ultimate setup is 2 boat batteries with a Perko Switch (1 on/ 2 on/ both on/ both off) so you always have a backup battery in case you ran your stereo battery dry and the other failed.. then you could switch to the backup for starting.. but that is overkill IMO. 2 batteries, one combiner good to go.. Unless you are like the guy above and need 4 batteries.. 2 for just his stereo stuff.. then.. well it's beyond me..

Well, I bought the relay based on posts from here and frankly, I'm not going to spend any more money on the project. What I do seem to understand now though is that a relay is not a good solution for a backup battery. This is fine since it's for the stereo. Thanks for your help everyone.
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