I have an 86 mercury 35hp does the engine control have an electrical accessory hookup? to power gauges lights etc?

Your vehicle has electronic throttle control , do you know what that is ? Any lights lit on the instrument cluster , wrench symbol , check engine light , reduce engine power ?
Ford ETC System

A dead short to ground on that circuit . Do you know anything about automotive electric diagnostic's ? Video's on youtube for finding shorts . Which fuse ? # what fuse box ? Does it supply battery voltage to anything else on the vehicle. Looking at a wiring diagram I see fuse F2.6 a 15amp fuse located in the central junction box. And it powers other circuits . I also see two other fuse's that power the insturment cluster . F2.23 - 15 amp and F2.14 a 10 amp . Do you know what a wiring diagram is ? Free diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. year , make , model and engine . Under system click on body & accessories then under subsystem click on instrumentation . Click the search button then the blue link's .

the serial number begins 2487558 and continues past 2491265 and as the beginning serial number denotes the year , your engine is 1969 model
it shows as a 2 stroke with auto oil injection
check the heads
if the plugs are in the flat of the head and there are no rocker covers it is 2 stroke
talk with a mercury /mariner service center

If it is the same as a Nissan Sentra, and Nissans were pretty standard, those two would be the accessory relay on the far left and the ignition relay next to it. The other two relays are the fuel pump relay and the ECCS relay (for the engine computer operation).

Does the engine still start and run? The ignition relay doesn't affect engine running. It's primary purpose is to power up that portion of the fuse block that the accessory relay does not cover, like the dash gauges and warning lights and turn signals, a few other too, I think..

If you are trying to make it work simultaneously with stock horns, I suggest you wire it in through a relay. Without a relay you will be placing too much of a load on the horn circuit.
A relay is typically used to control a component that draws high amperage. The relay allows full power to the component without needing a switch that can carry the amps. The switch only controls the relay. The relay then provides a direct connection to the battery. It should be noted that either the power(86) or ground(85) in the relay control circuit can be switched. In the case of a horn, the horn button would be used to switch the ground lead(85) and power(86) would be provided directly from the fuse box.
This is a typical wiring diagram for a standard relay installed for headlights, horn, fuel pump, electric fan, etc. If the relay has a 5th terminal, it is not used.

Do you know anything about electronic's ? Automotive electronic's take more of a beating , hitting bump's , pot holes ,curbs etc. Enough to jar even the best built electronic componets . Chrysler products have had solder joint's crack , causing intermittent connection problems , could be loose fitting electrical connection's etc.... There is a microprocessor with logic programmed into it , inside the instrument cluster , the gauges ,warning light's are all controlled by modules . The gauges get their info from the PCM/ECM - engine computer over what is called a serial data network , are you familiar with these . The PCI data bus is what it is called . NO Communication issues on 2003 Dodge 1500 trucks is best fixed using...

Probably the best thing to do would be to have the whole vehicle scanned for DTC'S - diagnostic trouble code's . Not at a part's store , they can not read codes in the instrument cluster , BCM - body control module etc.

You could probably check power an ground connections for the IPC , Looking at a wiring diagram so you know which wire's to check . Free wiring diagrams here http://www.bbbind.com/free_tsb.html Enter vehicle info. year,make ,model an engine size . Under system click on body & accessories ,then under subsystem click instrumentation .Click search button ,then the blue link. To find ground location's on the vehicle you real need some kind of factory service info. or repair manual .

check the coil maybe it needs replaced

Let's see what we have here,
Battery is hot
fuel gauge and light hot
Ignition hot
starter hot
What we don't have
no accessory lights and the starter won't turn the engine over.

I'm sorry but I don't have a schematic for your bike to refer to but usually Harley puts instruments, lights, ignition, and accessories on separate fuses or breakers. Sounds like you've blown the accessories fuse as I think this one controls power to the starter relay. I think your fuses are behind the electrical panel on the left side of the bike.

timer on what ? make, model and age of unit might be useful in forming a coherent response.

Hi,sound like a bad (tps , trotle position sensor, Good Luck