I have replaced the batteries on my speedster and noticed there wasn't a jumper between the negative terminals as is indicated on the electrical diagram for the boat. My question is should I continue to run like this or install a jumper. I'm not sure if it came this way or someone just removed it. The boat runs fine without it.
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1996 Speedster battery replacement
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That's a great question. My 1995 Speedster is missing the jumper as well, and doesn't have any electrical gremlins that seem to be related to grounding. (plenty of other ones though! 
)
If I recall correctly, the negative terminal for one battery goes to the MPEM, and the other down under the port engine, so I could see the jumper being important, but not required to ensure the MPEM always has a consistent path to the ground on the battery, and not one that is back-fed through the starter ground on the engines, which in my best guess, establishes the ground plane of the boat.
Electrically, I can't think of any reason that the jumper would be required, but now that you've asked this question, I really want to fab one up and connect the ground on my two batteries.
So, maybe asking dcap's question in a different way, was there supposed to be a jumper between the negative battery terminals, and if not, is there any downside to installing a jumper between them?
)If I recall correctly, the negative terminal for one battery goes to the MPEM, and the other down under the port engine, so I could see the jumper being important, but not required to ensure the MPEM always has a consistent path to the ground on the battery, and not one that is back-fed through the starter ground on the engines, which in my best guess, establishes the ground plane of the boat.
Electrically, I can't think of any reason that the jumper would be required, but now that you've asked this question, I really want to fab one up and connect the ground on my two batteries.
So, maybe asking dcap's question in a different way, was there supposed to be a jumper between the negative battery terminals, and if not, is there any downside to installing a jumper between them?
USAF_Pride
Member
The reason to tie the grounds together is to ensure the batteries are at the same potential. Not to get to technical, but voltage isn't measured to "ground", it is measured to a "reference". In theory, if the batteries are not bonded together, you could have 2 different reference points. When that happens, you can get current (and voltage) flowing between the two different references (voltage in the ground system).
Tie them together to eliminate any stray voltage running through the system.
Tie them together to eliminate any stray voltage running through the system.
OK, great answers. Thanks for taking the time to reply. I've got one more if you've got the time. Recently I tried to start the motors and found the batteries not able to start them. Long story short, when I disconnected the batteries I heard a relay turn off. When I installed the new batteries the relay energized and the bilge pump came on. The bilge relay energizes any time the batteries are connected even when the float and manual switches for it are disconnected. I read a previous thread on the same problem which recommended replacing the mpem as the fix. Instead of spending that kind of money I thought I would just rewire it by interrupting the feed to the pump (always on) and routing it through the float & manual switches (in parallel) so that instead of the relay control current flowing through the switches it would be the pump current. My question is, do you see any problem with the switches being able to handle the pump current? I'm not sure what the pump current is but it is fused at 3 amps.
USAF_Pride
Member
First off, you can't buy an MPEM anymore as they no longer make them (and if you can find a used one, prepare to pay big $$$$). That being said, I don't have a wiring diagram for your boat, but you need to look at the wiring as I am unsure it runs through your MPEM.
Verify the wiring and make sure no one rewired something incorrectly. The manual switch and automatic should be in parallel and the pump shouldn't have owner with the switches disconnected
Verify the wiring and make sure no one rewired something incorrectly. The manual switch and automatic should be in parallel and the pump shouldn't have owner with the switches disconnected
Waterluvr
New Member
Sounds like your reed switch in the DESS post is not closing and leaving the MPEM powered up, you're likely experiencing a constant draw on your batteries when the boat is sitting static on the trailer right?
Testing procedures for the post and wiring are in the manual, and in several recent threads on this site if you Google search.
Looking at the wiring diagram for the '96 (I have a '95 so it is totally different) but there appears to be a relay tied to the automatic portion of the bilge pump circuit, so is it possible that either the sensor that drives this relay, or a short is causing this relay to stay engaged is causing the problem? If I am reading this diagram right, it looks like the blower, bilge pump, aux and lighting are all powered independent of the MPEM so they should "work" without the key or DESS on, correct?
Just wondering if that was the relay that dcap was hearing, and why the bilge pump came on when new batteries went in. Figuring that near dead batteries might have enough juice to hold a relay closed, but not enough to power the pump circuit.
Not questioning your expertise on this because I've already fixed like 2/3 of my electrical problems based on advise you've given, but just more trying to understand how all of these systems interact.
Waterluvr
New Member
That auto bilge runs out of the front power distribution box and it works in conjunction with the water level sensor and cycles intermittently so as not to constantly scavenge the batteries of power. If the sensor is coated with slime or manky bilge trash it will complete the circuit every time the board checks it for continuity in the circuit and turn on the pump (which you will hear running or can test for power in the supply harness if the pump is dead).
~It is fused up front so you can isolate that when chasing a draw.
~It is fused up front so you can isolate that when chasing a draw.
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